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FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below. Shareholder Fees (fees paid directly from your investment): 0 0 0 0 0 0 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment): 0.0085 0.0085 0.0085 0.0025 0 0 0.0088 0.0087 0.0078 0.0198 0.0172 0.0163 0.0083 0.0082 0.0078 0.0115 0.0090 0.0085 March 5, 2027 Example: This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 117 541 991 2239 92 462 856 1962 87 438 813 1867 Portfolio Turnover: The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;">higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 81% of the average value of its portfolio.</div> 0.81 PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its total assets in a portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes worldwide that the Adviser believes have above-average growth, profitability and quality characteristics. The Adviser seeks investment opportunities in companies at different stages of development, ranging from large, well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. The use of the term “global” in the Fund’s name is meant to emphasize that the Adviser looks for investment opportunities on a worldwide basis and the investment strategy is not constrained by the countries or regions in which companies are located. The Fund’s investments are normally allocated among at least five different countries. The Fund may invest in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.The Adviser will vary the Fund’s sector and geographic diversification based upon the Adviser’s ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Adviser will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.THE FUND IS NON‑DIVERSIFIED UNDER THE INVESTMENT COMPANY ACT OF 1940, AS AMENDED, AND MAY INVEST A LARGER PERCENTAGE OF ITS ASSETS IN FEWER ISSUERS THAN DIVERSIFIED MUTUAL FUNDS. The Fund’s returns will vary, and you could lose money by investing in the Fund. <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Equity Funds General Risk.</span> The value of equity securities the Fund holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Market Risk.</span> The value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably. The value of an investment may decline due to factors affecting securities markets generally or particular industries represented in the securities markets. The value of an investment may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, recessions, inflation, rapid interest rate changes, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Events such as war,</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;">geopolitical risk, acts of terrorism, social unrest, tariffs and other restrictions on trade, natural disasters, the spread of infectious illness or other public health threats, or the threat or potential of one or more such events and developments could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Foreign Investment Risk.</span> The risks of foreign investments may include less publicly available information, less stringent investor protections and disclosure standards, less governmental regulation and supervision of foreign stock exchanges, brokers and issuers, share registration and custody, a lack of uniform accounting, auditing and financial reporting standards, practices and requirements, the possibility of expropriation, seizure or nationalization, confiscatory taxation, limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding or other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect the Fund’s investments. Foreign investments may be less liquid and their prices more volatile than the securities of U.S. companies. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Currency Risk.</span> The value of the Fund’s portfolio may be affected by changes in exchange rates or control regulations. Currency exchange rates may fluctuate significantly over short periods of time for a number of reasons, including changes in interest rates. If a local currency gains against the U.S. dollar, the value of the security increases in U.S. dollar terms. If a local currency declines against the U.S. dollar, the value of the security decreases in U.S. dollar terms.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Emerging Markets Risk.</span> Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Geographic Risk.</span> To the extent that the Fund invests a significant portion of its assets in any one country or geographic region, the Fund will be subject to greater risk of loss or volatility than if the Fund always maintained wide geographic diversity among the countries and geographic regions in which it invests. Investing in any one country or geographic region makes the Fund more vulnerable to the risks of adverse securities markets, exchange rates and social, political, regulatory and economic events in that one country or geographic region.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Smaller Company Risk.</span> Stocks of smaller companies involve greater risk than those of larger, more established companies. This is because smaller companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of smaller companies may be more volatile and less liquid than securities of large-capitalized companies</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Share Ownership Concentration Risk.