Significant Accounting Policies	12 Months Ended
Significant Accounting Policies	Sep. 30, 2025
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Basis of Presentation: The Consolidated Financial Statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") and pursuant to the requirements for reporting on Form 10-K and Regulation S-X. All intercompany balances and transactions have been eliminated. The Company is an investment company following the accounting and reporting guidance in ASC Topic 946, Financial Services - Investment Companies ("ASC 946"). Use of Estimates: The preparation of the financial statements in conformity with GAAP requires management to make certain estimates and assumptions affecting amounts reported in the financial statements and accompanying notes. These estimates are based on the information that is currently available to the Company and on various other assumptions that the Company believes to be reasonable under the circumstances. Changes in the economic and political environments, financial markets and any other parameters used in determining these estimates could cause actual results to differ and such differences could be material. Significant estimates include the valuation of investments and revenue recognition. Consolidation: The accompanying Consolidated Financial Statements include the accounts of Oaktree Specialty Lending Corporation and its consolidated subsidiaries. Each consolidated subsidiary is wholly-owned and, as such, consolidated into the Consolidated Financial Statements. Certain subsidiaries that hold investments are treated as pass through entities for U.S. federal income tax purposes. The assets of certain of the consolidated subsidiaries are not directly available to satisfy the claims of the creditors of Oaktree Specialty Lending Corporation or any of its other subsidiaries. As an investment company, portfolio investments held by the Company are not consolidated into the Consolidated Financial Statements but rather are included on the Statements of Assets and Liabilities as investments at fair value. Fair Value Measurements: Oaktree, as the valuation designee of the Company's Board of Directors pursuant to Rule 2a-5 under the Investment Company Act, determines the fair value of the Company's assets, including unfunded commitments, on at least a quarterly basis in accordance with ASC 820. ASC 820 defines fair value as the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A liability's fair value is defined as the amount that would be paid to transfer the liability to a new obligor, not the amount that would be paid to settle the liability with the creditor. ASC 820 prioritizes the use of observable market prices over entity-specific inputs. Where observable prices or inputs are not available or reliable, valuation techniques are applied. These valuation techniques involve some level of management estimation and judgment, the degree of which is dependent on the price transparency for the investments or market and the investments' complexity. Hierarchical levels, defined by ASC 820 and directly related to the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities, are as follows: •Level 1 — Unadjusted, quoted prices in active markets for identical assets or liabilities as of the measurement date. •Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data at the measurement date for substantially the full term of the assets or liabilities. •Level 3 — Unobservable inputs that reflect Oaktree's best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. If inputs used to measure fair value fall into different levels of the fair value hierarchy, an investment's level is based on the lowest level of input that is significant to the fair value measurement. Oaktree's assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the investment. This includes investment securities that are valued using "bid" and "ask" prices obtained from independent third party pricing services or directly from brokers. These investments may be classified as Level 3 because the quoted prices may be indicative in nature for securities that are in an inactive market, may be for similar securities or may require adjustments for investment-specific factors or restrictions. Financial instruments with readily available quoted prices generally will have a higher degree of market price observability and a lesser degree of judgment inherent in measuring fair value. As such, Oaktree obtains and analyzes readily available market quotations provided by pricing vendors and brokers for all of the Company's investments for which quotations are available. In determining the fair value of a particular investment, pricing vendors and brokers use observable market information, including both binding and non-binding indicative quotations. Oaktree seeks to obtain at least two quotations for the subject or similar securities, typically from pricing vendors. If Oaktree is unable to obtain two quotes from pricing vendors, or if the prices obtained from pricing vendors are not within Oaktree's set threshold, Oaktree seeks to obtain a quote directly from a broker making a market for the asset. Oaktree evaluates the quotations provided by pricing vendors and brokers based on available market information, including trading activity of the subject or