0001193125-26-263731 | S-4/A | XBRL Viewer | Cyclerion Therapeutics INC

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

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Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Accounting Policies [Abstract]

2. Summary of Significant Accounting Policies

The accounting policies of the Company are set forth in Note 2.

Summary of Significant Accounting Policies

to the consolidated financial statements contained in the Company’s Annual Report on Form

10-K

for the fiscal year ended December 31, 2025.

New Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Except as discussed elsewhere in the notes to the interim condensed consolidated financial statements, the Company did not adopt any new accounting pronouncements during the three months ended March 31, 2026 that had a material effect on its condensed consolidated financial statements.

No other accounting standards known by the Company to be applicable to it that have been issued by the FASB or other standard-setting bodies and that do not require adoption until a future date are expected to have a material impact on the Company’s condensed consolidated financial statements upon adoption.

2. Summary of Significant Accounting Policies

Segment Information

The Company operates and manages its business as a single segment for the purposes of assessing performance and making operating decisions. The Company’s president and chief executive officer, who is the chief operating decision maker (“CODM”), reviews the Company’s financial information on a consolidated basis for purposes of evaluating financial performance and allocating resources. When evaluating the Company’s financial performance, the CODM regularly reviews net loss,

non-operating

expenses and operating expenses excluding

non-cash

stock based compensation expense.

Variable Interest Entities

The Company reviews each legal entity in which it has a financial interest to determine whether or not the entity is a variable interest entity or VIE. If the entity is a VIE, the Company assesses whether or not it is the primary beneficiary of that VIE based on a number of factors, including (i) which party has the power to direct the activities that most significantly affect the VIE’s economic performance, (ii) the parties’ contractual rights and responsibilities pursuant to any contractual agreements and (iii) which party has the obligation to absorb losses or the right to receive benefits from the VIE. If the Company determines that it is the primary beneficiary of a VIE, it consolidates the financial statements of the VIE into its consolidated financial statements at the time that determination is made. On a quarterly basis, the Company evaluates whether it continues to be the primary beneficiary of any consolidated VIEs. If the Company determines that it is no longer the primary beneficiary of a consolidated VIE, or no longer has a variable interest in the VIE, the Company deconsolidates the VIE in the period that the determination is made.

Investment

The Company accounts for investments in equity securities without a readily determinable fair value at cost, minus impairment. If the Company identifies observable price changes in orderly transactions for an identical or a similar investment of the same issuer, the Company will measure the equity security at fair value as of the date that the observable transaction occurred in accordance with ASC Topic 321, Investments-Equity Securities.

Use of Estimates

The preparation of consolidated financial statements in accordance with U.S. generally accepted

accounting

principles (“GAAP”) requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the

consolidated financial statements, and the amounts of expenses during the reported periods. On an ongoing basis, the Company’s management evaluates its estimates, judgments and methodologies. Significant estimates and assumptions in the consolidated financial statements include those related to revenue, fair value determination of other investment, income taxes, including the valuation allowance for deferred tax assets, research and development expenses, contingencies, share-based compensation and going concern. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ materially from these estimates under different assumptions or conditions. Changes in estimates are reflected in reported results in the period

which they become known.

Cash and Cash Equivalents

The Company considers all highly liquid investment instruments with a remaining maturity when purchased of three months or less to be cash equivalents. Investments qualifying as cash equivalents may consist of money market funds and overnight repurchase agreements. The carrying amount of cash equivalents approximates fair value.

Fair Value of Investment Instruments

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•

Level 1 — Quoted prices in active markets for identical assets or liabilities.

•

Level 2 — Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•

Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

Foreign Currency Translation Adjustment

The functional currency of the Company’s former foreign subsidiary is its local currency, the Swiss franc. The assets and liabilities of the Company’s former foreign subsidiary are translated into U.S. dollars at exchange rates in effect at the balance sheet date. Income and expense items are translated at the average exchange rates prevailing during the period. The cumulative translation effect for the Company’s former foreign subsidiary was included as a foreign currency translation adjustment in the consolidated statements of stockholders’ equity and as a component of comprehensive loss in the consolidated statements of operations and comprehensive loss.

The Company’s intercompany accounts are typically denominated in the functional currency of the foreign subsidiary. Gains and losses resulting from the

re-measurement

of intercompany balances are recorded in the consolidated statements of operations.

Accounts Receivable

The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for receivables when collection becomes doubtful. Provisions are made based upon a specific review of all

significant outstanding invoices. The Company believes that credit risks associated with these agreements are not significant. To date, the Company has not had

significant

write-offs of bad debt and the Company did not have an allowance for doubtful accounts as of December 31, 2025 or 2024.

Revenue

Upon executing a revenue generating arrangement, the Company assesses whether it is probable the Company will collect consideration in exchange for the good or service it transfers to the customer. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC Topic 606,

Revenue from Contracts with Customers

(“ASC 606”), it performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies the performance obligations. The Company must develop assumptions that require significant judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The assumptions that are used to determine the stand-alone selling price may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success. The Company derives revenue from (1) license agreement, (2) purchase agreement and (3) option to license agreement which are fully described in Note 11,

License and Option Agreement

Research and Development Costs

The Company expenses research and development costs to operations as incurred. The Company defers and capitalizes nonrefundable advance payments made by the Company for research and development activities until the related goods are received or the related services are performed. The Company estimates the period over which such services will be performed and the level of effort to be expended in each period. If actual timing of performance or the level of effort varies from the estimate, the Company will adjust the amounts recorded accordingly. The Company has not experienced any material differences between accrued or prepaid costs and actual costs since inception.

Research and development expenses are comprised of costs incurred in performing research and development activities, which may include salary, benefits and other employee-related expenses; share-based compensation expense; laboratory supplies and other direct expenses; facilities expenses; overhead expenses; third-party contractual costs relating to nonclinical studies and clinical trial activities and related contract manufacturing expenses, development of manufacturing processes and regulatory registration of third-party manufacturing facilities; and other outside expenses.

General and Administrative Expenses

The Company expenses general and administrative costs to operations as incurred. General and administrative expense consists of compensation, share-based compensation, benefits and other employee-related expenses for personnel and outside consultants providing the Company’s administrative, finance, legal, information technology, business development and human resource functions. Other costs include the legal costs of pursuing patent protection of the Company’s intellectual property, general and administrative related facility costs, insurance costs and professional fees for accounting and legal services.

Income taxes

The Company is primarily subject to U.S. Federal and Massachusetts state income taxes. For federal and state income taxes, deferred tax assets and liabilities are recognized based upon temporary differences between the financial statement and the tax basis of assets and liabilities. Deferred income taxes are based upon prescribed rates and enacted laws applicable to periods in which differences are expected to reverse. A valuation allowance

is recorded when it is more likely than not that some portion or all of the deferred tax assets will not be realized. Accordingly, the Company provides a valuation allowance, if necessary, to reduce deferred tax assets to amounts that are realizable.

The tax positions taken or expected to be taken in the course of preparing the Company tax returns are required to be evaluated to determine whether the tax positions are

“more-likely-than-not”

of being sustained by the applicable tax authority. Tax positions not deemed to meet a

more-likely-than-not

threshold would be recorded as a tax expense in the current year. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. It does not consider the likelihood of whether or not the IRS will review the position. Cyclerion evaluates uncertain tax positions on a quarterly basis and adjusts the level of the liability to reflect any subsequent changes in the relevant facts surrounding the uncertain positions. Any changes to these estimates, based on the actual results obtained and/or a change in assumptions, could affect Cyclerion’s income tax provision in future periods. There were no uncertain tax positions that require accrual or disclosure in the consolidated financial statements as of December 31, 2025, and 2024. The Company’s policy is to recognize interest and penalties related to income tax, if any, in income tax expense. As of December 31, 2025 and 2024, the Company has no accruals for interest or penalties related to income tax matters.

Patent Costs

Patent fees and patent related costs in connection with filing and prosecuting patent applications are expensed as incurred and are classified as general and administrative expenses in the accompanying consolidated financial statements. The Company incurred and recorded as operating expense legal and other fees related to patents of approximately $0.3 million and $0.6 million for the years ended December 31, 2025 and 2024, respectively.

Interest and Other Income, Net

For the year ended December 31, 2025 and 2024, interest and other income, net consisted of a $0.1 million and $0.2 million of interest income related to interest generated from the Company’s cash and cash equivalents balances, respectively.

Subsequent Events

The Company considers events or transactions that have occurred after the balance sheet date of December 31, 2025, but prior to the filing of the financial statements with the Securities and Exchange Commission, to provide additional evidence relative to certain estimates or to identify matters that require additional recognition or disclosure. Subsequent events have been evaluated through the filing of the financial statements accompanying this Annual Report on Form

10-K.

See Note 12,

Subsequent Events

Recently Issued Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Except as discussed elsewhere in the notes to the consolidated financial statements, the Company did not adopt any new accounting pronouncements during the years ended December 31, 2025 and 2024, that had a material effect on its consolidated financial statements.

In August 2025, the FASB issued ASU

No. 2025-05,

Financial Instruments—Credit Losses (Topic 326), which requires incremental disclosures on estimating expected credit losses. The Company will adopt this guidance beginning with its annual report for fiscal 2027. The Company is currently evaluating the potential effect that the updated standard will have on its financial statement disclosures.

Recently Adopted Accounting Pronouncements

In November 2023, the FASB issued ASU

No. 2023-07,

Improvements to Reportable Segment Disclosures (Topic 280), which requires incremental disclosures on reportable segments, primarily through enhanced disclosures on significant segment expenses. The Company adopted this guidance beginning with its annual report for fiscal 2025 and interim periods thereafter on a retrospective basis. The adoption did not have a material effect on the consolidated financial statements.

In December 2023, the FASB issued ASU

No. 2023-09,

Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which focuses on the rate reconciliation and income taxes paid. ASU

No. 2023-09

requires a public business entity (PBE) to disclose, on an annual basis, a tabular rate reconciliation using both percentages and currency amounts, broken out into specified categories with certain reconciling items further broken out by nature and jurisdiction to the extent those items exceed a specified threshold. In addition, all entities are required to disclose income taxes paid, net of refunds received disaggregated by federal, state/local, and foreign and by jurisdiction if the amount is at least 5% of total income tax payments, net of refunds received. For PBEs, the new standard is effective for annual periods beginning after December 15, 2024, with early adoption permitted. For entities other than PBEs, the requirements will be effective for annual periods beginning after December 15, 2025. An entity may apply the amendments in this ASU prospectively by providing the revised disclosures for the period ending December 31, 2025 and continuing to provide the

pre-ASU

disclosures for the prior periods, or may apply the amendments retrospectively by providing the revised disclosures for all period presented. As of December 31, 2025, the Company adopted this new ASU and it only impacts the Company’s income tax disclosures with no impact to its operations, cash flows, or financial condition.

Loss per share

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Earnings Per Share [Abstract]

Loss per share

8. Loss per share

Basic and diluted net loss per common share is computed by dividing net loss by the weighted average number of common shares outstanding during the period as follows:


	Three Months Ended March 31,
	2026			2025
Numerator:
Net loss (in thousands)	$	(3,177	)	$	(1,429	)
Denominator:
Weighted average shares used in calculating net loss per share — basic and diluted (in thousands)		4,205			2,556

Net loss per share — basic and diluted	$	(0.76	)	$	(0.56	)

The Company excludes shares of common stock related to Preferred Stock, stock options and RSAs from the calculation of diluted net loss per share since the inclusion of such shares would be anti-dilutive. The following table sets forth potential shares that were considered anti-dilutive for the three months ended March 31, 2026 and 2025:


	Three Months Ended March 31,
	2026		2025
Preferred Stock		351,037		351,037
Stock Options		280,407		329,458
RSAs		89,054		149,150

		720,498		829,645

8. Loss per share

Basic and diluted net loss per common share is computed by dividing net loss by the weighted average number of common shares outstanding during the period as follows:


	Year Ended December 31,
	2025			2024
Numerator:
Net loss (in thousands)	$	(3,528	)	$	(3,057	)
Denominator:
Weighted average shares used in calculating net loss per share — basic and diluted (in thousands)		3,181			2,518

Net loss per share — basic and diluted	$	(1.11	)	$	(1.21	)

The Company excludes potential shares of common stock related to Preferred Stock, stock options and RSAs from the calculation of diluted net loss per share since the inclusion of such shares would be anti-dilutive. The following table sets forth potential shares that were considered anti-dilutive for the years ended December 31, 2025 and 2024:


	Year Ended December 31,
	2025		2024
Preferred Stock		351,037		351,037
Stock Options		297,762		335,448
RSAs		104,078		164,174

