Firm Description William Blair is a global investment firm offering investment management and related services to clients. The firm was founded in 1935 and is registered with the SEC as both an investment adviser and a securities broker‐dealer. William Blair (a privately held company) is a wholly owned subsidiary of WBC Holdings, L.P., which is wholly owned by current William Blair employees (we also refer to employee owners as ‘partners’ in this Brochure). William Blair also is an affiliate of William Blair Investment Management, LLC, an investment adviser registered with the SEC (“WBIM”). WBIM provides institutional investment management business, separate from the other business lines within William Blair. William Blair is also an affiliate of SYSTM Wealth Solutions LLC (“SYSTM”), an investment adviser registered with the SEC. SYSTM operates a fee‐based platform which affiliated investment advisers (such as William Blair) can utilize to recommend, select, retain, fire and monitor sub‐managers and model providers. Investment Advisory Services William Blair’s private wealth management division (“PWM”) and its advisors (“PWM Advisors”) provide discretionary and non‐discretionary investment management services to clients for a fee. Clients pay us investment advisory fees based on fee schedules as described in Item 5. William Blair also manages accounts for wrap fee program clients. As a discretionary investment manager, we provide investment management services in accordance with each client’s investment guidelines. We accept investment restrictions from clients if the restrictions do not hinder our ability to execute our investment strategies and if such restrictions can be appropriately implemented. According to a client’s investment objectives and subject to reasonable investment restrictions, a PWM Advisor may elect to allocate all or a portion of that discretionary advisory client’s assets to one or more William Blair proprietary models (“William Blair Proprietary Home Office Models”). William Blair Proprietary Home Office Models are available through SYSTM. In certain cases, we provide investment guidance to clients on a non‐discretionary basis (on either a portion of the assets held in the account or the entire account) with the client making final investment decisions. William Blair provides non‐discretionary advisory services to other registered investment advisers by delivering model portfolios (“Non‐Discretionary Model Portfolio Program”). With respect to the Non‐Discretionary Model Portfolio Program, William Blair has no investment discretion, no knowledge of the underlying investment advisers’ clients, no authority to effect and/or execute trades on behalf of these registered investment advisers’ clients and no knowledge as to whether a registered investment adviser followed any of our non‐discretionary investment recommendations. We provide non‐discretionary investment advisory services to these registered investment advisers based on strategy model portfolios (similar to how we manage other separate accounts). William Blair has an indirect, minority‐ ownership interest in certain investment advisers that participate in the Non‐Discretionary Model Portfolio Program. Wrap Fee Program Clients William Blair serves as an investment manager to and sponsor of a comprehensive advisory fee program (also known as a wrap fee program), the “William Blair Wrap Program,” as described further in William Blair’s Form ADV 2A, Appendix 1, also known as our “William Blair Wrap Fee Program Brochure.” A wrap fee program is a program where a client is charged a specified “bundled” fee (generally, a percentage of assets under management) for discretionary investment management services and trade execution costs and sometimes other services such as custody, record keeping and reporting. In order to participate in a William Blair Wrap Program, an advisory client must maintain a brokerage account with William Blair, as introducing broker‐dealer. As described more fully below, Fidelity Investments and/or its various affiliates including but not limited to National Financial Services and Fidelity Brokerage Services (collectively, “NFS”) acts as clearing broker and provides custodial, clearing, settlement and certain other services for William Blair Wrap Program advisory clients. Our compensation under our William Blair Wrap Fee Program may be lower than our standard fee schedule; however, the overall cost of a wrap arrangement may be higher than a client otherwise would pay if the client paid our standard fee schedule and negotiated transaction costs and any other services (e.g., custody, record keeping and reporting) through a broker‐dealer. William Blair’s wrap program fees and standard advisory fees are negotiable. William Blair & Co., L.L.C. – Form ADV Part 2A – March 29, 2024 4 Platform Clients William Blair has entered into agreements with asset management platform providers, including with our affiliate, SYSTM (the “Platform”). PWM Advisors, for certain discretionary advisory account clients, access and hire discretionary investment advisers (the “Sub‐Managers”) or model providers (the “Model Providers”) through the Platforms. Some Platform providers and their underlying Sub‐Managers require information from clients, such as agreement to their standard terms & conditions, a client profile or application and other related documentation (including, in some instances, the opening of custodial and/or brokerage accounts). Your PWM Advisor will work with you to obtain any Platform required documentation. A client may impose reasonable restrictions on the management of account assets being managed on a Platform, such as, the designation of particular securities or types of securities that should not be purchased or that should