similar securities, or by performing a comparable security analysis to ensure that fair values are reasonably estimated. Generally, Oaktree does not adjust any of the prices received from these sources. Oaktree also performs back-testing of valuation information obtained from pricing vendors and brokers against actual prices received in transactions. In addition to ongoing monitoring and back-testing, Oaktree performs due diligence procedures over pricing vendors to understand their methodology and controls to support their use in the valuation process. If the quotations obtained from pricing vendors or brokers are determined to not be reliable or are not readily available, Oaktree values such investments using any of three different valuation techniques. The first valuation technique is the transaction precedent technique, which utilizes recent or expected future transactions of the investment to determine fair value, to the extent applicable. The second valuation technique is an analysis of the enterprise value ("EV") of the portfolio company. EV means the entire value of the portfolio company to a market participant, including the sum of the values of debt and equity securities used to capitalize the enterprise at a point in time. The EV analysis is typically performed to determine (i) the value of equity investments, (ii) whether there is credit impairment for debt investments and (iii) the value for debt investments that the Company is deemed to control under the Investment Company Act. To estimate the EV of a portfolio company, Oaktree analyzes various factors, including the portfolio company’s historical and projected financial results, macroeconomic impacts on the company and competitive dynamics in the company’s industry. Oaktree also utilizes some or all of the following information based on the individual circumstances of the portfolio company: (i) valuations of comparable public companies, (ii) recent sales of private and public comparable companies in similar industries or having similar business or earnings characteristics, (iii) purchase prices as a multiple of their earnings or cash flow, (iv) the portfolio company’s ability to meet its forecasts and its business prospects, (v) a discounted cash flow analysis, (vi) estimated liquidation or collateral value of the portfolio company's assets and (vii) offers from third parties to buy the portfolio company. Oaktree may probability weight potential sale outcomes with respect to a portfolio company when uncertainty exists as of the valuation date. The third valuation technique is a market yield technique, which is typically performed for non-credit impaired debt investments. In the market yield technique, a current price is imputed for the investment based upon an assessment of the expected market yield for a similarly structured investment with a similar level of risk, and Oaktree considers the current contractual interest rate, the capital structure and other terms of the investment relative to risk of the company and the specific investment. A key determinant of risk, among other things, is the leverage through the investment relative to the EV of the portfolio company. As debt investments held by the Company are substantially illiquid with no active transaction market, Oaktree depends on primary market data, including newly funded transactions and industry specific market movements, as well as secondary market data with respect to high yield debt instruments and syndicated loans, as inputs in determining the appropriate market yield, as applicable. In accordance with ASC 820-10, certain investments that qualify as investment companies in accordance with ASC 946 may be valued using net asset value as a practical expedient for fair value. Consistent with FASB guidance under ASC 820, these investments are excluded from the hierarchical levels. These investments are generally not redeemable. Oaktree estimates the fair value of certain privately held warrants using a Black Scholes pricing model, which includes an analysis of various factors and subjective assumptions, including the current stock price (by using an EV analysis as described above), the expected period until exercise, expected volatility of the underlying stock price, expected dividends and the risk free rate. Changes in the subjective input assumptions can materially affect the fair value estimates. Rule 2a-5 under the Investment Company Act permits boards of directors of registered investment companies and Business Development Companies to either (i) choose to determine fair value in good faith or (ii) designate a valuation designee tasked with determining fair value in good faith, subject to the board’s oversight. The Company's Board of Directors has designated Oaktree to serve as its valuation designee. Oaktree undertakes a multi-step valuation process each quarter in connection with determining the fair value of the Company's investments: •The quarterly valuation process begins with each portfolio company or investment being initially valued by Oaktree's valuation team; •Preliminary valuations are then reviewed and discussed with management of Oaktree; •Separately, independent valuation firms prepare valuations of the Company's investments, on a selected basis, for which market quotations are not readily available or are