		752,877		850,659

Nature of Business (Details)									1 Months Ended	3 Months Ended		12 Months Ended
Nature of Business (Details)	Apr. 01, 2026 USD ($) $ / shares	Jan. 06, 2026 USD ($)	Jan. 03, 2026 USD ($)	Dec. 01, 2025 USD ($)	May 07, 2025 USD ($)	Mar. 21, 2025 USD ($) $ / shares shares	Dec. 13, 2024 USD ($)	Jul. 28, 2023 USD ($)	Aug. 31, 2024 USD ($)	Mar. 31, 2026 USD ($) $ / shares shares	Mar. 31, 2025 USD ($)	Dec. 31, 2025 USD ($) $ / shares shares	Dec. 31, 2024 USD ($) $ / shares	Dec. 31, 2023 USD ($)	Dec. 31, 2021 USD ($)	Feb. 04, 2025 USD ($)	Mar. 31, 2023 USD ($) $ / shares shares
Nature of Business
Option fee									$ 150,000
Subsequent fees									$ 80,000
Cash consideration transferrred								$ 8,000,000
Operating expenses								$ 2,400,000		$ 3,209,000	$ 1,538,000	$ 7,047,000	$ 5,628,000
Equity investment in cash																	$ 5,000,000
Preferred stock, par value (in dollars per share) \| $ / shares										$ 0		$ 0	$ 0
Proceeds from stock purchase agreement										$ 0	1,375,000	$ 1,375,000	$ 0
Maximum amount of aggregate initial offering price																$ 25,000,000
Cash commission of gross proceeds of sales of common stock, percentage					3.00%
Common stock, par value (in dollars per share) \| $ / shares										$ 0		$ 0	$ 0
Cyclerion
Nature of Business
Up front payment received							$ 1,750,000						$ 1,250,000
Remaining additional up front payment													$ 500,000
Akebia
Nature of Business
Additional milestone cash payment										$ 557,500,000		$ 557,500,000
Up front payment received															$ 3,000,000
Development milestone payment				$ 1,000,000										$ 1,000,000
Sales Agreement [Member]
Nature of Business
Proceeds from stock purchase agreement										$ 800,000		$ 2,100,000
Sale of shares \| shares										405,000		715,220
Maximum
Nature of Business
Maximum amount of aggregate initial offering price					$ 20,000,000
Maximum \| Sales Agreement [Member]
Nature of Business
Commissions paid												$ 100,000
Subsequent Event [Member]
Nature of Business
Up front payment received			$ 3,700,000
Proceeds from stock purchase agreement		$ 800,000
Series A Preferred Stock
Nature of Business
Preferred stock, shares issued \| shares																	351,037
Preferred stock, par value (in dollars per share) \| $ / shares																	$ 8.68
Common Stock
Nature of Business
Common stock shares issued \| shares																	225,000
Sale of shares \| shares										405,000		715,220
2025 Equity Private Placement
Nature of Business
Transaction costs associated with sale of transferred assets											$ 100,000
2025 Equity Private Placement \| Common Stock
Nature of Business
Common stock shares issued \| shares						499,998
Common stock share purchase price \| $ / shares						$ 2.75
Proceeds from stock purchase agreement						$ 1,375,000
Korsana
Nature of Business
Net cash on capitalization										$ 0
Korsana \| Subsequent Event [Member]
Nature of Business
Number of common shares	1.1009
Aggregate purchase price	$ 380,000,000
Korsana \| Series A Preferred Stock \| Subsequent Event [Member]
Nature of Business
Preferred stock, par value (in dollars per share) \| $ / shares	$ 0.0001
Korsana \| Series Seed Preferred Stock \| Subsequent Event [Member]
Nature of Business
Preferred stock, par value (in dollars per share) \| $ / shares	0.0001
Korsana \| Common Stock \| Subsequent Event [Member]
Nature of Business
Common stock, par value (in dollars per share) \| $ / shares	$ 0.0001
Cyclerion \| Common Stock \| Subsequent Event [Member]
Nature of Business
Percentage of outstanding shares	9.99%
Tisento Therapeutics Holdings Inc
Nature of Business
Outstanding equity securities								10.00%

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Accrued Liabilities and Other Liabilities [Abstract]
Professional fees	$ 984	$ 143	$ 220
Employee compensation	21	13	33
Other	104	38	30
Accrued expenses and other current liabilities	$ 1,109	$ 194	$ 283

Defined Contribution Plan (Details)	12 Months Ended
Defined Contribution Plan (Details)	Dec. 31, 2025 USD ($)
Defined Contribution Plan
401 (k) Savings Plan	Qualified Plan [Member]
Matching contribution (as a percent of employee's contributions)	75.00%
Maximum amount of employer matching contribution	$ 6,000
Minimum
Defined Contribution Plan
Percent of compensation eligible employees may elect to contribute	1.00%
Maximum
Defined Contribution Plan
Percent of compensation eligible employees may elect to contribute	100.00%

Share-based Compensation Plans - Schedule of Weighted Average Assumptions used in estimating the fair value of the stock options (Details)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Weighted average risk-free interest rate	3.79%	3.64%
Expected dividend yield	0.00%	0.00%
Expected option term (in years)	5 years 4 months 24 days	6 years
Expected stock price volatility	141.07%	111.97%

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Income Taxes
Deferred tax assets, valuation allowance	$ 170,000	$ 566,000
Tax credit carryforwards	10,800,000
Unrecognized tax benefits	0	0
Accrued interest or penalties	0	0
Federal
Income Taxes
Net operating loss carryforwards	$ 211,000,000	195,000,000
Income tax credit expiration description	Federal credits begin to expire in 2039 and will continue to expire through 2044. State credits begin to expire in 2034 and continue through 2039
State
Income Taxes
Net operating loss carryforwards	$ 212,000,000	$ 196,000,000
Income tax credit expiration description	begin to expire in 2039 and will continue to expire through 2045

Loss per share - Schedule of Basic and Diluted Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Numerator:
Net loss	$ (3,177)	$ (1,429)	$ (3,528)	$ (3,057)
Denominator:
Weighted average shares used in calculating net loss per share - basic	4,205	2,556	3,181	2,518
Weighted average shares used in calculating net loss per share - Diluted	4,205	2,556	3,181	2,518
Net loss per share
Net loss per share - Basic	$ (0.76)	$ (0.56)	$ (1.11)	$ (1.21)
Net loss per share - Diluted	$ (0.76)	$ (0.56)	$ (1.11)	$ (1.21)

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482662/260-10-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
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-Section 50
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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Schedule of Components of Net Income Loss Before Income Tax Expense

Share-based Compensation Plans - Summary of RSA activity (Details) - Restricted Stock Awards - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested at the beginning of the period (in shares)	104,078	164,174	164,174
Granted (in shares)	0	0	0	65,000
Vested (in shares)	(15,024)		(60,096)
Forfeited (in shares)	0		0
Unvested the end of the period (in shares)	89,054		104,078	164,174
Weighted-Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)	$ 2.57	$ 2.56	$ 2.56
Granted (in dollars per share)	0		0
Vested (in dollars per share)	2.52		2.52
Forfeited (in dollars per share)	0		0
Unvested restricted common stock at the end of the period (in dollars per share)	$ 2.59		$ 2.57	$ 2.56

Other Investment	3 Months Ended	12 Months Ended
Other Investment	Mar. 31, 2026	Dec. 31, 2025
Investments, All Other Investments [Abstract]
Other Investment	4. Other Investment The Company has determined that the Company’s investment in Tisento Parent is an equity security, whereby such investment does not give the Company a controlling financial interest or significant influence over the investee. Further, the Company assessed the accounting for its investment in Tisento Parent in accordance with ASC 810-10, Consolidation—Overall. After determining that no scope exception applies under the guidance of ASC 810-10-15-12 and ASC 810-10-15-17, the Company concluded that it has a variable interest in Tisento Parent through its investment in Tisento Parent common stock. Tisento Parent does not have sufficient equity to finance its activities without additional subordinated financial support as Tisento Parent is a startup entity in its early stages of raising funds and will require significant capital to advance its programs to commercial stage. Therefore, the Company concluded that its investment in Tisento Parent is a variable interest entity (“VIE”) in accordance with ASC 810-10-15-14(a) and is subject to potential consolidation under the VIE model. However, all activities that most significantly impact Tisento Parent and its subsidiary’s economic performance are directed by the Tisento Parent board and the board approves decisions by a simple majority. Based on the board composition, the Company determined that no one party has control over the Tisento Parent board and power is not shared because the activities that most significantly affect Tisento Parent and its subsidiary’s economic performance do not require the consent of all of the parties. Rather, all decisions are made by a simple majority vote of the Tisento Parent board. Therefore, because the Company controls no director of Tisento Parent, the Company cannot unilaterally direct any of the activities that most significantly impact Tisento Parent and its subsidiary’s economic performance. Accordingly, the Company does not hold a controlling financial interest in Tisento Parent. Because both criteria (a) and (b) above have to be met for the application of the guidance in ASC 810-10-25-44B and criteria (a) has not been met, the Company concluded that it should not consolidate Tisento under the VIE model. Accordingly, the Company has accounted for the investment as a financial instrument without a readily determinable fair value. Such investment is recorded using the measurement alternative for investments without readily determinable fair values, whereby the investment is measured at cost less any impairment recorded or adjustments for observable price changes. An impairment loss is recognized in the consolidated statements of operations and comprehensive loss equal to the amount by which the carrying value exceeds the fair value of the investment. As of March 31, 2026, no impairment loss was recognized. The Company considers the cost of the investment to be the maximum exposure to loss as a result of its involvement with the non-affiliated entity.	4. Other Investment On July 28, 2023, the Company closed the transactions contemplated by the Asset Purchase Agreement receiving proceeds of $8.0 million as cash consideration, approximately $2.4 million as reimbursement for certain operating expenses related to zagociguat and CY3018 programs for the period between signing and closing of the transaction, and 10% of all of Tisento Parent’s outstanding equity securities which fair value was determined to be $5.3 million at the time of closing. The Company’s investment in Tisento Parent does not provide it with significant influence over Tisento Parent. The Company has determined that the Company’s investment in Tisento Parent is an equity security, whereby such investment does not give the Company a controlling financial interest or significant influence over the investee. Further, the Company assessed the accounting for its investment in Tisento Parent in accordance with ASC 810-10, Consolidation—Overall. After determining that no scope exception applies under the guidance of ASC 810-10-15-12 and ASC 810-10-15-17, the Company concluded that it has a variable interest in Tisento Parent through its investment in Tisento Parent common stock. Tisento Parent does not have sufficient equity to finance its activities without additional subordinated financial support as Tisento Parent is a startup entity in its early stages of raising funds and will require significant capital to advance its programs to commercial stage. Therefore, the Company concluded that its investment in Tisento Parent is a variable interest entity (“VIE”) in accordance with ASC 810-10-15-14(a) and is subject to potential consolidation under the VIE model. However, all activities that most significantly impact Tisento Parent and its subsidiary’s economic performance are directed by the Tisento Parent board and the board approves decisions by a simple majority. Based on the board composition, the Company determined that no one party has control over the Tisento Parent board and power is not shared because the activities that most significantly affect Tisento Parent and its subsidiary’s economic performance do not require the consent of all of the parties. Rather, all decisions are made by a simple majority vote of the Tisento Parent board. Therefore, because the Company controls no director of Tisento Parent, the Company cannot unilaterally direct any of the activities that most significantly impact Tisento Parent and its subsidiary’s economic performance. Accordingly, the Company does not hold a controlling financial interest in Tisento Parent. Because both criteria (a) and (b) above have to be met for the application of the guidance in ASC 810-10-25-44B and criteria (a) has not been met, The Company concluded that it should not consolidate Tisento under the VIE model. Accordingly, the Company has accounted for the investment as a financial instrument without a readily determinable fair value. Such investment is recorded using the measurement alternative for investments without readily determinable fair values, whereby the investment is measured at cost less any impairment recorded or adjustments for observable price changes. An impairment loss is recognized in the consolidated statements of operations and comprehensive loss equal to the amount by which the carrying value exceeds the fair value of the investment. As of December 31, 2025, no impairment loss was recognized. The Company considers the cost of the investment to be the maximum exposure to loss as a result of its involvement with the non-affiliated entity. The initial fair value of the investment in Tisento Parent was determined by reference to the risk-adjusted net assets value using the discounted cash flow method. The estimated net assets value of Tisento Parent includes the cash generated/used from the operations and the proceeds from equity financing. Valuations were derived by reference to observable valuation measures for comparable companies or transactions, including weighted average cost of capital (21% to 23%), terminal decline rate (25% to 75%) and the discount rate referenced by a two-year treasury rate of 4.01%.

Share-based Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Restricted Stock Awards
Share-based Compensation Plans
Expected period to recognize the expense	1 year 5 months 12 days
Unrecognized share-based compensation expense	$ 200
Granted (in shares)	0	0	0	65,000
Restricted Stock Awards \| Director
Share-based Compensation Plans
Expected period to recognize the expense			1 year 8 months 8 days
Unrecognized share-based compensation expense			$ 200
Performance stock options
Share-based Compensation Plans
Number of shares vested	0	0	0	0
Share based compensation expense	$ 0	$ 0	$ 0	$ 0
Employee Stock Option
Share-based Compensation Plans
Unrecognized share-based compensation expense	$ 100
Expected period to recognize the expense	2 years 10 months 9 days		3 years 10 days
Weighted average grant date fair value per option share			$ 2.14	$ 2.8
Total intrinsic value	$ 0	$ 0	$ 0	$ 0
Unrecognized share-based compensation expense			$ 100
Granted (in shares)	0		25,000	55,849

Income Taxes - Reconciliation of income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Effective Income Tax Rate Reconciliation [Line Items]
Pretax loss	$ (3,528)	$ (3,058)
US Federal Statutory Tax Rate	(741)	(642)
Foreign tax effects	0	(1)
Non-deductible items	571	88
Tax credits	0	(11)
Change in valuation allowance	170	566
Income Tax Expense (Benefit), Total	$ 0	$ 0
US Federal Statutory Tax Rate, Percent	21.00%	21.00%
Foreign tax effects, Percent	0.00%	0.00%
Non-deductible items, Percent	16.20%	2.90%
Tax credits, Percent	0.00%	0.40%
Change in valuation allowance, Percent	4.80%	18.50%
Income Tax Expense (Benefit), Percent, Total	0.00%	0.00%

Other Investment - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
	Jul. 28, 2023	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Investment Holdings, Other than Securities [Line Items]
Cash consideration transferrred	$ 8,000
Operating expenses	$ 2,400	$ 3,209	$ 1,538	$ 7,047	$ 5,628
Impairment loss on other investments		$ 0		$ 0
Tisento Therapeutics Holdings Inc
Investment Holdings, Other than Securities [Line Items]
Outstanding equity securities	10.00%
Fair value of outstanding equity securities	$ 5,300
Treasury rate
Investment Holdings, Other than Securities [Line Items]
Net assets percentage	4.01%
Minimum \| Weighted average investment
Investment Holdings, Other than Securities [Line Items]
Net assets percentage	21.00%
Minimum \| Terminal decline rate
Investment Holdings, Other than Securities [Line Items]
Net assets percentage	25.00%
Maximum \| Weighted average investment
Investment Holdings, Other than Securities [Line Items]
Net assets percentage	23.00%
Maximum \| Terminal decline rate
Investment Holdings, Other than Securities [Line Items]
Net assets percentage	75.00%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2025

