2024 GBDC 代理提醒信 p. 1 您的投票很重要 尊敬的股东： 根据我们的最新记录，我们尚未收到您对将于 2024 年 5 月 29 日星期三举行的 Golub Capital BDC, Inc.（“GBDC” 或 “公司”）股东特别会议的投票指示，该特别会议将于 2024 年 5 月 29 日星期三举行，与 GBDC 提议与 GBDC 的 合并 Olub Capital BDC 3, Inc.（“GBDC 3”）。 无论您持有多少股票，您的投票都非常重要。 我的紧迫感部分源于我对拟议的合并将为股东带来的好处感到兴奋。 GBDC董事会，包括所有独立董事，一致建议股东对 与合并相关的提案投赞成票。 您对该提案的投票将通过以下预期收益为GBDC股东创造有意义的价值： — 扩大规模和流动性 — 稳定的投资策略 — 改善费用结构 — 预计获得长期、低成本、灵活债务资本的机会将更广泛 — 净资产价值（“NAV”）增加的潜力 现在的投票将使我们能够完成股票特别会议的业务 GBDC的持有者毫不拖延。如果您需要 协助对股票进行投票，请致电GBDC的代理律师布罗德里奇，免费拨打1-844-853-0928。 谢谢， David B. Golub 首席执行官 四种投票方式 使用智能手机 摄像头 扫描随附的 代理卡/VIF 上的快速响应 代码或 “二维码”，然后 点击出现的链接。 投票处理 标记您的 选票并注明日期，然后将其放入提供的 已付邮资信封 中退回。 没有代理卡的邮件 在美国东部时间周一至周五上午 9:00 至晚上 9:00 致电 1-844-853-0928 与代理专家交谈 。 使用代理卡 使用 按键式电话致电 1-800-690-6903 使用自动系统投票 。 电话 WWW.PROXYVOTE.COM 访问 网站时请准备好代理卡 。有一些易于遵循的说明可帮助您 填写电子 投票说明表。 在线二维码 R88605-LTR

2024 年 GBDC 代理提醒函 第 2 页扩大规模和流动性：拟议的合并将显著增加 GBDC 的规模，其 总资产预计将从约 57 亿美元增加到约 85 亿美元。1 与独立公司相比，GBDC 市值的增加预计将提供更大的交易 流动性和更大的机构所有权潜力。 该交易还有望通过消除多余开支来实现运营协同效应。 一致的投资策略：合并后的投资组合预计将与GBDC目前的投资组合基本相似，因为GBDC 3的投资中有99％以上与GBDC.1的投资重叠。收盘后，GBDC预计将继续保持自2010年首次公开募股 以来所遵循的相同投资策略：专注于向通常由私募股权公司拥有的 弹性行业的美国中间市场公司提供第一留置权优先担保和一站式贷款。 改善费用结构：为了支持拟议的合并，GBDC的投资顾问GC Advisors LLC（“GC Advisors”）已同意将收入激励费和资本收益激励费 利率从20.0％降至15.0％。2 GBDC的1.0％的基本管理费率、累计激励费上限、 自成立以来的回顾期和每年8％的收入激励费障碍率将全部降至8％ 保持 原位。 预计获得长期、低成本、灵活债务资本的渠道将更广泛：作为一家独立的 公司，合并后的公司 预计能够获得比GBDC更广泛的债务融资解决方案，并且由于合并后的公司 扩大规模，包括可能在投资级无抵押债务市场中获得更具吸引力的条款。 净资产价值（“NAV”）增长潜力：如果合并结束时GBDC的交易价格高于资产净值，则交换比率结构有可能增加GBDC的每股资产净值（“NAV”）。 交易理由 敦促股东立即对该提案投票 “赞成” 无论您拥有多少股票，您的投票都很重要。 如果您对如何投票股票还有其他疑问，或者需要协助对股票进行投票， 请致电GBDC的代理律师： Broadridge | 1-844-853-0928 董事会一致批准了与GBDC 3合并的协议和新的投资咨询协议。 董事会一致建议 GBDC 股东投票支持 所附委托书中描述的合并股票发行提案。 欲了解更多信息，请访问我们网站主页上的投资者资源——活动/演示链接 www.golubcapitalbdc.com，参阅标题为 “与Golub Capital BDC 3, Inc.的拟议合并概述 的演示文稿以及特别会议委托书中描述的提案全文。 1。基于GBDC和GBDC 3截至2023年12月31日的合并财务状况表。 2。激励费的减少将在合并结束时永久生效，并将自2024年1月1日起生效，因为GC Advisors已同意在合并待定期间单方面免除15.0％以上的激励费 。GBDC的累积激励费上限、自成立以来的回顾期和每年 8％的收入激励费门槛率都将保持不变。

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.