readily available but deemed not reflective of the fair value of the investment, and submit the reports to the Company and provide such reports to Oaktree; •Oaktree compares and contrasts its preliminary valuations to the valuations of the independent valuation firms and prepares a valuation report for the Audit Committee; •The Audit Committee reviews the valuation report with Oaktree, and Oaktree responds and supplements the valuation report to reflect any discussions between Oaktree and the Audit Committee; and •Oaktree, as valuation designee, determines the fair value of each investment in the Company's portfolio. The fair value of the Company's investments as of September 30, 2025 and September 30, 2024 was determined by Oaktree, as the Company's valuation designee. The Company has and will continue to engage independent valuation firms to provide assistance regarding the determination of the fair value of a portion of its portfolio securities for which market quotations are not readily available or are readily available but deemed not reflective of the fair value of the investment each quarter. Due to the inherent uncertainty of determining the fair value of investments that do not have a readily available market value, the fair value of the Company’s investments may fluctuate from period to period. Because of the inherent uncertainty of valuation, these estimated values may differ significantly from the values that would have been reported had a ready market for the investments existed, and it is reasonably possible that the difference could be material. With the exception of the line items entitled "deferred financing costs," "deferred offering costs," "other assets," "credit facilities payable" and "unsecured notes payable," which are reported at amortized cost, all assets and liabilities approximate fair value on the Consolidated Statements of Assets and Liabilities. The carrying value of the line items titled "interest, dividends and fees receivable," "due from portfolio companies," "receivables from unsettled transactions," "due from broker," "accounts payable, accrued expenses and other liabilities," "base management fee and incentive fee payable," "due to affiliate," "interest payable " and "payables from unsettled transactions" approximate fair value due to their short maturities. Foreign Currency Translation: The accounting records of the Company are maintained in U.S. dollars. All assets and liabilities denominated in foreign currencies are translated into U.S. dollars based on the prevailing foreign exchange rate on the reporting date. The Company does not isolate that portion of the results of operations resulting from changes in foreign exchange rates on investments from the fluctuations arising from changes in market prices of securities held. The Company’s investments in foreign securities may involve certain risks, including foreign exchange restrictions, expropriation, taxation or other political, social or economic risks, all of which could affect the market and/or credit risk of the investment. In addition, changes in the relationship of foreign currencies to the U.S. dollar can significantly affect the value of these investments and therefore the earnings of the Company. Derivative Instruments: Foreign Currency Forward Contracts The Company uses foreign currency forward contracts to reduce the Company's exposure to fluctuations in the value of foreign currencies. In a foreign currency forward contract, the Company agrees to receive or deliver a fixed quantity of one currency for another at a pre-determined price at a future date. Foreign currency forward contracts are marked-to-market at the applicable forward rate. Unrealized appreciation (depreciation) on foreign currency forward contracts is recorded within derivative assets or derivative liabilities on the Consolidated Statements of Assets and Liabilities by counterparty on a net basis, not taking into account collateral posted which is recorded separately, if applicable. Purchases and settlements of foreign currency forward contracts having the same settlement date and counterparty are generally settled net and any realized gains or losses are recognized on the settlement date. The Company does not utilize hedge accounting with respect to foreign currency forward contracts and, as such, the Company recognizes its foreign currency forward contracts at fair value with changes included in the net unrealized appreciation (depreciation) on the Consolidated Statements of Operations. Interest Rate Swaps The Company uses interest rate swaps to hedge the Company's fixed rate debt. The Company designated the interest rate swaps as the hedging instruments in an effective hedge accounting relationship, and therefore the periodic payments are recognized as components of interest expense in the Consolidated Statements of Operations. Depending on the nature of the balance at period end, the fair value of each interest rate swap is either included as a derivative asset or derivative liability on the Company's Consolidated Statements of Assets and Liabilities. The change in fair value of the interest rate swaps is offset by a change in the carrying value of the fixed rate debt. Any amounts paid to the counterparty to cover collateral obligations under the terms of the interest rate swap