Income Tax Disclosure [Abstract]

The components of net income (loss) before income tax expense are as follows (in thousands):


	Year Ended December 31,
	2025			2024
Domestic	$	(3,528	)	$	(3,061	)
Foreign		—			3

Total	$	(3,528	)	$	(3,058	)

Summary of reconciliation of income taxes computed using the U.S. federal statutory rate

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations follows after adoption of ASU

2023-09

on a retrospective basis (in thousands):


	Year Ended December 31,
	2025						2024
	Amount			Percent			Amount			Percent
Pretax loss	$	(3,528	)				$	(3,058	)
US Federal Statutory Tax Rate		(741	)		21.0	%		(642	)		21.0	%
Foreign tax effects		—			—			(1	)		0.0	%
Non-deductible items		571			-16.2	%		88			-2.9	%
Tax credits		—			—			(11	)		0.4	%
Change in valuation allowance		170			-4.8	%		566			-18.5	%

	$	—			0.0	%	$	—			0.0	%

Summary of deferred tax assets (liabilities)

Deferred tax assets (liabilities) consist of the following as of December 31, 2025 and 2024 (in thousands):


	Year Ended December 31,
	2025			2024
Deferred tax assets:
Net operating loss carryforwards	$	57,618		$	53,281
Tax credit carryforwards		10,385			10,383
Share-based compensation		6,500			7,122
Capitalized research and development		8,867			12,370
Intangibles		20			—

Total deferred tax assets	$	83,390		$	83,156

Valuation allowance		(83,390	)		(83,156	)

Net deferred tax assets	$	—		$	—

Income Taxes - Schedule of Components of Net Income Loss Before Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest [Abstract]
Domestic	$ (3,528)	$ (3,061)
Foreign	0	3
Total	$ (3,528)	$ (3,058)

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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License and Option Agreement	3 Months Ended	12 Months Ended
License and Option Agreement	Mar. 31, 2026	Dec. 31, 2025
License Agreement [Abstract]
License and Option Agreement	9. Option/License Agreement Patent License Agreement On September 19, 2025, the Company and MIT entered into a Patent License Agreement (the “MIT License Agreement”) pursuant to which MIT granted to the Company an exclusive worldwide license to develop and commercialize products using certain technology for the treatment of neuropsychiatric disorders, such as depression, in humans. Under the MIT License Agreement, the Company paid a nominal upfront license fee and patent reimbursement fee. Thereafter, the Company is also required to pay MIT a nominal annual license maintenance fee. This annual license maintenance fee is nonrefundable; however, the license maintenance fee may be credited to royalties earned during the same calendar year, if any. License maintenance fees paid in excess of royalties due in such calendar year shall not be creditable to amounts due for future years. Under the terms of the MIT License Agreement, MIT will be eligible to receive up to $4.4 million upon the achievement of certain development, regulatory and sales milestone payments. MIT will also receive tiered royalties in a range of percentages in the low single digits based on future net sales of licensed products as set forth in the MIT License Agreement. Further, the Company is required to pay MIT varying percentages of income received as consideration for any sublicenses granted pursuant to the MIT License Agreement depending on the circumstances of the sublicense and the development milestones of sublicensed products. The term of the MIT License Agreement will expire in its entirety upon the expiration of certain patent rights for the licensed patents, unless earlier terminated by the parties in accordance with the terms of the MIT License Agreement. No expense was recognized for the three months ended March 31, 2026 and 2025 related to the license. Akebia License Agreement On June 3, 2021, the Company and Akebia entered into a License Agreement (the “Akebia License Agreement”) relating to the exclusive worldwide license by the Company to Akebia of its rights to the development, manufacture, medical affairs and commercialization of pharmaceutical products containing the pharmaceutical compound known as praliciguat and other related products and forms thereof enumerated in the License Agreement (collectively, the “Products”). Pursuant to the Akebia License Agreement, Akebia will be responsible for all future research, development, regulatory, and commercialization activities for the Products. Akebia paid a $3.0 million up-front payment to the Company upon signing of the License Agreement. On December 13, 2024, the Company and Akebia entered into Amendment #1 to the License Agreement (the “2024 Amendment”) to the original License Agreement between the parties dated June 3, 2021. Under the terms of the 2024 Amendment, Akebia paid $1.75 million in amendment payments, of which $1.25 million was paid in December 2024 and an additional payment of $0.5 million was paid in September 2025. In addition, Akebia has agreed to assume control of the preparation, filing, prosecution and maintenance of certain Cyclerion patents, and the expenses associated therewith, at an earlier date than as originally agreed between the parties. The parties have agreed to the reduction of certain development milestones and the increase of certain royalty rates on net sales and sublicense income. On December 1, 2025, Akebia publicly announced that it has recently initiated Phase 2 clinical trials for the treatment of focal segmental glomerulosclerosis (“FSGS”) using praliciguat. Pursuant to the terms of amendment, upon initiation of a Phase 2 clinical trial in the U.S. for a product, a $1.0 million development milestone payment would be due to the Company and which was received in February 2026. Pursuant to the terms of the Akebia License Agreement, as amended, Cyclerion is eligible to receive additional potential future development, regulatory, and commercialization milestone payments up to $557.5 million in total, and Akebia will pay Cyclerion tiered royalties ranging from mid-single digit to twenty percent of net sales. Cyclerion’s obligations to deliver certain drug products have also ceased. Pursuant to the Akebia License Agreement, the Company determined the Akebia License Agreement represents a service arrangement under the scope of ASC 606. Given the reversion of the rights under the Akebia License Agreement represents a penalty in substance for a termination by Akebia, the contract term would be the stated term of the License Agreement. The Company determined that the grant of license to its patents and trademarks, know how transfer, the assignment of regulatory submissions and trademarks and additional knowledge transfer assistance obligations represent a single promise and performance obligation to be transferred to Akebia over time due to the nature of the promises in the contract. The provision of development materials on hand was identified as a separate performance obligation. However, it is immaterial in the context of the contract as the development materials are low value and do not have an alternative use to the Company. The consideration related to sales-based milestone payments, including royalties, will be recognized when the related sales occur as these amounts have been determined to relate predominantly to the license. The Company will re-evaluate the probability of achievement of the milestones and any related constraints each reporting period. Akebia Material Purchase Agreement On September 3, 2025, the Company and Akebia entered into a Material Purchase Agreement (the “Purchase Agreement”) relating to the purchase of additional development materials (the “Additional Development Materials”) by Akebia for Akebia’s use pursuant to the Akebia License Agreement. Akebia paid $0.8 million to the Company for the purchase during the year ended December 31, 2025 and the Additional Development Materials were delivered to Akebia as of December 31, 2025. The Company determined the Purchase Agreement has stand-alone value under the scope of ASC 606 and should not be combined with the Akebia License Agreement or the Amendment. The delivery of the Additional Development Materials by the Company represents a single performance obligation and consideration was recognized upon delivery. No revenue was recognized under the Purchase Agreement during three months ended March 31, 2026 and 2025. Option Agreement On July 22, 2024, the Company entered into an Option to License Agreement (the “Option Agreement”) with a third party (the “Optionee”), pursuant to which the Optionee had an option (the “Option”) to enter into an exclusive license to olinciguat for human therapeutics, subject to certain carveouts. Under the terms of the Option Agreement, the Optionee paid the Company an Option fee of $150,000 in August 2024 and subsequent fees totaling $80,000 to extend the term of the Option Agreement. The Optionee originally could exercise the Option on or before March 20, 2025, which option period was ultimately extended through August 22, 2025. Thereafter, the parties had an additional 60 days to negotiate the terms of a definitive license agreement. The parties were unable to agree upon the terms of a license agreement and the Company provided notice on October 23, 2025 that it was terminating the Option Agreement. The Company recognized revenue of $0.1 million related to the extension fee payment and expense reimbursement for the three months ended March 31, 2025. Medsteer Collaboration Agreement On January 3, 2026, the Company and the Medsteer, SAS (“Medsteer”) entered into a Collaboration and Option Agreement (the “Collaboration Agreement”) pursuant to which Medsteer granted to the Company (i) a non-exclusive, worldwide, royalty-free, sublicensable license of certain of Medsteer’s technology, software and intellectual property to develop an anesthetic delivery system with Medsteer and (ii) an exclusive option (the “Option”), exercisable at the Company’s sole discretion, to obtain an exclusive, worldwide, royalty-bearing, sublicensable license of certain of Medsteer’s technology, software and intellectual property to develop or commercialize licensed products in any field of use except for sedation regulation for patients undergoing major surgery, in multi-bed or intensive unit wards, or in the context of medical transport. The Company may exercise the Option at any time until the earlier of the second anniversary of the effective date of the Collaboration Agreement, which period may be extended for an additional two years at the Company’s option and upon payment of a nominal fee or by mutual agreement of the Company and Medsteer. Under the terms of the Collaboration Agreement, the Company recognized $0.1 million research and development expense during the three months ended March 31, 2026, which is related to the upfront payment paid to Medsteer and other transaction costs. Medsteer will be eligible to receive up to $3.7 million upon the achievement of certain development, regulatory and sales milestone payments. Medsteer will also receive an annual royalty payment and royalties in a percentage in the low single digits based on future net sales of licensed products, subject to certain adjustments as set forth in the Collaboration Agreement.	11. License and Option Agreement Patent License Agreement On September 19, 2025, the Company and MIT entered into a Patent License Agreement (the “MIT License Agreement”) pursuant to which MIT granted to the Company an exclusive worldwide license to develop and commercialize products using certain technology for the treatment of neuropsychiatric disorders, such as depression, in humans. Under the MIT License Agreement, the Company paid a nominal upfront license fee and patent reimbursement fee. Thereafter, the Company is also required to pay MIT a nominal annual license maintenance fee. This annual license maintenance fee is nonrefundable; however, the license maintenance fee may be credited to royalties earned during the same calendar year, if any. License maintenance fees paid in excess of royalties due in such calendar year shall not be creditable to amounts due for future years. Under the terms of the MIT License Agreement, MIT will be eligible to receive up to $4.4 million upon the achievement of certain development, regulatory and sales milestone payments. MIT will also receive tiered royalties in a range of percentages in the low single digits based on future net sales of licensed products as set forth in the MIT License Agreement. Further, the Company is required to pay MIT varying percentages of income received as consideration for any sublicenses granted pursuant to the MIT License Agreement depending on the circumstances of the sublicense and the development milestones of sublicensed products. The term of the MIT License Agreement will expire in its entirety upon the expiration of certain patent rights for the licensed patents, unless earlier terminated by the parties in accordance with the terms of the MIT License Agreement. The Company recorded research and development expense of $0.1 million for the year ended December 31, 2025, which consisted of upfront fees, patent reimbursement fees and transaction costs related to the license. Akebia License Agreement On June 3, 2021, the Company and Akebia entered into a License Agreement (the “Akebia License Agreement”) relating to the exclusive worldwide license by the Company to Akebia of its rights to the development, manufacture, medical affairs and commercialization of pharmaceutical products containing the pharmaceutical compound known as praliciguat and other related products and forms thereof enumerated in the License Agreement (collectively, the “Products”). Pursuant to the Akebia License Agreement, Akebia will be responsible for all future research, development, regulatory, and commercialization activities for the Products. Akebia paid a $3.0 million up-front payment to the Company upon signing of the License Agreement. On December 13, 2024, the Company and Akebia entered into Amendment #1 to the License Agreement (the “2024 Amendment”) to the original License Agreement between the parties dated June 3, 2021. Under the terms of the 2024 Amendment, Akebia paid $1.75 million in amendment payments, of which $1.25 million was paid in December 2024 and an additional payment of $0.5 million was paid in September 2025. In addition, Akebia has agreed to assume control of the preparation, filing, prosecution and maintenance of certain Cyclerion patents, and the expenses associated therewith, at an earlier date than as originally agreed between the parties. The parties have agreed to the reduction of certain development milestones and the increase of certain royalty rates on net sales and sublicense income. On December 1, 2025, Akebia publicly announced that it has recently initiated Phase 2 clinical trials for the treatment of focal segmental glomerulosclerosis (“FSGS”) using praliciguat. Pursuant to the terms of amendment, upon initiation of a Phase 2 clinical trial in the U.S. for a product, a $1.0 million development milestone payment would be due to the Company and which was received in February 2026. Pursuant to the terms of the Akebia License Agreement, as amended, Cyclerion is eligible to receive additional potential future development, regulatory, and commercialization milestone payments up to $557.5 million in total, and Akebia will pay Cyclerion tiered royalties ranging from mid-single digit to twenty percent of net sales. Cyclerion’s obligations to deliver certain drug products have also ceased. Pursuant to the Akebia License Agreement, the Company determined the Akebia License Agreement represents a service arrangement under the scope of ASC 606. Given the reversion of the rights under the Akebia License Agreement represents a penalty in substance for a termination by Akebia, the contract term would be the stated term of the License Agreement. The Company determined that the grant of license to its patents and trademarks, know how transfer, the assignment of regulatory submissions and trademarks and additional knowledge transfer assistance obligations represent a single promise and performance obligation to be transferred to Akebia over time due to the nature of the promises in the contract. The provision of development materials on hand was identified as a separate performance obligation. However, it is immaterial in the context of the contract as the development materials are low value and do not have an alternative use to the Company. The consideration related to sales-based milestone payments, including royalties, will be recognized when the related sales occur as these amounts have been determined to relate predominantly to the license. The Company will re-evaluate the probability of achievement of the milestones and any related constraints each reporting period. Akebia Material Purchase Agreement On September 3, 2025, the Company and Akebia entered into a Material Purchase Agreement (the “Purchase Agreement”) relating to the purchase of additional development materials (the “Additional Development Materials”) by Akebia for Akebia’s use pursuant to the Akebia License Agreement. Akebia paid $0.8 million to the Company for the purchase during the year ended December 31, 2025 and the Additional Development Materials were delivered to Akebia as of December 31, 2025. The Company determined the Purchase Agreement has stand-alone value under the scope of ASC 606 and should not be combined with the Akebia License Agreement or the Amendment. The delivery of the Additional Development Materials by the Company represents a single performance obligation and consideration was recognized upon delivery. The Company recognized revenue of $0.8 million during the year ended December 31, 2025. Option Agreement On July 22, 2024, the Company entered into an Option to License Agreement (the “Option Agreement”) with a third party (the “Optionee”), pursuant to which the Optionee had an option (the “Option”) to enter into an exclusive license to olinciguat for human therapeutics, subject to certain carveouts. Under the terms of the Option Agreement, the Optionee paid the Company an Option fee of $150,000 in August 2024 and subsequent fees totaling $80,000 to extend the term of the Option Agreement. The Optionee originally could exercise the Option on or before March 20, 2025, which option period was ultimately extended through August 22, 2025. Thereafter, the parties had an additional 60 days to negotiate the terms of a definitive license agreement. The parties were unable to agree upon the terms of a license agreement and the Company provided notice on October 23, 2025 that it was terminating the Option Agreement.

