2024 GBDC 代理提醒信 p. 1 您的投票很重要 尊敬的股東： 根據我們的最新記錄，我們尚未收到您對將於 2024 年 5 月 29 日星期三舉行的 Golub Capital BDC, Inc.（“GBDC” 或 “公司”）股東特別會議的投票指示，該特別會議將於 2024 年 5 月 29 日星期三舉行，與 GBDC 提議與 GBDC 的 合併 Olub Capital BDC 3, Inc.（“GBDC 3”）。 無論您持有多少股票，您的投票都非常重要。 我的緊迫感部分源於我對擬議的合併將為股東帶來的好處感到興奮。 GBDC董事會，包括所有獨立董事，一致建議股東對 與合併相關的提案投贊成票。 您對該提案的投票將通過以下預期收益為GBDC股東創造有意義的價值： — 擴大規模和流動性 — 穩定的投資策略 — 改善費用結構 — 預計獲得長期、低成本、靈活債務資本的機會將更廣泛 — 淨資產價值（“NAV”）增加的潛力 現在的投票將使我們能夠完成股票特別會議的業務 GBDC的持有者毫不拖延。如果您需要 協助對股票進行投票，請致電GBDC的代理律師布羅德里奇，免費撥打1-844-853-0928。 謝謝， David B. Golub 首席執行官 四種投票方式 使用智能手機 攝像頭 掃描隨附的 代理卡/VIF 上的快速響應 代碼或 “二維碼”，然後 點擊出現的鏈接。 投票處理 標記您的 選票並註明日期，然後將其放入提供的 已付郵資信封 中退回。 沒有代理卡的郵件 在美國東部時間週一至週五上午 9:00 至晚上 9:00 致電 1-844-853-0928 與代理專家交談 。 使用代理卡 使用 按鍵式電話致電 1-800-690-6903 使用自動系統投票 。 電話 WWW.PROXYVOTE.COM 訪問 網站時請準備好代理卡 。有一些易於遵循的説明可幫助您 填寫電子 投票説明表。 在線二維碼 R88605-LTR

2024 年 GBDC 代理提醒函 第 2 頁擴大規模和流動性：擬議的合併將顯著增加 GBDC 的規模，其 總資產預計將從約 57 億美元增加到約 85 億美元。1 與獨立公司相比，GBDC 市值的增加預計將提供更大的交易 流動性和更大的機構所有權潛力。 該交易還有望通過消除多餘開支來實現運營協同效應。 一致的投資策略：合併後的投資組合預計將與GBDC目前的投資組合基本相似，因為GBDC 3的投資中有99％以上與GBDC.1的投資重疊。收盤後，GBDC預計將繼續保持自2010年首次公開募股 以來所遵循的相同投資策略：專注於向通常由私募股權公司擁有的 彈性行業的美國中間市場公司提供第一留置權優先擔保和一站式貸款。 改善費用結構：為了支持擬議的合併，GBDC的投資顧問GC Advisors LLC（“GC Advisors”）已同意將收入激勵費和資本收益激勵費 利率從20.0％降至15.0％。2 GBDC的1.0％的基本管理費率、累計激勵費上限、 自成立以來的回顧期和每年8％的收入激勵費障礙率將全部降至8％ 保持 原位。 預計獲得長期、低成本、靈活債務資本的渠道將更廣泛：作為一家獨立的 公司，合併後的公司 預計能夠獲得比GBDC更廣泛的債務融資解決方案，並且由於合併後的公司 擴大規模，包括可能在投資級無抵押債務市場中獲得更具吸引力的條款。 淨資產價值（“NAV”）增長潛力：如果合併結束時GBDC的交易價格高於資產淨值，則交換比率結構有可能增加GBDC的每股資產淨值（“NAV”）。 交易理由 敦促股東立即對該提案投票 “贊成” 無論您擁有多少股票，您的投票都很重要。 如果您對如何投票股票還有其他疑問，或者需要協助對股票進行投票， 請致電GBDC的代理律師： Broadridge | 1-844-853-0928 董事會一致批准了與GBDC 3合併的協議和新的投資諮詢協議。 董事會一致建議 GBDC 股東投票支持 所附委託書中描述的合併股票發行提案。 欲瞭解更多信息，請訪問我們網站主頁上的投資者資源——活動/演示鏈接 www.golubcapitalbdc.com，參閲標題為 “與Golub Capital BDC 3, Inc.的擬議合併概述 的演示文稿以及特別會議委託書中描述的提案全文。 1。基於GBDC和GBDC 3截至2023年12月31日的合併財務狀況表。 2。激勵費的減少將在合併結束時永久生效，並將自2024年1月1日起生效，因為GC Advisors已同意在合併待定期間單方面免除15.0％以上的激勵費 。GBDC的累積激勵費上限、自成立以來的回顧期和每年 8％的收入激勵費門檻率都將保持不變。

2024 GBDC Proxy Reminder Letter p. 3 DISCLOSURES Forward-Looking Statements This communication may contain “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. Statements other than statements of historical facts included in this communication may constitute forward-looking statements and are not guarantees of future performance or results and involve a number of risks and uncertainties. Actual results may differ materially from those expressed or implied in the forward-looking statements as a result of a number of factors, including those described from time to time in filings with the Securities and Exchange Commission. GBDC and GBDC 3 undertake no duty to update any forward-looking statement made herein. All forward-looking statements speak only as of the date of this communication. Some of the statements in this communication constitute forward-looking statements because they relate to future events, future performance or financial condition or the two-step merger of GBDC 3 with and into GBDC (collectively, the “Mergers”), along with the related proposals for which stockholder approval will be sought (collectively, the “Proposals”). The forward-looking statements may include statements as to: future operating results of GBDC and GBDC 3 and distribution projections; business prospects of GBDC and GBDC 3 and the prospects of their portfolio companies; the potential benefits of the Mergers; and the impact of the investments that GBDC and GBDC 3 expect to make. In addition, words such as “may,” “might,” “will,” “intend,” “should,” “could,” “can,” “would,” “expect,” “believe,” “estimate,” “anticipate,” “predict,” “potential,” “plan” or similar words indicate forward-looking statements, although not all forward-looking statements include these words. The forward-looking statements contained in this communication involve risks and uncertainties. Certain factors could cause actual results and conditions to differ materially from those projected, including the uncertainties associated with (i) the timing or likelihood of the Mergers closing; (ii) the expected synergies and savings associated with the Mergers; (iii) the ability to realize the anticipated benefits of the Mergers, including the expected elimination of certain expenses and costs due to the Mergers; (iv) the percentage of GBDC and GBDC 3 stockholders voting in favor of the proposals submitted for their approval; (v) the possibility that competing offers or acquisition proposals will be made; (vi) the possibility that any or all of the various conditions to the consummation of the Mergers may not be satisfied or waived; (vii) risks related to diverting management’s attention from ongoing business operations; (viii) the risk that stockholder litigation in