agreements are included in due from broker on the Company's Consolidated Statements of Assets and Liabilities. Restricted Securities: The Company may invest in securities that may be deemed “restricted securities” for purposes of Regulation S-X. Disposal of these restricted securities, which are valued in accordance with the Company’s valuation policy as described under “—Fair Value Measurements”, may involve time-consuming negotiations and additional expense, and prompt sale at an acceptable price may be difficult due to legal and/or contractual restrictions. Information regarding restricted securities is included in the Schedules of Investments. Investment Income: Interest Income Interest income, adjusted for accretion of original issue discount ("OID"), is recorded on an accrual basis to the extent that such amounts are expected to be collected. The Company stops accruing interest on investments when it is determined that interest is no longer collectible. Investments that are expected to pay regularly scheduled interest in cash are generally placed on non-accrual status when there is reasonable doubt that principal or interest cash payments will be collected. Cash interest payments received on investments may be recognized as income or a return of capital depending upon management’s judgment. A non-accrual investment is restored to accrual status if past due principal and interest are paid in cash and the portfolio company, in management’s judgment, is likely to continue timely payment of its remaining obligations. As of September 30, 2025, there were ten investments on non-accrual status that in aggregate represented 6.5% and 3.0% of total debt investments at cost and fair value, respectively. As of September 30, 2024, there were nine investments on non-accrual status that in aggregate represented 4.9% and 4.0% of total debt investments at cost and fair value, respectively. In connection with its investment in a portfolio company, the Company sometimes receives nominal cost equity that is valued as part of the negotiation process with the portfolio company. When the Company receives nominal cost equity, the Company allocates its cost basis in the investment between debt securities and the nominal cost equity at the time of origination. Any resulting discount from recording the loan, or otherwise purchasing a security at a discount, is accreted into interest income over the life of the loan. PIK Interest Income The Company's investments in debt securities may contain PIK interest provisions. PIK interest, which generally represents contractually deferred interest added to the loan balance that is generally due at the end of the loan term, is generally recorded on the accrual basis to the extent such amounts are expected to be collected. The Company generally ceases accruing PIK interest if there is insufficient value to support the accrual or if the Company does not expect the portfolio company to be able to pay all principal and interest due. The Company's decision to cease accruing PIK interest on a loan or debt security involves subjective judgments and determinations based on available information about a particular portfolio company, including whether the portfolio company is current with respect to its payment of principal and interest on its loans and debt securities; financial statements and financial projections for the portfolio company; the Company's assessment of the portfolio company's business development success; information obtained by the Company in connection with periodic formal update interviews with the portfolio company's management and, if appropriate, the private equity sponsor; and information about the general economic and market conditions in which the portfolio company operates. The Company's determination to cease accruing PIK interest is generally made well before the Company's full write-down of a loan or debt security. In addition, if it is subsequently determined that the Company will not be able to collect any previously accrued PIK interest, the fair value of the loans or debt securities would be reduced by the amount of such previously accrued, but uncollectible, PIK interest. The accrual of PIK interest on the Company’s debt investments increases the recorded cost basis of these investments in the Consolidated Financial Statements including for purposes of computing the capital gains incentive fee payable by the Company to Oaktree. To maintain its status as a RIC, certain income from PIK interest may be required to be distributed to the Company’s stockholders, even though the Company has not yet collected the cash and may never do so. Fee Income Oaktree or its affiliates may provide financial advisory services to portfolio companies and, in return, the Company may receive fees for capital structuring services. These fees are generally non-recurring and are recognized by the Company upon the investment closing date. The Company may also receive additional fees in the ordinary course of business, including servicing, amendment, exit and prepayment fees, which are classified as fee income and recognized as they are earned or the services are rendered. Dividend Income The Company generally recognizes dividend income on the ex-dividend date for public securities and the record date for private equity investments. Distributions