Summary of Significant Accounting Policies (Policies) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2025 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Accounting Policies [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Basis of Presentation | The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) as found in the Accounting Standards Codification (“ASC”) of the Financial Accounting Standards Board (“FASB”). | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Consolidation | The accompanying consolidated financial statements include the accounts of Sionna Therapeutics, Inc., and its wholly owned subsidiary, Sionna Therapeutics Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Use of Estimates | The preparation of consolidated financial statements in conformity with GAAP requires management to make judgments, assumptions, and estimates that affect the reported amounts of assets, liabilities and expenses and the related disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected within the consolidated financial statements include, but are not limited to, research and development expenses and accruals and the valuation of the Company’s common shares in connection with the accounting for stock-based awards. The Company bases its estimates on historical experience and various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances and facts. Changes in estimates are recorded in the period in which they become known. Actual results may differ from those estimates or assumptions. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cash, Cash Equivalents and Restricted Cash | The Company considers all highly liquid investments with original maturities of ninety days or less at the time of purchase to be cash equivalents. Cash and cash equivalents typically include cash held in deposit accounts and money market funds. Cash accounts with any type of restriction are classified as restricted cash.
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| Marketable Securities | The Company classifies marketable securities with a remaining maturity greater than three months at the time of purchase and less than one year from the balance sheet date as current. Marketable securities are classified as long-term assets on the consolidated balance sheets if the maturity exceeds one year, and the Company does not intend to utilize the marketable securities to fund current operations. The Company classifies all of its investments as available-for-sale securities. Accordingly, these investments are recorded at fair value. Realized gains and losses and amortization of discounts and premiums are included in interest income, which is a component of other income. Unrealized gains and losses on available-for-sale securities are included in accumulated other comprehensive gain as a component of stockholders’ equity (deficit) until realized. Interest receivables earned on marketable securities are recorded as a component of prepaid expenses and other current assets. At each balance sheet date, the Company assesses available-for-sale debt securities in an unrealized loss position to determine whether the unrealized loss or any potential credit losses should be recognized. The Company evaluates whether it intends to sell, or it is more likely than not that it will be required to sell the security before recovery of its amortized cost basis. The Company also evaluates whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, the Company considers the severity of the impairment, any changes in interest rates, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in other income. There have been no impairment or credit losses recognized during any of the periods presented.
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| Concentration of Credit Risk | Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash, cash equivalents and marketable securities. Periodically, the Company may maintain deposits in financial institutions in excess of government insured limits. The Company believes that it is not exposed to significant credit risk as its deposits are held at financial institutions that management believes to be of high credit quality and the Company has not experienced any losses on these deposits. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Off-Balance Sheet Risk | The Company regularly invests excess cash with major financial institutions in money market funds, U.S. Treasury securities and government agency securities, corporate bonds, and commercial paper, all of which can be readily purchased and sold using established markets. The Company believes that the market risk arising from its holdings of these financial instruments is mitigated based on the fact that many of these securities are either government-backed or of high credit rating. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fair Value of Financial Instruments | Certain assets and liabilities of the Company are carried at fair value under GAAP. 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 market prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3—Unobservable inputs for the asset or liability (i.e., supported by little or no market activity). Level 3 inputs include management’s own assumptions about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk). A financial instrument’s level within the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of the fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. The Company does not currently have recurring fair value measurements classified within Level 3. The carrying values of prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.
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| Property and Equipment, net | Property and equipment is stated at cost net of accumulated depreciation. Costs of major additions and betterments are capitalized. Maintenance and repairs to an asset that do not improve or extend its life are expensed in the period incurred. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows:
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| Impairment of Long-Lived Assets | Long-lived assets consist primarily of property and equipment and right-of-use assets. The Company continually evaluates whether events or circumstances have occurred that indicate that the estimated remaining useful life of its long-lived assets may warrant revision or that the carrying value of these assets may be impaired. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use or disposition of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written down to their fair values. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Leases | At the inception of an arrangement the Company determines whether the arrangement contains a lease. Operating leases are included in operating lease right-of-use lease asset (“ROU asset”), operating lease liability, current, and operating lease liability, noncurrent, on the Company’s consolidated balance sheets. Assets subject to finance leases are included in property and equipment, and the related lease obligation is included in other current liabilities and other long-term liabilities on the Company’s consolidated balance sheets. Lease expense for operating leases is recognized on a straight-line basis over the lease term as an operating expense. As of December 31, 2025 and 2024, the Company did not have any finance leases. The Company has elected the short-term lease recognition exemption for short-term leases, which allows the Company not to recognize lease liabilities and ROU assets on the consolidated balance sheets for leases with an original term of twelve months or less. ROU assets represent the Company’s right to use an underlying asset for the lease term, and lease obligations represent the Company’s obligation to make lease payments arising from the lease. Operating lease liabilities and their corresponding ROU assets are initially recognized based on the present value of lease payments over the expected remaining lease term. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that the Company will exercise the option. Certain adjustments to the ROU asset may be required for items such as incentives received from the lessor. The interest rate implicit in lease contracts is typically not readily determinable. Therefore, the Company utilizes its incremental borrowing rate to discount lease payments. The incremental borrowing rate reflects the fixed rate at which the Company could borrow, on a collateralized basis, the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. Leases generally provide for payments of non-lease components, such as common area maintenance, real estate taxes and other costs associated with the leased property. The Company accounts for non-lease components together with lease components. Variable lease payments, such as periodic adjustments for inflation, reimbursement of real estate taxes, and variable common area maintenance are expensed as incurred as variable lease costs and are not recorded on the consolidated balance sheets. Sublease income is recognized on a straight-line basis over the term of the sublease agreement and is recorded within Other Income on the consolidated statements of operations and comprehensive loss.
