Strategy. Normally investing primarily in equity securities. Normally investing at least 80% of assets in securities of companies that Fidelity Management & Research Company LLC (FMR) (the Adviser) believes have proven or improving sustainability practices based on an evaluation of such companies' individual environmental, social and governance (ESG) profile. In general, the Adviser favors those companies it believes are well positioned to further improve their demonstrated ESG profile in the future. Using the Adviser's proprietary ESG ratings process to evaluate the current state of an issuer's sustainability practices using a data-driven framework that includes both proprietary and third-party data, and also provide a qualitative forward-looking assessment of an issuer's sustainability outlook provided by the Adviser's fundamental research analysts and ESG team. … Show more… Normally investing primarily in equity securities. Normally investing at least 80% of assets in securities of companies that Fidelity Management & Research Company LLC (FMR) (the Adviser) believes have proven or improving sustainability practices based on an evaluation of such companies' individual environmental, social and governance (ESG) profile. In general, the Adviser favors those companies it believes are well positioned to further improve their demonstrated ESG profile in the future. Using the Adviser's proprietary ESG ratings process to evaluate the current state of an issuer's sustainability practices using a data-driven framework that includes both proprietary and third-party data, and also provide a qualitative forward-looking assessment of an issuer's sustainability outlook provided by the Adviser's fundamental research analysts and ESG team. The Adviser's ESG ratings of issuers are derived from multiple factors, including an issuer's environmental profile, which may include, but is not limited to, carbon and toxic emissions, water management, waste management, vulnerability to the physical impacts of climate change, and research and investment into products, services, and energies that reduce emissions and/or provide opportunities to transition to less carbon-intensive products or operations. An assessment of an issuer's social profile includes, but is not limited to, its approach to diversity and inclusion, human capital management, data privacy, product safety and human rights. With respect to governance, the independence and diversity of an issuer's board, its compensation practices and board oversight of critical ESG issues are considered as part of the assessment. These factors are weighted based on how material the Adviser believes each factor is to an issuer's financial outlook, and not all factors may be applicable to all issuers. Investing in issuers that the Adviser believes deliver tangible environmental or social impact through core business operations. An assessment of the impact characteristics of an issuer may involve corporate engagement and an analysis of issuer alignment with the United Nations Sustainable Development Goals using qualitative analysis as well as proprietary or third-party data. For example, issuers that provide access to clean water, education, or clean energy through their core business may be considered to deliver tangible impact. Investing in securities of domestic and foreign issuers. In addition to the ESG ratings process, using fundamental analysis of factors such as each issuer's financial condition and industry position, as well as market and economic conditions, to select investments. Employing sustainable investing exclusion criteria to avoid investments in issuers that are directly engaged in, and/or derive significant revenue from, certain industries. Please see "Fund Basics - Investment Details - Sustainable Investing Exclusions" for additional information. Reorganization. The Board of Trustees of Fidelity Summer Street Trust has unanimously approved an Agreement and Plan of Reorganization ("Agreement") between Fidelity SAI Sustainable Future Fund and Fidelity SAI Sustainable U.S. Equity Fund. Each fund seeks long-term growth of capital. As a result of the proposed Reorganization, shareholders of Fidelity SAI Sustainable Future Fund would receive shares of Fidelity SAI Sustainable U.S. Equity Fund. The Agreement provides for the transfer of all of the assets of Fidelity SAI Sustainable Future Fund in exchange for shares of Fidelity SAI Sustainable U.S. Equity Fund equal in value to the net assets of Fidelity SAI Sustainable Future Fund and the assumption by Fidelity SAI Sustainable U.S. Equity Fund of all of the liabilities of Fidelity SAI Sustainable Future Fund. After the exchange, Fidelity SAI Sustainable Future Fund will distribute Fidelity SAI Sustainable U.S. Equity Fund shares to its shareholders pro rata, in liquidation of Fidelity SAI Sustainable Future Fund. As a result, shareholders of Fidelity SAI Sustainable Future Fund will become shareholders of Fidelity SAI Sustainable U.S. Equity Fund (these transactions are collectively referred to as the "Reorganization"). Shareholders of Fidelity SAI Sustainable Future Fund will receive a combined information statement and prospectus containing more information with respect to the Reorganization, and a summary of the Board's considerations in approving the Agreement. The Reorganization, which does not require shareholder approval, is expected to take place on or about November 15, 2024. The Reorganization is expected to be atax-freetransaction. This means that neither Fidelity SAI Sustainable Future Fund nor its shareholders will recognize any gain or loss as a direct result of the Reorganization. In connection with the Reorganization, an information statement/prospectus that will be included in a registration statement on FormN-14will be filed with the Securities and Exchange Commission. After the registration statement is filed with the SEC, it may be amended or withdrawn and the information statement/prospectus will not be distributed to shareholders of Fidelity SAI Sustainable Future Fund unless and until the registration statement becomes effective. Shareholders should read the information statement/prospectus, which contains important information about the Reorganization, when it becomes available. For a free copy of the information statement/prospectus, please contact Fidelity at1-800-544-3455.The information statement/prospectus will also be available on the Securities and Exchange Commission's website (www.sec.gov). For more detailed information, please contact Fidelity at1-800-544-3455. Show less