received from private equity investments are evaluated to determine if the distribution should be recorded as dividend income or a return of capital. Generally, the Company will not record distributions from private equity investments as dividend income unless there are sufficient earnings at the portfolio company prior to the distribution. Distributions that are classified as a return of capital are recorded as a reduction in the cost basis of the investment. Cash and Cash Equivalents and Restricted Cash: Cash and cash equivalents consist of demand deposits and highly liquid investments with maturities of three months or less when acquired. The Company places its cash and cash equivalents and restricted cash with financial institutions and, at times, cash held in bank accounts exceeds the Federal Deposit Insurance Corporation ("FDIC") insurance limit. Cash and cash equivalents are included on the Company's Consolidated Schedule of Investments and cash equivalents are classified as Level 1 assets. As of September 30, 2025, the Company did not have any restricted cash. As of September 30, 2024, included in restricted cash was $14.6 million that was held at Deutsche Bank Trust Company Americas in connection with the OSI2 Citibank Facility (as defined in Note 6. Borrowings). Due from Portfolio Companies: Due from portfolio companies consists of amounts payable to the Company from its portfolio companies, including proceeds from the sale of portfolio companies not yet received or being held in escrow and excluding those amounts attributable to interest, dividends or fees receivable. These amounts are recognized as they become payable to the Company (e.g., principal payments on the scheduled amortization payment date). Receivables/Payables from Unsettled Transactions: Receivables/payables from unsettled transactions consist of amounts receivable to or payable by the Company for transactions that have not settled at the reporting date. Deferred Financing Costs: Deferred financing costs consist of fees and expenses paid in connection with the closing or amending of credit facilities and debt offerings. Deferred financing costs in connection with credit facilities are capitalized as an asset when incurred. Deferred financing costs in connection with all other debt arrangements are a direct deduction from the related debt liability when incurred. Deferred financing costs are amortized using the effective interest method over the term of the respective debt arrangement. This amortization expense is included in interest expense in the Consolidated Statements of Operations. Upon early termination or modification of a credit facility, all or a portion of unamortized fees related to such facility may be accelerated into interest expense. For extinguishments of the Company’s unsecured notes payable, any unamortized deferred financing costs are deducted from the carrying amount of the debt in determining the gain or loss from the extinguishment. Deferred Offering Costs: Legal fees and other costs incurred in connection with the Company’s shelf registration statement are capitalized as deferred offering costs in the Consolidated Statements of Assets and Liabilities. To the extent any such costs relate to equity offerings, these costs are charged as a reduction of capital upon utilization. To the extent any such costs relate to debt offerings, these costs are treated as deferred financing costs and are amortized over the term of the respective debt arrangement. Any deferred offering costs that remain at the expiration of the shelf registration statement or when it becomes probable that an offering will not be completed are expensed. Segment Reporting: The Company operates as a single reportable segment and derives revenues from investing primarily in originated loans and other securities, including broadly syndicated loans, of U.S. private companies and manages the business on a consolidated basis. The chief operating decision maker (“CODM”) is composed of the Company’s chief executive officer and chief financial officer. The primary performance metric provided to the CODM to assess performance and make operating decisions is "Net increase (decrease) in net assets resulting from operations" which is reported on the Consolidated Statement of Operations. Performance metrics are provided to the CODM on a quarterly basis and are utilized to evaluate performance generated from segment net assets. These key metrics, in addition to other factors, are utilized by the CODM to determine allocation of profits, such as for investment or the amount recommended to the Board for distribution to the Company’s shareholders. As the Company operates as a single reporting segment, the segment net assets are reported on the Consolidated Statements of Assets and Liabilities and the significant segment expenses are listed on the Consolidated Statement of Operations. Income Taxes: The Company has elected to be subject to tax as a RIC under Subchapter M of the Code and operates in a manner so as to qualify for the tax treatment applicable to RICs. In order to be subject to tax as a RIC, among other things, the Company is required to meet certain source of income and asset diversification requirements and timely distribute dividends to its stockholders of an amount generally at least