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| Research and Development Expenses and Accruals | Research and development costs include (i) employee-related expenses, including salaries, benefits, and stock-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research organizations (“CRO”) agreements, contract development and manufacturing organizations (“CDMOs”), consultants and scientific advisors; (iii) costs associated with preclinical and clinical activities and (iv) lab supplies, lab expenses and an allocation of rent, depreciation, and infrastructure. The Company recognizes research and development costs in the periods in which they are incurred because these activities have no alternative future use. Typically, external expenses are recognized based on an evaluation of the progress to completion of specific tasks using information obtained from (i) internal personnel regarding the services that have been performed on the Company's behalf and estimating the associated cost incurred for those services or (ii) information provided to the Company by their service providers as of each reporting date. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses, which are expensed as the related goods are delivered or the services are performed, or when it is no longer expected that the goods will be delivered, or the services rendered. Significant judgments and estimates are made in determining accrued or prepaid expense balances at the end of any reporting period.
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| Asset Acquisitions and Acquired In-Process Research and Development Expense | The Company accounts for acquisitions of assets or a group of assets that do not meet the definition of a business as asset acquisitions based on the cost to acquire the asset or group of assets, which include certain transaction costs. In an asset acquisition, the cost to acquire is allocated to the identifiable assets acquired and liabilities assumed based on their relative fair values as of the acquisition date. No goodwill is recorded in an asset acquisition. Assets that are acquired in an asset acquisition for use in research and development activities that have an alternative future use are capitalized as in process research and development (“IPR&D”). Acquired IPR&D that has no alternative future use as of the acquisition date is recognized as research and development expense as of the acquisition date. The costs to acquire IPR&D are presented as operating activities in the consolidated statements of cash flows in the period acquired. The Company will recognize additional research and development expenses in the future if and when the Company becomes obligated to make contingent milestone or royalty payments which are governed by the terms of the agreements by which it acquired the IPR&D assets. Developmental and regulatory milestone payments will be recorded when the milestone is achieved, and commercial milestones, such as sales-based milestone payments, and royalties will be recorded when the underlying sale(s) occur.
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| Patent Costs | All patent-related costs incurred in connection with filing and prosecuting patent applications such as direct application fees, and legal and consulting expenses are expensed as incurred due to the uncertainty about the recovery of the expenditure. Patent-related costs are classified as general and administrative expenses within the Company’s consolidated statements of operations and comprehensive loss. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Deferred Offering Costs | The Company capitalizes certain legal, professional accounting and other third-party fees that are direct and incremental costs associated with in-process equity financings as deferred offering costs until such financing is consummated. After consummation of the equity financing, these costs are recorded as a reduction of the proceeds generated as a result of the offering within additional paid-in capital. In the event that the equity financing is abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the condensed consolidated statements of operations and comprehensive loss.
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| Convertible Preferred Stock and Fair Value of Common Stock | Prior to the completion of the Company's IPO, the Company had outstanding convertible preferred stock, which was classified as temporary equity in the consolidated balance sheets. Upon the completion of the IPO, all outstanding shares of convertible preferred stock automatically converted into shares of common stock, and the carrying value of the convertible preferred stock was reclassified to stockholder's equity. As of December 31, 2025, no shares of convertible preferred stock were outstanding. Fair Value of Common Stock Prior to the completion of the Company's IPO, the Company determined the estimated fair value of common stock based on a number of objective and subjective factors, including, but not limited to, external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of convertible preferred stock and the superior rights and preferences of securities senior to the Company’s common stock at the time, and the likelihood and potential timing of achieving a liquidity event, such as an initial public offering, in light of prevailing market conditions. The Company utilized valuation methodologies to estimate the fair value of common stock that were in accordance with the guidance outlined in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation, including the option pricing method and the probability-weighted expected return method. These methodologies required the use of significant management judgment and assumptions. Since completion of the IPO, the fair value of the Company's common stock has been determined based on the closing market price of the Company's common stock on the date of equity grant.