be sold if held in the account. As the client will not be able to communicate directly with any Sub‐Manager or Model Provider available through a Platform, the client should communicate these reasonable restrictions to their William Blair PWM Advisor. Sub Advisory Clients In some instances, certain entities hire William Blair to manage assets for their underlying clients. In these instances, William Blair acts in a sub‐advisory capacity. In some instances, William Blair has discretion to buy, sell and hold securities in the underlying clients’ accounts. In other instances, William Blair acts in a non‐discretionary capacity and the ultimate decision to buy, sell or hold securities is made by the registered investment adviser that hired William Blair. In some instances, the underlying client is able to communicate with William Blair while in other instances all communication is between William Blair and the entity. Sub‐Management Agreement with WBIM William Blair has entered into a Sub‐Management Agreement with its affiliate, WBIM. If authorized by the client, William Blair has the discretion to hire WBIM as a sub‐adviser to manage those allocated assets, with discretion (“WBIM Sub‐Advisory Accounts”). William Blair MB Investments Program William Blair established the “MB Investments Program” to provide select clients with access to certain investment opportunities generated through William Blair’s proprietary, global relationship network. William Blair MB Investments GP, LLC, a William Blair affiliate, (“MB General Partner”), serves as the general partner to William Blair MB Investments, L.P., a Delaware series limited partnership (“MB Partnership”). The MB Partnership’s investments were made in (a) other investment funds (such as private equity, debt, venture capital, and real estate) and (b) direct investments in private capital and business combination transactions including private company financings (ranging from early‐stage to late stage rounds), leveraged and unleveraged buyout transactions, and management buyout transactions (collectively, “MB Investments”). A new series will be formed to invest in each MB Investment (“Series”). An investor must independently and affirmatively elect to participate in the MB Investments Program and to invest in a Series and, if admitted as a limited partner, will receive interests in that Series (“Interests”). In some instances, a Series investor may be offered a co‐investment opportunity directly in a MB Investment or affiliate thereof (each a “Co‐Investment”). Interests in a MB Partnership Series are in Client’s name and ownership is recorded in the books and records of the MB Partnership. A Co‐Investment will be held in Client’s name and ownership will be recorded in the books and records of the Co‐Investment issuer. The MB Partnership is excluded from regulation under the Investment Company Act of 1940 and its securities are exempt from registration under the Securities Act of 1933. Accordingly, investors are not afforded the protections of those Acts. As discussed in the MB Partnership offering documents and in the non‐discretionary investment advisory agreement, the MB General Partner uses its good faith efforts to determine the fair market value of Interests. To the extent a client participates in the MB Investments Program or a Co‐Investment through a non‐discretionary investment William Blair & Co., L.L.C. – Form ADV Part 2A – March 29, 2024 5 advisory account, William Blair earns an investment advisory fee based on the fair market value of the Interests. Our affiliate, the MB General Partner, values the Interests. The higher the fair market value of the Interests or Co‐ Investment, the more William Blair earns in advisory fees, creating a conflict of interest. The MB General Partner can delegate to William Blair certain management and administrative responsibilities including the authority to select investment opportunities and make investment‐related decisions on behalf of the MB Partnership. Investment advice is provided directly to the MB Partnership and not individually to the limited partners. William Blair and PWM Advisors will not provide investment advice or recommendations to clients with respect to participation in the MB Investments Program or investing in any Series or Co‐Investment. A client independently decides to participate in the MB Investments Program and affirmatively elects to purchase Interests in each MB Partnership Series or to invest in a Co‐Investment. A Series limited partner can contribute capital through a brokerage account, advisory account, bank account or otherwise. Once the client invests in any Series or Co‐Investment through a non‐discretionary advisory account, William Blair will provide asset allocation, monitoring and performance reporting. Information regarding limited partner eligibility, fees, expenses, risks, conflicts of interest and terms and conditions are set forth in the MB Partnership offering documents, any Co‐Investment offering documents as well as highlighted in this Brochure. Proxy Voting, Corporate Actions and Other Legal Matters Clients have the option of voting proxies directly or delegating proxy voting discretion to William Blair or a third party. In cases where William Blair has proxy voting discretion, Institutional Shareholder Services, Inc. (“ISS”) provides proxy voting, maintenance, reporting, analysis and recordkeeping services for William Blair with respect to proxies for companies whose securities are managed by William Blair on a discretionary basis. Assets under Management As of December 31, 2023, William Blair had approximately $49.9 billion in assets under management, of which, we managed approximately 92% on a discretionary basis and 8% on a non‐discretionary basis.