License and Option Agreement - Additional Information (Details) - USD ($)					1 Months Ended		3 Months Ended		9 Months Ended	12 Months Ended
	Jan. 03, 2026	Sep. 19, 2025	Jul. 22, 2024	Jun. 03, 2021	Feb. 28, 2026	Aug. 31, 2024	Mar. 31, 2026	Mar. 31, 2025	Sep. 30, 2025	Dec. 31, 2025	Dec. 31, 2024
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense							$ 730,000	$ 36,000		$ 959,000	$ 286,000
Option fee						$ 150,000
Option additional fee			$ 80,000
Revenue recognized								100,000
Revenues							0	81,000		2,074,000	2,000,000
Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up front payment received	$ 3,700,000
Patent License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense										100,000
Revenue recognized		$ 4,400,000
Costs and Expenses							0			0
Akebia Research License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up front payment received				$ 3,000,000
Amendment Akebia Research License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up front payment received				$ 1,750,000							$ 1,250,000
Additional up front payment									$ 500,000
Commercialization milestone payments										557,500,000
Amendment Akebia Research License Agreement [Member] \| Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development milestone payment					$ 1,000,000
Akebia Material Purchase Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of additional development materials										800,000
Revenues							0	$ 0		$ 800,000
Medsteer Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense							$ 100,000
Revenue recognized	$ 3,700,000

Defined Contribution Plan	12 Months Ended
Defined Contribution Plan	Dec. 31, 2025
Retirement Benefits [Abstract]
Defined Contribution Plan	10. Defined Contribution Plan The Company has established a defined contribution 401(k) Savings Plan which allows eligible employees to contribute from 1% to 100% of their compensation, subject to certain IRS limits. The Company’s contributions to the plan are at the sole discretion of the board of directors. Currently, the Company provides a matching contribution of 75% of the employee’s contributions, up to $6,000 annually. Included in compensation expense is de minimis related to the defined contribution 401(k) Savings Plan for the years ended December 31, 2025 and 2024, respectively.

The entire disclosure for retirement benefits.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Variable Interest Entities

Cover Page	3 Months Ended
Cover Page	Mar. 31, 2026
Document Information [Line Items]
Entity Registrant Name	CYCLERION THERAPEUTICS, INC.
Document Type	S-4/A
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Central Index Key	0001755237
Amendment Flag	false
Entity Tax Identification Number	83-1895370
Entity Incorporation, State or Country Code	MA
Entity Address, Address Line One	245 First Street, 18th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	857
Local Phone Number	327-8778
Entity Primary SIC Number	2834
Business Contact [Member]
Document Information [Line Items]
Entity Address, Address Line One	245 First Street, 18th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	857
Local Phone Number	327-8778
Contact Personnel Name	Regina Graul, Ph.D.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Accounting Policies [Abstract]

Basis of Presentation

The condensed consolidated financial statements and the related disclosures are unaudited and have been prepared in accordance with accounting principles generally accepted in the U.S. Additionally, certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form

10-K

for the fiscal year ended December 31, 2025, which was filed with the SEC on March 30, 2026.

Basis of Presentation

The consolidated financial statements and the related disclosures have been prepared in accordance with U.S. generally accepted accounting principles. In the opinion of management, the consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the fiscal years presented.

The consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries, Cyclerion Securities Corporation and Cyclerion GmbH which was dissolved in May 2024. All significant intercompany accounts and transactions have been eliminated in the preparation of the accompanying consolidated financial statements.

Segment Information

non-operating

expenses and operating expenses excluding

non-cash

stock based compensation expense.

Investment

Use of Estimates

The preparation of consolidated financial statements in accordance with U.S. generally accepted

accounting

which they become known.

Cash and Cash Equivalents

Fair Value of Investment Instruments

•

Level 1 — Quoted prices in active markets for identical assets or liabilities.

•

Foreign Currency Translation Adjustment

The Company’s intercompany accounts are typically denominated in the functional currency of the foreign subsidiary. Gains and losses resulting from the

re-measurement

of intercompany balances are recorded in the consolidated statements of operations.

Accounts Receivable

significant outstanding invoices. The Company believes that credit risks associated with these agreements are not significant. To date, the Company has not had

significant

write-offs of bad debt and the Company did not have an allowance for doubtful accounts as of December 31, 2025 or 2024.

Revenue

Revenue from Contracts with Customers

License and Option Agreement

Research and Development Costs

General and Administrative Expenses

Income taxes

The tax positions taken or expected to be taken in the course of preparing the Company tax returns are required to be evaluated to determine whether the tax positions are

“more-likely-than-not”

of being sustained by the applicable tax authority. Tax positions not deemed to meet a

more-likely-than-not

Patent Costs

Interest and Other Income, Net

Subsequent Events

10-K.

See Note 12,

Subsequent Events

Recently Issued/Adopted Accounting Pronouncements

New Accounting Pronouncements

Recently Issued Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Except as discussed elsewhere in the notes to the consolidated financial statements, the Company did not adopt any new accounting pronouncements during the years ended December 31, 2025 and 2024, that had a material effect on its consolidated financial statements.

In August 2025, the FASB issued ASU

No. 2025-05,

Recently Adopted Accounting Pronouncements

In November 2023, the FASB issued ASU

No. 2023-07,

In December 2023, the FASB issued ASU

No. 2023-09,

Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which focuses on the rate reconciliation and income taxes paid. ASU

No. 2023-09

pre-ASU

Loss per share (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Net Loss Per Common Share

Basic and diluted net loss per common share is computed by dividing net loss by the weighted average number of common shares outstanding during the period as follows:


	Three Months Ended March 31,
	2026			2025
Numerator:
Net loss (in thousands)	$	(3,177	)	$	(1,429	)
Denominator:
Weighted average shares used in calculating net loss per share — basic and diluted (in thousands)		4,205			2,556

Net loss per share — basic and diluted	$	(0.76	)	$	(0.56	)

Basic and diluted net loss per common share is computed by dividing net loss by the weighted average number of common shares outstanding during the period as follows:


	Year Ended December 31,
	2025			2024
Numerator:
Net loss (in thousands)	$	(3,528	)	$	(3,057	)
Denominator:
Weighted average shares used in calculating net loss per share — basic and diluted (in thousands)		3,181			2,518

Net loss per share — basic and diluted	$	(1.11	)	$	(1.21	)

Schedule of earnings per share diluted by common class

The following table sets forth potential shares that were considered anti-dilutive for the three months ended March 31, 2026 and 2025:


	Three Months Ended March 31,
	2026		2025
Preferred Stock		351,037		351,037
Stock Options		280,407		329,458
RSAs		89,054		149,150

		720,498		829,645

The following table sets forth potential shares that were considered anti-dilutive for the years ended December 31, 2025 and 2024:


	Year Ended December 31,
	2025		2024
Preferred Stock		351,037		351,037
Stock Options		297,762		335,448
RSAs		104,078		164,174

		752,877		850,659

Income Taxes - Deferred tax assets (liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Deferred tax assets:
Net operating loss carryforwards	$ 57,618	$ 53,281
Tax credit carryforwards	10,385	10,383
Share-based compensation	6,500	7,122
Capitalized research and development	8,867	12,370
Intangibles	20	0
Total deferred tax assets	83,390	83,156
Valuation allowance	(83,390)	(83,156)
Net deferred tax assets	$ 0	$ 0

Subsequent Events (Additional Information) (Details) - USD ($) $ in Thousands			3 Months Ended		12 Months Ended
	Jan. 06, 2026	Jan. 03, 2026	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Subsequent Event [Line Items]
Common stock, shares issued			4,330,314		3,925,314	2,710,096
Proceeds from stock purchase agreement			$ 0	$ 1,375	$ 1,375	$ 0
Subsequent Event [Member]
Subsequent Event [Line Items]
Common stock, shares issued	405,000
Proceeds from stock purchase agreement	$ 800
Exercise period		The Company may exercise the Option at any time until the earlier of the second anniversary of the effective date of the Collaboration Agreement, which period may be extended for an addition two years at the Company’s option and upon payment of a nominal fee or by mutual agreement of the Company and Medsteer.
Up front payment received		$ 3,700

Fair Value of Financial Instruments (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Fair Value Disclosures [Abstract]

Schedule of financial assets measured at fair value on a recurring basis and indicating the level of the fair value hierarchy


	Fair Value Measurements as of March 31, 2026:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	2,610	$	—	$	—	$	2,610

Cash equivalents	$	2,610	$	—	$	—	$	2,610


	Fair Value Measurements as of December 31, 2025:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	3,072	$	—	$	—	$	3,072

Cash equivalents	$	3,072	$	—	$	—	$	3,072

The Company’s cash equivalents are generally classified within Level 1 of the fair value hierarchy. The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values as of December 31, 2025 and December 31, 2024 (in thousands):


	Fair Value Measurements as of December 31, 2025:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	3,072	$	—	$	—	$	3,072

Cash equivalents	$	3,072	$	—	$	—	$	3,072


	Fair Value Measurements as of December 31, 2024:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	3,025	$	—	$	—	$	3,025

Cash equivalents	$	3,025	$	—	$	—	$	3,025

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended
	Aug. 31, 2024	May 31, 2024	Dec. 31, 2025	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Payment to former chief financial officer	$ 100,000	$ 100,000
Separation benefits obligation			$ 0	$ 0
Liabilities recorded for indemnification provisions			$ 0	$ 0

Commitments and Contingencies	3 Months Ended	12 Months Ended
Commitments and Contingencies	Mar. 31, 2026	Dec. 31, 2025
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Other Funding Commitments In the normal course of business, the Company enters into contracts with clinical research organizations and other third parties for clinical and preclinical research studies and other services and products for operating purposes. These contracts are generally cancellable, with notice, at the Company’s option and do not have any significant cancellation penalties. Indemnification Obligations On September 6, 2018, Cyclerion was incorporated in Massachusetts and its officers and directors are indemnified for certain events or occurrences while they are serving in such capacity. The Company enters into certain agreements with other parties in the ordinary course of business that contain indemnification provisions. These typically include agreements with directors and officers, business partners, contractors, clinical sites and customers. Under these provisions, the Company generally indemnifies and holds harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of the Company’s activities. These indemnification provisions generally survive termination of the underlying agreements. The maximum potential amount of future payments the Company could be required to make under these indemnification provisions is unlimited . However, to date the Company has not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these obligations is minimal. Accordingly, the Company did not have any liabilities recorded for these obligations as of March 31, 2026 and December 31, 2025.	6. Commitments and Contingencies Other Funding Commitments The Company may enter into contracts with clinical research organizations and other third parties for clinical and preclinical research studies and other services and products for operating purposes. These contracts are generally cancellable, with notice, at the Company’s option and do not have any significant cancellation penalties. Guarantees On September 6, 2018, Cyclerion was incorporated in Massachusetts and its officers and directors are indemnified for certain events or occurrences while they are serving in such capacity. The Company enters into certain agreements with other parties in the ordinary course of business that contain indemnification provisions. These typically include agreements with directors and officers, business partners, contractors, clinical sites and customers. Under these provisions, the Company generally indemnifies and holds harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of the Company’s activities. These indemnification provisions generally survive termination of the underlying agreements. The maximum potential amount of future payments the Company could be required to make under these indemnification provisions is unlimited. However, to date the Company has not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these obligations is minimal. Accordingly, the Company did not have any liabilities recorded for these obligations as of December 31, 2025 or December 31, 2024. Separation Benefits As part of the separation benefit of the former Chief Financial Officer, the Company paid $0.1 million each in May 2024 and August 2024. The Company has no further separation benefits obligation as of December 31, 2025 and 2024.