</span> To the extent that a significant portion of the Fund’s shares is held by a limited number of shareholders or their affiliates, there is a risk that the share trading activities of these shareholders could disrupt the Fund’s investment strategies, which could have adverse consequences for the Fund and other shareholders (e.g., by requiring the Fund to sell investments at inopportune times or causing the Fund to maintain larger-than-expected cash positions pending acquisition of investments).</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Non‑Diversification Risk.</span> The Fund is non‑diversified, meaning that it is permitted to invest a larger percentage of its assets in fewer issuers than diversified mutual funds. Thus, the Fund may be more susceptible to adverse developments affecting any single issuer held in its portfolio, and may be more susceptible to greater losses because of these developments.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Style Risk.</span> Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Focus Risk.</span> To the extent that the Fund focuses its investments in particular industries, asset classes or sectors of the economy, any market changes affecting companies in those industries, asset classes or sectors may impact the Fund’s performance.</div> <div style="margin-top: 0pt; margin-bottom: 0pt; font-size: 10pt; font-family: times new roman;"><span style="font-weight: bold;">Operational and Technology Risk.</span> Cyber-attacks, disruptions, or failures that affect the Fund’s service providers, counterparties, market participants, or issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.</div> FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance that is generally representative of the market sectors or types of investments in which the Fund invests. On January 27, 2026, the Fund’s benchmark changed from the MSCI All Country World Investable Market Index (net) to the MSCI All Country World Index (net). The primary reason for this change is to compare the Fund to a benchmark that more closely reflects the market and portfolio composition focus the Fund uses in its investment strategy. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to https://im.williamblair.com/investments/mutual-funds or call 1‑800‑635‑2886. The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance that is generally representative of the market sectors or types of investments in which the Fund invests. On January 27, 2026, the Fund’s benchmark changed from the MSCI All Country World Investable Market Index (net) to the MSCI All Country World Index (net). The primary reason for this change is to compare the Fund to a benchmark that more closely reflects the market and portfolio composition focus the Fund uses in its investment strategy. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. https://im.williamblair.com/investments/mutual-funds 1‑800‑635‑2886 Annual Total Returns. The bar chart below provides an illustration of how the Fund’s Class N shares performance has varied in each of the last ten calendar years. Highest Quarterly Return Highest Quarterly Return24.59%(<span class="sec-hidden" style="-sec-ix-hidden: t_76_443eebe6_9d9e_5b85_b1e9_ae72cb812c2b;">2Q20</span>)Lowest QuarterlyReturn(19.72)%(<span class="sec-hidden" style="-sec-ix-hidden: t_76_7051831b_70d1_e2d4_7995_9095346134a2;">2Q22</span>) 0.2459 Lowest QuarterlyReturn -0.1972 Average Annual Total Returns(For the periods ended December 31, 2025). The table below shows returns on a before‑tax and after‑tax basis for Class N shares and on a before‑tax basis for Class I and Class R6 shares. After‑tax returns for Class I and Class R6 shares will vary. After‑tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after‑tax returns depend on an investor’s tax situation and maydiffer from those shown. After‑tax returns are not relevant to investors who hold their Fund shares through tax‑deferred arrangements, such as 401(k) plans or individual retirement accounts. The table below shows returns on a before‑tax and after‑tax basis for Class N shares and on a before‑tax basis for Class I and Class R6 shares. After‑tax returns for Class I and Class R6 shares will vary. After‑tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. After‑tax returns are not relevant to investors who hold their Fund shares through tax‑deferred arrangements, such as 401(k) plans or individual retirement accounts. 0.1482 0.0446 0.0998 0.0189 -0.0045 0.0656 0.1769 0.0316 0.0780 0.1520 0.0474 0.1028 0.1523 0.0479 0.1034 0.2234 0.1119 0.1172 0.2206 0.1075 0.1145 William Blair Investment Management, LLC (the “Adviser”) has entered into a contractual agreement with the Fund to waive fees and/or reimburse expenses in order to limit the Fund’s operating expenses (excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of the Fund’s business) to 1.15%, 0.90% and 0.85% of average daily net assets for Class N, Class I and Class R6 shares, respectively, until March 5, 2027. The Adviser may not terminate this arrangement prior to March 5, 2027 without the approval of the Fund’s Board of Trustees.