equal to 90% of investment company taxable income, as defined by the Code and determined without regard to any deduction for dividends paid, for each taxable year. As a RIC, the Company is not subject to U.S. federal income tax on the portion of its taxable income and gains distributed currently to stockholders as a dividend. Depending on the level of taxable income earned during a taxable year, the Company may choose to retain taxable income in excess of current year dividend distributions and would distribute such taxable income in the next taxable year. The Company would then incur a 4% excise tax on such income, as required. To the extent that the Company determines that its estimated current year annual taxable income, determined on a calendar year basis, could exceed estimated current calendar year dividend distributions, the Company accrues excise tax, if any, on estimated excess taxable income as taxable income is earned. The Company anticipates timely distribution of its taxable income within the tax rules under Subchapter M of the Code. For calendar year 2023, the Company incurred $0.1 million of excise tax. The Company did not incur any U.S. federal excise tax for calendar year 2024. The Company does not expect to incur a U.S. federal excise tax for calendar year 2025. The Company holds certain portfolio investments through taxable subsidiaries. The purpose of the Company's taxable subsidiaries is to permit the Company to hold equity investments in portfolio companies which are "pass through" entities for U.S. federal income tax purposes in order to comply with the RIC tax requirements. The taxable subsidiaries are consolidated for financial reporting purposes, and portfolio investments held by them are included in the Company’s Consolidated Financial Statements as portfolio investments and recorded at fair value. The taxable subsidiaries are not consolidated with the Company for U.S. federal income tax purposes and may generate income tax expense, or benefit, and the related tax assets and liabilities, as a result of their ownership of certain portfolio investments. This income tax expense, if any, would be reflected in the Company's Consolidated Statements of Operations. The Company uses the liability method to account for its taxable subsidiaries' income taxes. Using this method, the Company recognizes deferred tax assets and liabilities for the estimated future tax effects attributable to temporary differences between financial reporting and tax bases of assets and liabilities. In addition, the Company recognizes deferred tax benefits associated with net operating loss carry forwards that it may use to offset future tax obligations. The Company measures deferred tax assets and liabilities using the enacted tax rates expected to apply to taxable income in the years in which it expects to recover or settle those temporary differences. FASB ASC Topic 740, Accounting for Uncertainty in Income Taxes ("ASC 740"), provides guidance for how uncertain tax positions should be recognized, measured, presented and disclosed in the Company's Consolidated Financial Statements. ASC 740 requires the evaluation of tax positions taken or expected to be taken in the course of preparing the Company's tax returns 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 the more-likely-than-not threshold are recorded as a tax benefit or expense in the current year. Management's determinations regarding ASC 740 may be subject to review and adjustment at a later date based upon factors including an ongoing analysis of tax laws, regulations and interpretations thereof. The Company recognizes the tax benefits of uncertain tax positions only where the position is "more-likely-than-not" to be sustained assuming examination by tax authorities. Management has analyzed the Company's tax positions and has concluded that no liability for unrecognized tax benefits should be recorded related to uncertain tax positions taken on returns filed for open tax years 2022, 2023 and 2024. The Company identifies its major tax jurisdictions as U.S. Federal and California, and the Company is not aware of any tax positions for which it is reasonably possible that the total amounts of unrecognized tax benefits will change materially in the next 12 months. Recent Accounting Pronouncements In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280), which improves reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. The amendments are effective for fiscal years beginning after December 15, 2023 and interim period within fiscal years beginning after December 15, 2024. The Company adopted ASU No. 2023-07 effective September 30, 2025 and concluded that the application of this guidance did not materially impact its consolidated financial statements. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures,” which requires additional disaggregated disclosures on the entity’s effective tax rate reconciliation and additional details on income taxes paid. The guidance is effective on a prospective basis, with the option for retrospective application, for annual periods beginning after December 15, 2024 and early adoption is permitted. The Company does not expect the adoption of ASU 2023-09 to have a material impact on its consolidated financial statements.

Oaktree Specialty Lending Corp 10-K