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Current assets:
Cash and cash equivalents	$ 2,823	$ 3,240	$ 3,232
Accounts receivable	0	1,000	556
Prepaid expenses	255	384	421
Other current assets	11	11	16
Total current assets	3,089	4,635	4,225
Property and equipment, net	66	0
Other investment	5,350	5,350	5,350
Total assets	8,505	9,985	9,575
Current liabilities:
Accounts payable	457	508	390
Accrued research and development costs	148	198	52
Accrued expenses and other current liabilities	1,109	194	283
Total current liabilities	1,714	900	725
Commitments and contingencies (Note 6)	0	0	0
Stockholders' equity
Preferred stock, no par value, 100,000,000 shares authorized and 351,037 shares of Series A convertible preferred stock issued and outstanding at March 31, 2026 and December 31, 2025	0	0	0
Common stock, no par value, 400,000,000 shares authorized at March 31, 2026 and December 31, 2025; 4,330,314 and 3,925,314 shares issued at March 31, 2026 and December 31, 2025, respectively; 4,241,260 and 3,821,236 shares outstanding at March 31, 2026 and December 31, 2025, respectively	0	0	0
Paid-in capital	280,988	280,105	276,342
Accumulated deficit	(274,197)	(271,020)	(267,492)
Total stockholders' equity	6,791	9,085	8,850
Total liabilities and stockholders' equity	$ 8,505	$ 9,985	$ 9,575

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Revenues:
Total revenues	$ 0	$ 81	$ 2,074	$ 2,000
Cost and expenses:
Research and development	730	36	959	286
General and administrative	2,479	1,502	6,088	5,342
Total cost and expenses	3,209	1,538	7,047	5,628
Loss from operations	(3,209)	(1,457)	(4,973)	(3,628)
Other income, net
Interest income	32	28	128	208
Gain from settlement of account payable			0	363
Gain from insurance recovery			1,317	0
Total other income, net	32	28	1,445	571
Net loss	$ (3,177)	$ (1,429)	$ (3,528)	$ (3,057)
Net loss per share:
Net loss per share - Basic	$ (0.76)	$ (0.56)	$ (1.11)	$ (1.21)
Net loss per share - Diluted	$ (0.76)	$ (0.56)	$ (1.11)	$ (1.21)
Weighted average shares used in calculating:
Basic shares	4,205	2,556	3,181	2,518
Diluted shares	4,205	2,556	3,181	2,518
Other comprehensive loss:
Net loss	$ (3,177)	$ (1,429)	$ (3,528)	$ (3,057)
Other comprehensive loss:
Foreign currency translation adjustment loss			0	(6)
Comprehensive loss			(3,528)	(3,063)
Revenue from license agreement
Revenues:
Total revenues			1,000	1,750
Revenue from purchase agreement
Revenues:
Total revenues			800	0
Revenue from option agreement
Revenues:
Total revenues	$ 0	$ 81	$ 274	$ 250

Income Taxes

12 Months Ended

Dec. 31, 2025

Income Tax Disclosure [Abstract]

Income Taxes

9. Income Taxes

The components of net income (loss) before income tax expense are as follows (in thousands):


	Year Ended December 31,
	2025			2024
Domestic	$	(3,528	)	$	(3,061	)
Foreign		—			3

Total	$	(3,528	)	$	(3,058	)

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations follows after adoption of ASU

2023-09

on a retrospective basis (in thousands):


	Year Ended December 31,
	2025						2024
	Amount			Percent			Amount			Percent
Pretax loss	$	(3,528	)				$	(3,058	)
US Federal Statutory Tax Rate		(741	)		21.0	%		(642	)		21.0	%
Foreign tax effects		—			—			(1	)		0.0	%
Non-deductible items		571			-16.2	%		88			-2.9	%
Tax credits		—			—			(11	)		0.4	%
Change in valuation allowance		170			-4.8	%		566			-18.5	%

	$	—			0.0	%	$	—			0.0	%

The Company’s effective tax rate differs from the statutory rate primarily due to continued losses and the maintenance of a full valuation allowance on deferred tax assets, resulting in zero income tax expense for the period.

Deferred tax assets (liabilities) consist of the following as of December 31, 2025 and 2024 (in thousands):


	Year Ended December 31,
	2025			2024
Deferred tax assets:
Net operating loss carryforwards	$	57,618		$	53,281
Tax credit carryforwards		10,385			10,383
Share-based compensation		6,500			7,122
Capitalized research and development		8,867			12,370
Intangibles		20			—

Total deferred tax assets	$	83,390		$	83,156

Valuation allowance		(83,390	)		(83,156	)

Net deferred tax assets	$	—		$	—

The Company has evaluated the positive and negative evidence bearing upon the possible realization of its deferred tax assets. Management has considered the Company’s history of operating losses, in addition to the expected timing of the reversal of existing temporary differences and concluded, in accordance with the applicable accounting standards, that it is more likely than not that the Company will not realize the benefit of its deferred tax assets. Accordingly, the net deferred tax assets have been fully reserved at December 31, 2025 and December 31, 2024. Management reevaluates the positive and negative evidence on a quarterly basis.

The valuation allowance increased by approximately $0.2 million during the year ended December 31, 2025 primarily due to increases in capitalized research and development expenses, net operating losses, tax credit carryforwards and deferred tax assets related to share-based compensation.

At December 31, 2025 and 2024, Cyclerion has federal net operating loss carryforwards of approximately $211 million and $195 million, respectively, to offset future federal taxable income that will be carried forward indefinitely until utilized. As of December 31, 2025 and 2024, Cyclerion had state net operating loss carryforwards of approximately $212 million and $196 million, respectively, to offset future state taxable income, which will begin to expire in 2039 and will continue to expire through 2045. Cyclerion also had tax credit carryforwards of approximately $10.8 million as of December 31, 2025, to offset future federal and state income taxes. Federal credits begin to expire in 2039 and will continue to expire through 2044. State credits begin to expire in 2034 and continue through 2039.

The Company’s ability to use its operating loss carryforwards and tax credits to offset future taxable income could be subject to restrictions under Section 382 of the U.S. Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”). These potential restrictions may limit the future use of the operating loss carryforwards and tax credits if certain ownership changes described in the Internal Revenue Code occur. Changes in stock ownership may occur that would create these limitations on the Company’s use of the operating loss carryforwards and tax credits. In such a situation, the Company may be required to pay income taxes, even though significant operating loss carryforwards and tax credits exist.

The Company has not as yet conducted a study of its research and development credit carry forwards. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are

being

presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits,

and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated balance sheets or statements of operations if an adjustment were required.

Upon audit, taxing authorities may challenge all or part of an uncertain income tax position. While Cyclerion has no history of tax audits since its inception on a standalone basis, it may be subject to tax audits by federal and state taxing authorities in the future. Accordingly, Cyclerion regularly assesses the outcome of potential examinations in each of the taxing jurisdictions when determining the adequacy of the amount of unrecognized tax benefit recorded. Cyclerion had no unrecognized tax benefits as of December 31, 2025 and 2024. Cyclerion will recognize interest and penalties, if any, related to uncertain tax positions in income tax expense. As of December 31, 2025 and 2024, no interest or penalties have been accrued. There are no current federal or state income tax audits in progress.

The entire disclosure for income tax.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Share-Based Payment Arrangement [Abstract]

Share-based Compensation Plans

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Share-based Compensation Plans

7. Share-based Compensation Plans

In 2019, Cyclerion adopted share-based compensation plans. Specifically, Cyclerion adopted the 2019 Employee Stock Purchase Plan (“2019 ESPP”) and the 2019 Equity Incentive Plan (“2019 Equity Plan”). Under the 2019 ESPP, eligible employees may use payroll deductions to purchase shares of stock in offerings under the plan, and thereby acquire an interest in the future of the Company. The 2019 Equity Plan provides for stock options, restricted stock awards (“RSAs”) and restricted stock units (“RSUs”).

Cyclerion also mirrored two of Ironwood Pharmaceuticals, Inc. (“Ironwood”) existing plans, the Amended and Restated 2005 Stock Incentive Plan (“2005 Equity Plan”) and the Amended and Restated 2010 Employee, Director and Consultant Equity Incentive Plan (“2010 Equity Plan”). These mirror plans were adopted to facilitate the exchange of Ironwood equity awards for Cyclerion equity awards upon the Separation as part of the equity conversion. As a result of the Separation and in accordance with the EMA, employees of both companies retained their existing Ironwood vested options and received a

pro-rata

share of Cyclerion options, regardless of which company employed them post-Separation. For employees that were ultimately employed by Cyclerion, unvested Ironwood options and RSUs were converted to unvested Cyclerion options and RSUs.

The following table provides share-based compensation reflected in the Company’s condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2026 and 2025 (in thousands):


	Three Months Ended March 31,
	2026		2025
Research and development	$	—	$	12
General and administrative		58		102

	$	58	$	114

Stock Options

Stock options granted under the Company’s equity plans generally have a

ten-year

term and vest over a period of four years, provided the individual continues to serve at the Company through the vesting dates. Options granted under all equity plans are exercisable at a price per share not less than the fair market value of the underlying common stock on the date of grant. The estimated fair value of options, including the effect of estimated forfeitures, is recognized over the requisite service period, which is typically the vesting period of each option.

A summary of stock option activity for the three months ended March 31, 2026, is as follows:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Average Intrinsic Value (in thousands)
Outstanding as of December 31, 2025		297,762		$	149.73		4.9	$	—
Granted		—		$	—
Exercised		—		$	—
Cancelled or forfeited		(17,355	)	$	203.65

Outstanding as of March 31, 2026		280,407		$	146.39		4.9	$	—

Exercisable at March 31, 2026		220,760		$	181.20		4.2	$	—

There were no options exercised during the three months ended March 31, 2026 and 2025. As of March 31, 2026, the unrecognized share-based compensation expense, net of estimated forfeitures, related to all unvested time-based stock options is $0.1 million and the weighted average period over which that expense is expected to be recognized is 2.86 years.

The Company has granted certain former employees performance-based options to purchase shares of common stock. These options are subject to performance-based milestone vesting. During the three months ended March 31, 2026 and 2025, there were no shares that vested as a result of performance milestone achievements. No share-based compensation expense related to these performance-based options was recognized during the three months ended March 31, 2026 and 2025, respectively.

Restricted Stock Awards

No RSA was granted during the three months ended March 31, 2026 and 2025. The fair value of all RSAs is based on the market value of the Company’s common stock on the date of grant. Compensation expense, including the effect of estimated forfeitures, is recognized over the applicable service period.

A summary of RSA activity for the three months ended March 31, 2026 is as follows:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested as of December 31, 2025		104,078		$	2.57
Granted		—			—
Vested		(15,024	)		2.52
Forfeited		—			—

Unvested as of March 31, 2026		89,054		$	2.59

As of March 31, 2026, the unrecognized share-based compensation expense, net of estimated forfeitures, related to all unvested RSAs is $0.2 million and the weighted average period over which that expense is expected to be recognized is 1.45 years.

7. Share-based Compensation Plans

Cyclerion also mirrored two of Ironwood Pharmaceuticals, Inc. (“Ironwood”) existing plans, the

Amended

and Restated 2005 Stock Incentive Plan (“2005 Equity Plan”) and the Amended and Restated 2010 Employee,

Director and Consultant Equity Incentive Plan (“2010 Equity Plan”). These mirror plans were adopted to facilitate the exchange of Ironwood equity awards for Cyclerion equity awards upon the Separation as part of the equity conversion. As a result of the Separation and in accordance with the EMA, employees of both companies retained their existing Ironwood vested options and received a

pro-rata

The following table provides share-based compensation reflected in the Company’s consolidated statements of operations and comprehensive loss for the years ended December 31, 2025 and 2024 (in thousands):


	Year Ended December 31,
	2025		2024
Research and development	$	29	$	91
General and administrative		412		534

	$	441	$	625

Stock Options

Stock options granted under the Company’s equity plans generally have a

ten-year

A summary of stock option activity for the year ended December 31, 2025 is as follows:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Average Intrinsic Value (in thousands)
Outstanding as of December 31, 2024		335,448		$	158.98		4.7	$	—
Granted		25,000		$	2.36
Exercised		—		$	—
Cancelled or forfeited		(62,686	)	$	140.44

Outstanding as of December 31, 2025		297,762		$	149.73		4.9	$	—

Exercisable at December 31, 2025		232,385		$	187.20		4.0	$	—

During the years ended December 31, 2025 and 2024, the Company granted stock options to purchase an aggregate of 25,000 shares and 55,849 shares, respectively, at weighted average grant date fair values per option share of $2.14 and $2.80 respectively.

There were no options exercised during the year ended December 31, 2025 and 2024.

As of December 31, 2025, the unrecognized share-based compensation expense, net of estimated forfeitures, related to all unvested time-based stock options held by the Company’s employee and

non-employees

is $0.1 million and the weighted average period over which that expense is expected to be recognized is 3.03 years.

The weighted-average Black-Scholes assumptions used in estimating the fair value of the stock options granted by Cyclerion during the years ended December 31, 2025 and 2024 were as follows:


	Year ended December 31,
	2025			2024
Weighted average risk-free interest rate		3.79	%		3.64	%
Expected dividend yield		—			—
Expected option term (in years)		5.4			6.0
Expected stock price volatility		141.07	%		111.97	%

For the years ended December 31, 2025 and 2024, expected volatility was estimated using an average of the historical volatility of the common stock of a group of similar companies that were publicly traded. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available.

The Company has granted certain employees performance-based options to purchase shares of common stock. These options are subject to performance-based milestone vesting. During the year ended December 31, 2025 and 2024, there were no shares that vested as a result of performance milestone achievements. No share-based compensation expense related to these performance-based options was recognized during the years ended December 31, 2025, and 2024, respectively.

Restricted Stock Awards

No RSA was granted during the year ended December 31, 2025. The Company granted 65,000 RSAs during the year ended December 31, 2024. The fair value of all RSAs is based on the market value of the Company’s common stock on the date of grant. Compensation expense, including the effect of estimated forfeitures, is recognized over the applicable service period.

A summary of RSA activity for the years ended December 31, 2025 is as follows:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested as of December 31, 2024		164,174		$	2.56
Granted		—			—
Vested		(60,096	)		2.52
Forfeited		—			—

Unvested as of December 31, 2025		104,078		$	2.57

As of December 31, 2025, the unrecognized share-based compensation expense, net of estimated forfeitures, related to all unvested RSAs held by the Company’s directors is $0.2 million and the weighted average period over which that expense is expected to be recognized is 1.69 years.