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| Stock-Based Compensation | The Company measures all stock options and other stock-based awards granted to employees, non-employees, and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. The Company’s stock-based payments include stock options and grants of restricted common stock awards. Generally, the Company issues stock-based awards with only service-based vesting conditions. The Company’s policy is to account for forfeitures when they occur. Stock-based compensation expense is classified in the accompanying consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients service payments are classified. Restricted common stock awards are subject to repurchase rights until such awards meet all vesting conditions. Accordingly, the Company recorded the proceeds from the issuance of restricted common stock awards as a liability in the consolidated balance sheets. The restricted common stock liability was reclassified into stockholders’ equity as the restricted common stock vested. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. Due to the lack of Company-specific historical and implied volatility information, the Company estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until it has adequate historical data regarding the volatility of its own traded stock price. The Company uses the simplified method as prescribed by the Securities and Exchange Commission’s Staff Accounting Bulletin No. 107, Share-Based Payment, to estimate the expected term for options granted to employees and non-employees as the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero because the Company has never paid cash dividends on common shares and does not expect to pay any cash dividends in the foreseeable future.
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| Income Taxes | The Company’s provision for income taxes, deferred tax assets and liabilities, and reserves for unrecognized tax benefits reflect management's best assessment of estimated future taxes to be paid. Significant judgments and estimates based on interpretations of existing tax laws or regulations in the United States are required in determining our provision for income taxes. Changes in tax laws, statutory tax rates, and estimates of our future taxable income could impact the deferred tax assets and liabilities provided for in the consolidated financial statements and would require an adjustment to the provision for income taxes. The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, which are considered appropriate as well as the related net interest and penalties.
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| Net Loss Per Share | Basic net loss per share is computed by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. Diluted net loss per share is computed using the weighted-average number of common shares outstanding during the period, and if dilutive, the weighted-average number of potential common shares outstanding. Potentially dilutive securities consist of stock options, restricted stock awards, and other common stock equivalents. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share is the same as basic net loss per share, as the inclusion of potentially dilutive common shares would be antidilutive.
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| Comprehensive Loss | Comprehensive loss includes net loss as well as other changes in stockholder’s equity (deficit) that result from transactions and events other than those with stockholders. The Company’s unrealized gains and losses on marketable securities represent the only component of other comprehensive gain that are excluded from the reported net loss and that are presented in the consolidated statements of operations and comprehensive loss. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Segment Information | The Company is managed as one operating segment, and thus reports as a single reportable segment. This operating segment is focused on the research and development of cystic fibrosis therapies. Management assessed the financial information routinely reviewed by the Company's Chief Operating Decision Maker ("CODM"), its President and Chief Executive Officer, to monitor the Company's operating performance and support decision making regarding allocation of resources to its operations, and determined that performance is continuously monitored at the consolidated level. The measure of segment assets is reported on the consolidated balance sheet as total consolidated assets. The measure used by the CODM in assessing performance and deciding how to allocate resources is based on consolidated net loss, as reported on the consolidated statement of operations and comprehensive loss. The CODM uses consolidated net loss, as reported in the consolidated statement of operations, to assess performance and allocate resources by evaluating operating results against expectations.
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| Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements Not Yet Adopted | In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740: Improvements to Income Tax Disclosures) (“ASU 2023-09”). ASU 2023-09 provides more transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and incomes taxes paid information. For public companies, the amendments were effective for annual periods beginning after December 15, 2024. The Company adopted the amendments retrospectively for the year-ended December 31, 2025. The adoption did not have a material impact on the Company's consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses ("ASU 2024-03"), which requires entities to disclose additional information about specific expense categories in the notes to the financial statements. ASU 2024-03 is effective for annual periods beginning after December 15, 2026 and for interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. ASU 2024-03 may be applied retrospectively or prospectively. The Company is currently evaluating the effect of this update on its consolidated financial statements and related disclosures. In September 2025, the FASB issued ASU 2025-07, Derivatives Scope Refinement, ("ASU 2025-07"). ASU 2025-07 creates a scope exception within ASC 815 for certain contracts with underlyings tied to a party's operations or activities (such as regulatory approval, clinical, or earnings milestones), which may cause some arrangements that previously met the derivative definition to no longer be accounted for as derivatives. The guidance is effective for fiscal years beginning after December 15, 2026, including interim periods. Early adoption is permitted. Entities may adopt prospectively for new or modified contracts after the adoption date, or modified retrospectively for contracts outstanding at adoption with a cumulative-effect adjustment to opening retained earnings. The Company expects to adopt prospectively and does not expect a material impact, though this guidance may affect the accounting for future milestone-linked arrangements executed after adoption
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