connection with the Mergers may result in significant costs of defense and liability; (ix) changes in the economy, financial markets and political environment, including the impacts of inflation and rising interest rates; (x) risks associated with possible disruption in the operations of GBDC and GBDC 3 or the economy generally due to terrorism, war or other geopolitical conflict (including the current conflict between Russia and Ukraine), natural disasters or global health pandemics, such as the COVID-19 pandemic; (xi) future changes in laws or regulations (including the interpretation of these laws and regulations by regulatory authorities); (xii) changes in political, economic or industry conditions, the interest rate environment or conditions affecting the financial and capital markets that could result in changes to the value of GBDC’s or GBDC 3’s assets; (xiii) elevating levels of inflation, and its impact on GBDC and GBDC 3, on their portfolio companies and on the industries in which they invest; (xiv) the combined company’s plans, expectations, objectives and intentions, as a result of the Mergers; (xv) the future operating results and net investment income projections of GBDC, GBDC 3, or, following the closing of one or both of the Mergers, the combined company; (xvi) the ability of GC Advisors to locate suitable investments for the combined company and to monitor and administer its investments; (xvii) the ability of GC Advisors or its affiliates to attract and retain highly talented professionals; (xviii) the business prospects of GBDC, GBDC 3 or, following the closing of one or both of the Mergers, the combined company and the prospects of their portfolio companies; (xix) the impact of the investments that GBDC, GBDC 3 or, following the closing of one or both of the Mergers, the combined company expect to make; (xx) the expected financings and investments and additional leverage that GBDC, GBDC 3 or, following the closing of one or both of the Mergers, the combined company may seek to incur in the future; and (xxi) other considerations that may be disclosed from time to time in GBDC’s and GBDC 3’s publicly disseminated documents and filings. GBDC and GBDC 3 have based the forward-looking statements included in this press release on information available to them on the date of this communication, and they assume no obligation to update any such forward-looking statements. Although GBDC and GBDC 3 undertake no obligation to revise or update any forward-looking statements, whether as a result of new information, future events or otherwise, you are advised to consult any additional disclosures that they may make directly to you or through reports that GBDC and GBDC 3 in the future may file with the SEC, including the Joint Proxy Statement (each as defined below), annual reports on Form 10-K, quarterly reports on Form 10-Q and current reports on Form 8-K. Additional Information and Where to Find It This communication relates to a proposed business combination involving GBDC and GBDC 3, along with the related Proposals for which stockholder approval will be sought. In connection with the Proposals, each of GBDC and GBDC 3 intend to file relevant materials with the SEC, including a registration statement on Form N-14, which will include a joint proxy statement of GBDC and GBDC 3 and a prospectus of GBDC (the “Joint Proxy Statement”). This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act. STOCKHOLDERS OF EACH OF GBDC AND GBDC 3 ARE URGED TO READ ALL RELEVANT DOCUMENTS FILED WITH THE SEC, INCLUDING THE JOINT PROXY STATEMENT OF GBDC AND GBDC 3 REGARDING THE PROPOSALS, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS THERETO, BECAUSE THEY CONTAIN IMPORTANT INFORMATION ABOUT GBDC, GBDC 3, THE MERGERS AND THE PROPOSALS. Investors and security holders will be able to obtain the documents filed with the SEC free of charge at the SEC’s web site, http://www.sec.gov or, for documents filed by GBDC, from GBDC’s website at http://www.golubcapitalbdc.com. Participants in the Solicitation GBDC and GBDC 3 and their respective directors, executive officers and certain other members of management and employees of GC Advisors and its affiliates, may be deemed to be participants in the solicitation of proxies from the stockholders of GBDC and GBDC 3 in connection with the Proposals. Information regarding the persons who may, under the rules of the SEC, be considered participants in the solicitation of the GBDC and GBDC 3 stockholders in connection with the Proposals will be contained in the Proxy Statement when such document becomes available. This document may be obtained free of charge from the sources indicated above.