Share-based Compensation Plans (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Share-Based Payment Arrangement [Abstract]

Schedule of share-based compensation expense


	Three Months Ended March 31,
	2026		2025
Research and development	$	—	$	12
General and administrative		58		102

	$	58	$	114


	Year Ended December 31,
	2025		2024
Research and development	$	29	$	91
General and administrative		412		534

	$	441	$	625

Schedule of stock option activity

A summary of stock option activity for the three months ended March 31, 2026, is as follows:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Average Intrinsic Value (in thousands)
Outstanding as of December 31, 2025		297,762		$	149.73		4.9	$	—
Granted		—		$	—
Exercised		—		$	—
Cancelled or forfeited		(17,355	)	$	203.65

Outstanding as of March 31, 2026		280,407		$	146.39		4.9	$	—

Exercisable at March 31, 2026		220,760		$	181.20		4.2	$	—

A summary of stock option activity for the year ended December 31, 2025 is as follows:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Average Intrinsic Value (in thousands)
Outstanding as of December 31, 2024		335,448		$	158.98		4.7	$	—
Granted		25,000		$	2.36
Exercised		—		$	—
Cancelled or forfeited		(62,686	)	$	140.44

Outstanding as of December 31, 2025		297,762		$	149.73		4.9	$	—

Exercisable at December 31, 2025		232,385		$	187.20		4.0	$	—

Schedule of weighted-average assumptions used in estimating the fair value of the stock options

The weighted-average Black-Scholes assumptions used in estimating the fair value of the stock options granted by Cyclerion during the years ended December 31, 2025 and 2024 were as follows:


	Year ended December 31,
	2025			2024
Weighted average risk-free interest rate		3.79	%		3.64	%
Expected dividend yield		—			—
Expected option term (in years)		5.4			6.0
Expected stock price volatility		141.07	%		111.97	%

Summary of RSA activity

A summary of RSA activity for the three months ended March 31, 2026 is as follows:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested as of December 31, 2025		104,078		$	2.57
Granted		—			—
Vested		(15,024	)		2.52
Forfeited		—			—

Unvested as of March 31, 2026		89,054		$	2.59

A summary of RSA activity for the years ended December 31, 2025 is as follows:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested as of December 31, 2024		164,174		$	2.56
Granted		—			—
Vested		(60,096	)		2.52
Forfeited		—			—

Unvested as of December 31, 2025		104,078		$	2.57

Loss per share - Schedule Of Earnings Per Share Diluted By Common Class (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Dilutive securities, effect on basic earnings per share, options and restrictive stock units	$ 720,498	$ 829,645	$ 752,877	$ 850,659
Preferred Stock
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Anti-dilutive securities excluded from the calculation of diluted loss per share	351,037	351,037	351,037	351,037
Stock Options
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Dilutive securities, effect on basic earnings per share, options and restrictive stock units	$ 280,407	$ 329,458	$ 297,762	$ 335,448
Restricted Stock Awards
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Dilutive securities, effect on basic earnings per share, options and restrictive stock units	$ 89,054	$ 149,150	$ 104,078	$ 164,174

Share-based Compensation Plans - Schedule of Stock Option Activity (Details) - Employee Stock Option - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Number of Options
Outstanding at beginning of the year (in shares)	297,762	335,448
Granted (in shares)	0	25,000	55,849
Exercised (in shares)	0	0
Cancelled or forfeited (in shares)	(17,355)	(62,686)
Outstanding at end of the year (in shares)	280,407	297,762	335,448
Exercisable (in shares)	220,760	232,385
Weighted Average Exercise Price
Outstanding at beginning of the year (in dollars per share)	$ 149.73	$ 158.98
Granted (in dollars per share)	0	2.36
Exercised (in dollars per share)	0	0
Cancelled or forfeited (in dollars per share)	203.65	140.44
Outstanding as of December 31, 2025	146.39	149.73	$ 158.98
Exercisable (in dollars per share)	$ 181.2	$ 187.2
Weighted Average Remaining Contractual Term (years)
Weighted Average Remaining Contractual Term (Years)	4 years 10 months 24 days	4 years 10 months 24 days	4 years 8 months 12 days
Weighted Average Remaining Contractual Term (Years)	4 years 2 months 12 days	4 years
Aggregate Intrinsic Value, Outstanding	$ 0	$ 0	$ 0
Aggregate Intrinsic Value, Exercisable	$ 0	$ 0

Accrued Expenses and Other Current Liabilities

3 Months Ended

12 Months Ended

Mar. 31, 2026

Dec. 31, 2025

Accrued Liabilities and Other Liabilities [Abstract]

Accrued Expenses and Other Current Liabilities

5. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	March 31, 2026		December 31, 2025
Professional fees	$	984	$	143
Employee compensation		21		13
Other		104		38

Accrued expenses and other current liabilities	$	1,109	$	194

5. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	December 31,		December 31,
	2025		2024
Professional fees	$	143	$	220
Employee compensation		13		33
Other		38		30

Accrued expenses and other current liabilities	$	194	$	283

Nature of Business	3 Months Ended	12 Months Ended
Nature of Business	Mar. 31, 2026	Dec. 31, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	1. Nature of Business Nature of Operations Cyclerion Therapeutics, Inc. (“Cyclerion”, the “Company” or “we”) became an independent public company on April 1, 2019 after Ironwood Pharmaceuticals, Inc. completed a tax-free spin-off of their sGC business. Cyclerion has one employee as of March 31, 2026 and also relies on a team of specialist consultants for its operations. Cyclerion has historically focused on building a pipeline of innovative therapeutics to address serious neuropsychiatric disorders with significant unmet medical need. Prior to the proposed Merger, its strategic focus was centered on the development of a novel therapeutic approach for neuropsychiatric conditions, with the lead indication being treatment-resistant depression (“TRD”), which it believes represents a substantial clinical and commercial opportunity. Over the past year, the Company has refined our strategic direction toward programs that combine established pharmacologic agents with enabling technologies designed to improve precision, reproducibility, and patient outcomes. As part of this strategy, The Company has evaluated multiple opportunities and prioritized CYC-126, an individualized therapy for TRD as its foundational development program. In September 2025, the Company entered into a license agreement with the Massachusetts Institute of Technology (“MIT”) for intellectual property supporting this TRD program. In January 2026, the Company also entered into a collaboration and option-to-license agreement with Medsteer SAS (“Medsteer”), a developer of anesthesia delivery and monitoring technologies. This agreement provides the Company with access to Medsteer’s technical expertise, data assets, and intellectual property relating to technology-enabled drug delivery and physiological monitoring, and grants the Company the right, but not the obligation, to obtain additional rights under specified conditions. The Company intends to evaluate these capabilities as part of our broader development strategy for our TRD program. Given the substantial unmet medical need in TRD, the stage of clinical development, and the potential commercial opportunity, the Company believe this program is well positioned to serve as the foundation of our future development efforts. The program team is currently advancing an integrated clinical, regulatory, and commercial strategy for this TRD program. In parallel with the advancement of our neuropsychiatric strategy, the Company continues to evaluate opportunities related to potentially monetizing its legacy soluble guanylate cyclase (“sGC”) stimulator assets, including potential collaborations, monetization opportunities, or other strategic transactions intended to maximize shareholder value. Praliciguat is an orally administered, once-daily systemic sGC stimulator. On June 3, 2021, Cyclerion entered into a license agreement with Akebia Therapeutics Inc. (“Akebia”) relating to the exclusive worldwide license to Akebia of our rights to the development, manufacture, medical affairs and commercialization of pharmaceutical products containing praliciguat and other related products and forms thereof enumerated in such agreement. In 2021, Akebia paid a $3.0 million upfront payment to the Company upon signing of the license agreement. On December 13, 2024, Cyclerion announced that Cyclerion and Akebia had re-negotiated a mutually beneficial amendment to their exclusive license agreement for praliciguat, a systemic sGC stimulator. Under this new license amendment, Cyclerion received $1.75 million in amendment payments, of which $1.25 million was paid in December 2024 and the remaining additional payment of $0.5 million was received in September 2025. In addition, Akebia is responsible for all intellectual property expenses associated with praliciguat. On December 1, 2025, Akebia publicly announced that it has recently initiated (defined as first patient dosed) Phase 2 clinical trials for the treatment of focal segmental glomerulosclerosis (“FSGS”) using praliciguat. Pursuant to the terms of amendment, upon initiation of a Phase 2 clinical trial in the U.S. for a product, a $1.0 million development milestone payment was received in February 2026. The Company is eligible to receive additional milestone cash payments of up to approximately $557.5 million in total potential future development, regulatory, and commercialization milestone payments for praliciguat. In exchange for a reduction in certain development milestone payments, Cyclerion is eligible to receive certain higher-tiered sales-based royalties ranging from mid-single-digits to twenty percent. Payment of these sums are reserved for Cyclerion stockholders under the “Cyclerion CVR Agreement” described below. Olinciguat is a Phase 2, orally administered, once-daily, vascular sGC stimulator. On July 22, 2024, the Company entered into an Option to License Agreement (the “Option Agreement”) with a third party (the “Optionee”), pursuant to which the Optionee had an option (the “Option”) to enter into an exclusive license to olinciguat for human therapeutics, subject to certain carveouts. Under the terms of the Option Agreement, the Optionee paid the Company an Option fee of $150,000 in August 2024 and subsequent fees totaling $80,000 to extend the term of the Option Agreement. The Optionee originally could exercise the Option on or before March 20, 2025, which was ultimately extended through August 22, 2025. Thereafter, the parties had an additional 60 days to negotiate the terms of a definitive license agreement. The parties were unable to agree upon the terms of a license agreement and the Company provided notice on October 23, 2025 that it was terminating the Option Agreement. The Company is currently exploring potential license opportunities for olinciguat. Zagociguat is a clinical-stage CNS-penetrant sGC stimulator that has shown rapid improvement in cerebral blood flow, functional brain connectivity, brain response to visual stimulus, cognitive performance, and biomarkers associated mitochondrial function and inflammation in clinical studies. CY3018 is a CNS-targeted sGC stimulator that preferentially localizes to the brain and has a pharmacology profile that suggests its potential for the treatment of neuropsychiatric diseases and disorders. On July 28, 2023, the Company sold Zagociguat and CY3018 to Tisento Therapeutics, Inc. (“Tisento”), a newly formed private company focused on their development, in exchange for $8.0 million in cash consideration, $2.4 million as reimbursement for certain operating expenses related to zagociguat and CY3018 for the period between signing and closing of the transaction, and 10% of all of Tisento’s parent’s outstanding equity securities (“Tisento Parent”). 2025 Equity Private Placement On March 21, 2025, the Company entered into a Stock Purchase Agreement (the “2025 Equity Private Placement”) for a private placement of 499,998 shares of the Company’s common stock, at a purchase price of $2.75 per share for total gross proceeds of approximately $1.375 million. The closing of the 2025 Equity Private Placement occurred on March 25, 2025. The Company incurred transaction costs of $0.1 million for the 2025 Equity Private Placement. The Shares issued were not registered under the Securities Act of 1933, as amended, or any state securities laws and will be issued pursuant to the exemption from registration provided for under Section 4(a)(2) of the Securities Act as a transaction not involving a public offering. In connection with the 2025 Equity Private Placement, the Company entered into a Registration Rights Agreement with the investors, dated March 21, 2025, pursuant to which the Company agreed to register the resale of the Shares pursuant to a registration statement which was filed with the SEC and declared effective by the SEC on May 15, 2025. At-the-Market Offering On February 4, 2025, the Company filed a Registration Statement on Form S-3 (the “Shelf”) with the Securities and Exchange Commission (the “SEC”) in relation to the registration of common stock, preferred stock, warrants and units of any combination thereof for an aggregate initial offering price not to exceed $25.0 million. The Registration Statement was declared effective by the SEC in February 2025. On May 7, 2025, the Company and Guggenheim Securities, LLC (“Guggenheim Securities”) entered into a Sales Agreement (the “Sales Agreement”), pursuant to which the Company may offer and sell shares of common stock, no par value per share (the “Shares”), having an aggregate offering price of up to $20,000,000 from time to time through or to Guggenheim Securities, acting as the Company’s agent, subject to the application of General Instruction I.B.6 of Form S-3 (“Instruction I.B.6”) pertaining to primary offerings by certain registrants, including the Company. The Company has provided Guggenheim Securities with customary indemnification rights, and the Company will pay Guggenheim Securities cash commission of 3.0% of the gross proceeds of the Shares sold under the Sales Agreement. During the year ended December 31, 2025, the Company sold 715,220 shares of its common stock for net proceeds of $2.1 million under the Sales Agreement, after deducting commissions paid to Guggenheim Securities of $0.1 million. During the three months ended March 31, 2026, the Company sold 405,000 shares of common stock under the Sales Agreement for net proceeds of approximately $0.8 million. The Company exhausted all sales under the 2025 Shelf. The Merger Agreement On April 1, 2026, Cyclerion entered into a Plan of Merger and Reorganization (as amended, the “Merger Agreement”) with Korsana, a privately held biotechnology company discovering and developing novel therapies to reduce the burden of neurodegenerative diseases, pursuant to which among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Cariboos Merger Sub Corp., a Delaware corporation (“First Merger Sub”), will merge with and into Korsana, with Korsana continuing as a wholly owned subsidiary of Cyclerion and the surviving corporation of the merger (the “First Merger”), and Korsana will merge with and into Cariboos Merger Sub II, LLC, a Delaware limited liability company (“Second Merger Sub” and together with First Merger Sub, “Merger Subs”), with Second Merger Sub being the surviving entity of the merger (the “Second Merger” and, together with the First Merger, the “Merger”). After the completion of the Merger, Second Merger Sub will change its corporate name to “Korsana Biosciences Operating Company, LLC” and Cyclerion will change its name to “Korsana Biosciences, Inc.”. Cyclerion anticipates that the Merger will close in the third quarter of 2026, subject to certain closing conditions, along with the concurrent Korsana Pre-Closing Financing described below. Following the Merger, the current business of Korsana will become the primary business of Cyclerion. At the closing of the First Merger (the “First Effective Time”, and the date on which the closing of the Merger occurs, the “Closing Date”), upon the terms and subject to the conditions set forth in the Merger Agreement: (i) each then-outstanding share of common stock, $0.0001 par value per share, of Korsana (the “Korsana Common Stock”) and Series A Preferred Stock, $0.0001 par value per share of Korsana (“Korsana Series A Preferred Stock”) (including shares of Korsana Common Stock issued in the Korsana Pre-Closing Financing described below), excluding any shares to be cancelled pursuant to the Merger Agreement and excluding dissenting shares, will be automatically converted solely into the right to receive a number of shares of Cyclerion common stock, no par value per share (the “Cyclerion Common Stock”), equal to the exchange ratio as described in the Merger Agreement (the “Exchange Ratio”); provided, that in the event the aggregate number of shares of Cyclerion Common Stock issuable to a holder of Korsana capital stock (when aggregated with all of the shares of the Cyclerion Common Stock outstanding then beneficially owned by such person and its affiliates (as calculated pursuant to Section 13(d) of the Securities Exchange Act of 1934, as amended, and Rule 13d-3 promulgated thereunder) immediately after giving effect to the issuance of the merger consideration) would result in the issuance of shares of Cyclerion Common Stock to a holder in excess of a specified percentage (initially set at a percentage up to 9.99%) of the total outstanding shares of Cyclerion Common Stock (such specified percentage, a “Beneficial Ownership Limitation”), then Cyclerion will issue to any such holder (x) shares of Cyclerion Common Stock up to such holder’s Beneficial Ownership Limitation and (y) in lieu of any shares in excess of such holder’s Beneficial Ownership Limitation, pre-funded warrants (“Cyclerion Pre-Funded Warrants”) to purchase a number of shares of Cyclerion Common Stock upon exercise of such Cyclerion Pre-Funded Warrants equal to such excess shares; (ii) each then-outstanding share of Korsana Series Seed Preferred Stock, $0.0001 par value per share (“Korsana Series Seed Preferred Stock” and, together with the Korsana Series A Preferred Stock, the “Korsana Preferred Stock”), excluding any shares of Korsana Series Seed Preferred Stock to be cancelled pursuant to the Merger Agreement and any dissenting shares, will be converted into the right to receive a number of shares of Cyclerion Series B non-voting convertible preferred stock, no par value per share (“Cyclerion Series B Preferred Stock”), equal to the Exchange Ratio divided by 1,000; (iii) each then-outstanding option (a “Korsana Option”) to purchase shares of Korsana Common Stock will be converted into and become an option to purchase shares of Cyclerion Common Stock on the existing terms and conditions (including with respect to vesting and accelerated vesting), subject to adjustment as set forth in the Merger Agreement; (iv) each then-outstanding restricted stock unit for shares of Korsana Common Stock will be converted into and become a restricted stock unit for shares of Cyclerion Common Stock on the existing terms and conditions (including with respect to vesting and accelerated vesting), subject to adjustment as set forth in the Merger Agreement; and (v) each then-outstanding warrant to purchase shares of Korsana Common Stock will be converted into a warrant to purchase shares of Cyclerion Common Stock on the existing terms and conditions, subject to adjustment as set forth in the Merger Agreement. Each share of Cyclerion Common Stock and Cyclerion Series A Preferred Stock that is issued and outstanding at the First Effective Time will remain issued and outstanding and such shares, subject to the proposed reverse stock split, will be unaffected by the Merger. Prior to the First Effective Time, the Cyclerion board of directors will accelerate the vesting of all options to purchase shares of Cyclerion Common Stock (“Cyclerion Options”) and all restricted stock awards (“Cyclerion RSAs”). Each outstanding Cyclerion Option with an exercise price per share equal to or less than the volume weighted average closing trading price of a share of Cyclerion Common Stock on The Nasdaq Stock Market LLC (“Nasdaq”) for the five consecutive trading days ending three trading days prior to the Calculation Date (as defined in the Merger Agreement), as reported by Bloomberg L.P. (the “Cyclerion Closing Price”), will be cancelled at the First Effective Time and such holder thereof will receive an amount in cash, without interest, less any applicable tax withholding, equal to the product obtained by multiplying the excess of the Cyclerion Closing Price over the exercise price per share of the Cyclerion Common Stock underlying such Cyclerion Option by the number of shares of the Cyclerion Common Stock underlying such Cyclerion Option. Each Cyclerion Option with an exercise price greater than the Cyclerion Closing Price will be cancelled for no consideration. The vesting of each Cyclerion RSA will be accelerated in full. Based on Cyclerion’s capitalization as of December 31, 2025 and Korsana’s capitalization as of March 31, 2026 and assuming Cyclerion’s net cash as of closing being equal to $0, each share of Korsana Common Stock and Korsana Series A Preferred Stock is currently estimated to be entitled to receive approximately 1.1009 shares of Cyclerion Common Stock. Each share of Korsana Series Seed Preferred Stock will be converted into the right to receive a number of shares of Cyclerion Series B Preferred Stock, equal to the Exchange Ratio divided by 1,000. The estimated Exchange Ratio does not give effect to the proposed Cyclerion reverse stock split and is subject to adjustment based on Cyclerion’s estimated net cash at the closing of the First Merger. In connection with the Merger, on April 1, 2026, Korsana entered into a securities purchase agreement (the “Securities Purchase Agreement”) with certain institutional and accredited investors for the purchase of shares of Korsana Common Stock and Pre-Funded Warrants to purchase shares of Korsana Common Stock (the “Korsana Pre-Funded Warrants”) for an aggregate purchase price of approximately $380.0 million, immediately prior to the closing of the Merger (referred to herein as the “Korsana Pre-Closing Financing”). The shares of Korsana Common Stock and Korsana Pre-Funded Warrants that are issued in the Korsana Pre-Closing Financing will be converted into the right to receive a number of shares of Cyclerion Common Stock and Cyclerion Pre-Funded Warrants, respectively, equal to the Exchange Ratio. Korsana and the investors participating in the Korsana Pre-Closing Financing have also agreed to enter into a registration rights agreement at the closing of the Korsana Pre-Closing Financing, pursuant to which, among other things, the Combined Company will agree to provide for the registration and resale of certain shares of Korsana Common Stock that are held by the investors participating in the Korsana Pre-Closing Financing from time to time pursuant to Rule 415 under the Securities Act. Based on its current operating plan, Cyclerion expects that its current cash and cash equivalents will fund its operations until the closing of the contemplated Merger, which is subject to approval by its shareholders and the shareholders of Korsana and other customary closing conditions; however, Cyclerion has based this estimate on assumptions that may prove to be wrong, and Cyclerion could use its capital resources sooner than Cyclerion expects. Cyclerion CVR Agreement At or prior to the first merger, Cyclerion will enter into a Contingent Value Rights Agreement (the “CVR Agreement”) with a designated rights agent (the “Rights Agent”), pursuant to which Cyclerion’s pre-merger shareholders will receive one CVR for each outstanding share of Cyclerion Common Stock and Cyclerion Series A Preferred Stock held by such shareholder on such date. Each CVR will represent the contractual right to receive certain net proceeds, if any, derived from any consideration that is paid to Cyclerion as a result of the disposition of Cyclerion’s pre-Merger legacy assets, net of any indemnity obligations, transaction costs and certain other expenses, during the period beginning on the date of the closing of the merger and ending (i) with respect to the sale, transfer, license or other disposition of all pre-merger legacy assets other than those pre-merger legacy assets described in the following clauses (ii) and (iii), upon the second (2nd) anniversary of the Closing Date, (ii) with respect to Cyclerion’s right to receive payments under the Akebia License Agreement, the earlier of (A) the fifteenth (15th) anniversary of the date of entry into the CVR Agreement and (B) the expiration or earlier termination by Akebia Therapeutics, Inc. of the Akebia License Agreement pursuant to its terms, and (iii) with respect to the sale, transfer or other disposition of the equity interests of Tisento that were acquired by Cyclerion pursuant to that certain Asset Purchase Agreement, dated May 13, 2023, by and among Cyclerion, Tisento and JW Cycle, Inc., the earliest of (A) nine (9) months following the date of the consummation of Tisento’s initial public offering pursuant to a registration statement filed with, and declared effective by, the Securities and Exchange Commission pursuant to the Securities Act, (B) the sale of Tisento, and (C) the seventh (7th) anniversary of the Closing Date. The contingent payments under the CVR Agreement, if they become payable, will become payable to the Rights Agent for subsequent distribution to the holders of the CVRs. In the event that no such proceeds are received, holders of the CVRs will not receive any payment pursuant to the CVR Agreement. There can be no assurance that any holders of CVRs will receive any payments with respect thereto. Basis of Presentation The condensed consolidated financial statements and the related disclosures are unaudited and have been prepared in accordance with accounting principles generally accepted in the U.S. Additionally, certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2025, which was filed with the SEC on March 30, 2026. In the opinion of management, the unaudited interim condensed consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the interim periods presented. The results of operations for the three months ended March 31, 2026 and 2025 are not necessarily indicative of the results that may be expected for the full year or any other subsequent interim period. The condensed consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries, Cyclerion Securities Corporation, Cyclerion Australia Pty Ltd., Cariboos Merger Sub Corp. and Cariboos Merger Sub II, LLC. All significant intercompany accounts and transactions have been eliminated in the preparation of the accompanying condensed consolidated financial statements. Going Concern At each reporting period, in accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern, the Company evaluates whether there are conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs and comparing those needs to the current cash and cash equivalent balances. The Company is required to make certain additional disclosures if it concludes substantial doubt exists and it is not alleviated by the Company’s plans or when its plans alleviate substantial doubt about the Company’s ability to continue as a going concern. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these condensed consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future partnerships, license payments, equity or debt issuances, certain cost reduction measures and the achievement of potential milestone payments from Akebia cannot be considered probable at this time because these plans are not entirely within the Company’s control and/or have not been approved by the Board of Directors as of the date of these condensed consolidated financial statements. The Company expects that its cash and cash equivalents as of March 31, 2026, will be sufficient to fund operations into the third quarter of 2026, however the Company will need to obtain additional funding to sustain operations as it expects to continue to generate operating losses for the foreseeable future. The Company’s expectation to generate negative operating cash flows in the future and the need for additional funding to support its planned operations, raise substantial doubt regarding the Company’s ability to continue as a going concern. Management’s plans to alleviate the conditions that raise substantial doubt include reduced spending, and the pursuit of additional capital. Management has concluded the likelihood that its plan to successfully obtain sufficient funding, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above. The Company’s future operations are highly dependent on the success of the Merger and there can be no assurances that the Merger will be successfully consummated. If the Merger is not consummated, the Company believes that its cash and cash equivalents as of March 31, 2026 would be adequate to fund its operating expenses into the third quarter of 2026. However, in order to continue development of its programs, the Company would need to secure substantial additional funding in the future, from one or more equity or debt financings, collaborations, or other sources. Additional funding may not be available to the Company on acceptable terms, or at all. The Company’s Board of Directors may also decide to pursue a dissolution and liquidation in lieu of continuing program development in the event the Merger is not consummated.	1. Nature of Business Nature of Operations Cyclerion Therapeutics, Inc. (“Cyclerion”, the “Company” or “we”) became an independent public company on April 1, 2019 after Ironwood Pharmaceuticals, Inc. completed a tax-free spin-off of their sGC business. Cyclerion has one employee as of December 31, 2025 and also relies on a team of specialist consultants for its operations. Cyclerion is focused on building a new pipeline of innovative therapeutics to address serious neuropsychiatric diseases. The Company’s current strategic focus is centered on the development of a novel therapeutic approach for treatment-resistant depression (“TRD”), which represents a substantial clinical and commercial opportunity. Over the past year, the Company has refined its strategic direction toward programs that combine established pharmacologic agents with enabling technologies designed to improve precision, reproducibility, and patient outcomes. As part of this strategy, Cyclerion has evaluated multiple opportunities and prioritized CYC-126, an individualized therapy for TRD as its foundational development program. In September 2025, the Company entered into a license agreement with the Massachusetts Institute of Technology (“MIT”) for intellectual property supporting this program (see Note 11), and in January 2026 entered into a collaboration and option-to-license agreement with Medsteer SAS (“Medsteer”) to access certain technology, data assets, and technical know-how related to drug delivery and physiological monitoring. The Company is advancing development planning, regulatory strategy, and commercial positioning for this program and intends to initiate a Phase 2 proof-of-concept study in Australia in the second half of 2026. In parallel with the advancement of its neuropsychiatric strategy, Cyclerion continues to evaluate opportunities related to its legacy soluble guanylate cyclase (“sGC”) stimulator assets, including potential collaborations, monetization opportunities, or other strategic transactions designed to maximize shareholder value. Praliciguat is an orally administered, once-daily systemic sGC stimulator. On June 3, 2021, Cyclerion entered into a license agreement with Akebia Therapeutics Inc. (“Akebia”) relating to the exclusive worldwide license to Akebia of our rights to the development, manufacture, medical affairs and commercialization of pharmaceutical products containing praliciguat and other related products and forms thereof enumerated in such agreement. In 2021, Akebia paid a $3.0 million upfront payment to the Company upon signing of the license agreement. On December 13, 2024, Cyclerion announced that Cyclerion and Akebia have re-negotiated a mutually beneficial amendment to their exclusive license agreement for praliciguat, a systemic sGC stimulator. Under this new license amendment, Cyclerion will receive $1.75 million in amendment payments, of which $1.25 million was paid in December 2024 and an additional payment of $0.5 million was received in September 2025. In addition, Akebia is responsible for all intellectual property expenses associated with praliciguat. On December 1, 2025, Akebia publicly announced that it has recently initiated (defined as first patient dosed) Phase 2 clinical trials for the treatment of focal segmental glomerulosclerosis (“FSGS”) using praliciguat. Pursuant to the terms of amendment, upon initiation of a Phase 2 clinical trial in the U.S. for a product, a $1.0 million development milestone payment would be due to us and it was received in February 2026. The Company is eligible to receive additional milestone cash payments of up to approximately $557.5 million in total potential future development, regulatory, and commercialization milestone payments for praliciguat. In exchange for a reduction in certain development milestone payments, Cyclerion is eligible to receive certain higher-tiered sales-based royalties ranging from mid-single-digits to twenty percent. Olinciguat is a Phase 2, orally administered, once-daily, vascular sGC stimulator. On July 22, 2024, the Company entered into an Option to License Agreement (the “Option Agreement”) with a third party (the “Optionee”), pursuant to which the Optionee had an option (the “Option”) to enter into an exclusive license to olinciguat for human therapeutics, subject to certain carveouts. Under the terms of the Option Agreement, the Optionee paid the Company an Option fee of $150,000 in August 2024 and subsequent fees totaling $80,000 to extend the term of the Option Agreement. The Optionee originally could exercise the Option on or before March 20, 2025, which was ultimately extended through August 22, 2025. Thereafter, the parties had an additional 60 days to negotiate the terms of a definitive license agreement. The parties were unable to agree upon the terms of a license agreement and the Company provided notice on October 23, 2025 that it was terminating the Option Agreement. The Company is currently exploring potential license opportunities for olinciguat. Zagociguat is a clinical-stage CNS-penetrant sGC stimulator that has shown rapid improvement in cerebral blood flow, functional brain connectivity, brain response to visual stimulus, cognitive performance, and biomarkers associated mitochondrial function and inflammation in clinical studies. CY3018 is a CNS-targeted sGC stimulator that preferentially localizes to the brain and has a pharmacology profile that suggests its potential for the treatment of neuropsychiatric diseases and disorders. On July 28, 2023, the Company sold z agociguat and CY3018 to Tisento Therapeutics, Inc. (“Tisento”), a newly formed private company focused on their development, in exchange for $8.0 million in cash consideration, $2.4 million as reimbursement for certain operating expenses related to zagociguat and CY3018 for the period between signing and closing of the transaction, and 10% of all of Tisento’s parent’s outstanding equity securities (“Tisento Parent”). Cyclerion GmbH, a wholly owned subsidiary, was incorporated in Zug, Switzerland on May 3, 2019. The functional currency is the Swiss franc. Cyclerion GmbH was liquidated and de-registered in May 2024. Cyclerion Securities Corporation, a wholly owned subsidiary, was incorporated in Massachusetts on November 15, 2019 and was granted securities corporation status in Massachusetts. Stock Purchase Agreement In March 2023, the Company entered into a stock purchase agreement with the Company’s former Chief Executive Officer (the “CEO”) pursuant to which he invested $5 million in cash for 225,000 shares of common stock and 351,037 shares of Series A Convertible Preferred Stock of the Company at a price of $8.68 per share (after giving effect to the 1-for-20 reverse stock split the Company implemented on May 15, 2023). The Series A Convertible Preferred Stock is convertible into shares of the Company’s common stock on a one-to-one basis. The closing of the equity investment took place on May 19, 2023, and (to comply with Nasdaq listing requirements) the Company’s shareholders approved such convertibility on July 19, 2023. 2025 Equity Private Placement On March 21, 2025, the Company entered into a Stock Purchase Agreement (the “2025 Equity Private Placement”) for a private placement of 499,998 shares of the Company’s common stock, at a purchase price of $2.75 per share for total gross proceeds of approximately $1.375 million. The closing of the 2025 Equity Private Placement occurred on March 25, 2025. The Company incurred transaction costs of $0.1 million for the 2025 Equity Private Placement. The Shares issued were not registered under the Securities Act of 1933, as amended, or any state securities laws and will be issued pursuant to the exemption from registration provided for under Section 4(a)(2) of the Securities Act as a transaction not involving a public offering. In connection with the 2025 Equity Private Placement, the Company entered into a Registration Rights Agreement with the investors, dated March 21, 2025, pursuant to which the Company agreed to register the resale of the Shares pursuant to a registration statement which was filed with the SEC and declared effective by the SEC on May 15, 2025. At-the-Market Offering On February 4, 2025, the Company filed a Registration Statement on Form S-3 (the “Shelf”) with the Securities and Exchange Commission (the “SEC”) in relation to the registration of common stock, preferred stock, warrants and units of any combination thereof for an aggregate initial offering price not to exceed $25.0 million. The Registration Statement was declared effective by the SEC in February 2025. On May 7, 2025, the Company and Guggenheim Securities, LLC (“Guggenheim Securities”) entered into a Sales Agreement (the “Sales Agreement”), pursuant to which the Company may offer and sell shares of common stock, no par value per share (the “Shares”), having an aggregate offering price of up to $20,000,000 from time to time through or to Guggenheim Securities, acting as the Company’s agent, subject to the application of General Instruction I.B.6 of Form S-3 (“Instruction I.B.6”) pertaining to primary offerings by certain registrants, including the Company. The Company has provided Guggenheim Securities with customary indemnification rights, and the Company will pay Guggenheim Securities cash commission of 3.0% of the gross proceeds of the Shares sold under the Sales Agreement. During the year ended December 31, 2025, the Company sold 715,220 shares of its common stock for net proceeds of $2.1 million under the Sales Agreement, after deducting commissions paid to Guggenheim Securities of $0.1 million. Basis of Presentation The consolidated financial statements and the related disclosures have been prepared in accordance with U.S. generally accepted accounting principles. In the opinion of management, the consolidated financial statements reflect all normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and the results of its operations for the fiscal years presented. The consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries, Cyclerion Securities Corporation and Cyclerion GmbH which was dissolved in May 2024. All significant intercompany accounts and transactions have been eliminated in the preparation of the accompanying consolidated financial statements. Going Concern At each reporting period, in accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern, the Company evaluates whether there are conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs and comparing those needs to the current cash and cash equivalent balances. The Company is required to make certain additional disclosures if it concludes substantial doubt exists and it is not alleviated by the Company’s plans or when its plans alleviate substantial doubt about the Company’s ability to continue as a going concern. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future partnerships, equity or debt issuances, certain cost reduction measures and the potential milestones from the Akebia agreement cannot be considered probable at this time because these plans are not entirely within the Company’s control and/or have not been approved by the Board of Directors as of the date of these consolidated financial statements. The Company expects that its cash and cash equivalents as of December 31, 2025, will be sufficient to fund operations through mid-2026, however the Company will need to obtain additional funding to sustain operations as it expects to continue to generate operating losses for the foreseeable future. The Company’s expectation to generate negative operating cash flows in the future and the need for additional funding to support its planned operations, raise substantial doubt regarding the Company’s ability to continue as a going concern. Management’s plans to alleviate the conditions that raise substantial doubt include reduced spending, and the pursuit of additional capital. Management has concluded the likelihood that its plan to successfully obtain sufficient funding, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (3,177)	$ (1,429)	$ (3,528)	$ (3,057)
Adjustments to reconcile net loss to net cash used in operating activities:
Gain from settlement of account payable			0	(363)
Share-based compensation expense	58	114	441	625
Changes in operating assets and liabilities:
Accounts receivable	1,000	(25)	(444)	(556)
Prepaid expenses	129	165	37	21
Other current assets	0	(5)	5	(5)
Accounts payable	(51)	93	118	(445)
Accrued research and development costs	(50)	(2)	146	(38)
Accrued expenses and other current liabilities	915	121	(89)	(515)
Net cash used in operating activities	(1,176)	(968)	(3,314)	(4,333)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(66)	0
Net cash used in investing activities	(66)	0
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from ATM	825	0	2,077	0
Proceeds from private placement	0	1,375	1,375	0
Issuance costs paid for private placement			(130)	0
Net cash provided by financing activities	825	1,375	3,322	0
Effect of exchange rate changes on cash and cash equivalents			0	(6)
Net increase (decrease) in cash and cash equivalents	(417)	407	8	(4,339)
Cash and cash equivalents, beginning of period	3,240	3,232	3,232	7,571
Cash and cash equivalents, end of period	$ 2,823	$ 3,639	$ 3,240	$ 3,232

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Preferred stock, par value (in dollars per share)	$ 0	$ 0	$ 0
Preferred stock, shares authorized	100,000,000	100,000,000	100,000,000
Common stock, par value (in dollars per share)	$ 0	$ 0	$ 0
Common stock, shares authorized	400,000,000	400,000,000	400,000,000
Common stock, shares issued	4,330,314	3,925,314	2,710,096
Common stock, shares outstanding	4,241,260	3,821,236	2,545,922
Series A Convertible Preferred Stock [Member]
Preferred stock, shares issued	351,037	351,037	351,037
Preferred stock, shared outstanding	351,037	351,037	351,037

Fair Value of Financial Instruments (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025	Dec. 31, 2024
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 2,610	$ 3,072	$ 3,025
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	2,610	3,072	3,025
Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	2,610	3,072	3,025
Money market funds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 2,610	$ 3,072	$ 3,025

Summary of Significant Accounting Policies - Revenue, Patent Costs, and Interest and Other Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Interest and other income, net
Finite Lived Intangible Assets [Line Items]
Interest income generated from cash and cash equivalents balances	$ 0.1	$ 0.2
Patents
Finite Lived Intangible Assets [Line Items]
Legal and other fees	$ 0.3	$ 0.6

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Subsequent Events	3 Months Ended	12 Months Ended
Subsequent Events	Mar. 31, 2026	Dec. 31, 2025
Subsequent Events [Abstract]
Subsequent Events	10. Subsequent Events As described above, on April 1, 2026, the Company entered into the Merger Agreement (which was subsequently amended on April 17, 2026) with Korsana, a privately held biotechnology company discovering and developing novel therapies to reduce the burden of neurodegenerative diseases, pursuant to which Korsana will become a wholly owned subsidiary of the Company and the Company will operate under the name Korsana Biosciences, Inc. following the merger. The Company anticipates that the merger will close in the third quarter of 2026, subject to certain closing conditions, along with the concurrent Korsana pre-closing financing. Following the merger, the current business of Korsana will become the primary business of the Company.	12. Subsequent Events On January 6, 2026, the Company sold 405,000 shares of common stock under the Sales Agreement for net proceeds of approximately $0.8 million. The Company exhausted all sales under the 2025 Shelf. On January 3, 2026, the Company and the Medsteer, SAS (“Medsteer”) entered into a Collaboration and Option Agreement (the “Collaboration Agreement”) pursuant to which Medsteer granted to the Company (i) a non-exclusive, worldwide, royalty-free, sublicensable license of certain of Medsteer’s technology, software and intellectual property to develop an anesthetic delivery system with Medsteer and (ii) an exclusive option (the “Option”), exercisable at the Company’s sole discretion, to obtain an exclusive, worldwide, royalty-bearing, sublicensable license of certain of Medsteer’s technology, software and intellectual property to develop or commercialize licensed products in any field of use except for sedation regulation for patients undergoing major surgery, in multi-bed or intensive unit wards, or in the context of medical transport. The Company may exercise the Option at any time until the earlier of the second anniversary of the effective date of the Collaboration Agreement, which period may be extended for an addition two years at the Company’s option and upon payment of a nominal fee or by mutual agreement of the Company and Medsteer. Under the terms of the Collaboration Agreement, the Company will pay to Medsteer a nominal upfront payment, a payment upon exercise of the Option, and Medsteer will be eligible to receive up to $3.7 million upon the achievement of certain development, regulatory and sales milestone payments. Medsteer will also receive an annual royalty payment and royalties in a percentage in the low single digits based on future net sales of licensed products, subject to certain adjustments as set forth in the Collaboration Agreement.

Summary of Significant Accounting Policies - Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Accounting Policies [Abstract]
Income tax, penalties and interest accrued	$ 0	$ 0

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock	Paid-in capital	Accumulated deflicit	Accumulated other comprehensive loss
Beginning balance at Dec. 31, 2023	$ 11,288			$ 275,717	$ (264,417)	$ (12)
Beginning balance (in shares) at Dec. 31, 2023		2,474,159	351,037
Net loss	(3,057)				(3,057)
Vesting of restricted stock awards (in shares)		71,763
Share-based compensation expense related to issuance of stock options and restricted stock awards	625			625
Foreign currency translation adjustment	(6)					(6)
Release of foreign currency translation adjustment upon liquidation of a subsidiary					(18)	$ 18
Ending balance at Dec. 31, 2024	$ 8,850			276,342	(267,492)
Ending balance (in shares) at Dec. 31, 2024	2,545,922	2,545,922	351,037
Issuance of common stock - private placement, net of issuance cost (in share)		499,998
Issuance of common stock - private placement, net of issuance cost	$ 1,245			1,245
Net loss	(1,429)				(1,429)
Vesting of restricted stock awards (in shares)		15,024
Share-based compensation expense related to issuance of stock options and restricted stock awards	114			114
Ending balance at Mar. 31, 2025	8,780			277,701	(268,921)
Ending balance (in shares) at Mar. 31, 2025		3,060,944	351,037
Beginning balance at Dec. 31, 2024	$ 8,850			276,342	(267,492)
Beginning balance (in shares) at Dec. 31, 2024	2,545,922	2,545,922	351,037
Issuance of common stock - private placement, net of issuance cost (in share)		499,998
Issuance of common stock - private placement, net of issuance cost	$ 1,245			1,245
Issuance of common stock - ATM (in shares)		715,220
Issuance of common stock - ATM	2,077			2,077
Net loss	(3,528)				(3,528)
Vesting of restricted stock awards (in shares)		60,096
Share-based compensation expense related to issuance of stock options and restricted stock awards	441			441
Foreign currency translation adjustment	0
Ending balance at Dec. 31, 2025	$ 9,085			280,105	(271,020)
Ending balance (in shares) at Dec. 31, 2025	3,821,236	3,821,236	351,037
Issuance of common stock - ATM (in shares)		405,000
Issuance of common stock - ATM	$ 825			825
Net loss	(3,177)				(3,177)
Vesting of restricted stock awards (in shares)		15,024
Share-based compensation expense related to issuance of stock options and restricted stock awards	58			58
Ending balance at Mar. 31, 2026	$ 6,791			$ 280,988	$ (274,197)
Ending balance (in shares) at Mar. 31, 2026	4,241,260	4,241,260	351,037

Share-based Compensation Plans - Schedule of Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 58	$ 114	$ 441	$ 625
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	0	12	29	91
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 58	$ 102	$ 412	$ 534

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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