APRIL 30, 2021 2021 Semi-Annual Report (Unaudited) BlackRock Multi-Sector Income Trust (BIT) Not FDIC Insured • May Lose Value • No Bank Guarantee Supplemental Information (unaudited) Section 19(a) Notices BlackRock Multi-Sector Income Trust’s (BIT) (the "Trust") amounts and sources of distributions reported are estimates and are being provided to you pursuant to regulatory requirements and are not being provided for tax reporting purposes. The actual amounts and sources for tax reporting purposes will depend upon the Trust’s investment experience during the remainder of its fiscal year and may be subject to changes based on tax regulations. The Trust will provide a Form 1099-DIV each calendar year that will tell you how to report these distributions for U.S. federal income tax purposes. April 30, 2021 Total Cumulative Distributions % Breakdown of the Total Cumulative for the Fiscal Period Distributions for the Fiscal Period Net Realized Net Realized Total Per Net Realized Net Realized Total Per Net Capital Gains Capital Gains Return of Common Net Capital Gains Capital Gains Return of Common Trust Name Income Short-Term Long-Term Capital (a) Share Income Short-Term Long-Term Capital Share BIT .............................. $ 0.506309 $ — $ — $ 0.235891 $ 0.742200 68% —% —% 32% 100% (a) The Trust estimates that it has distributed more than its net income and net realized capital gains; therefore, a portion of the distribution may be a return of capital. A return of capital may occur, for example, when some or all of the shareholder’s investment in the Trust is returned to the shareholder. A return of capital does not necessarily reflect the Trust’s investment performance and should not be confused with “yield” or “income.” When distributions exceed total return performance, the difference will reduce the Trust’s net asset value per share. Section 19(a) notices for the Trust, as applicable, are available on the BlackRock website at blackrock.com. Section 19(b) Disclosure The Trust, acting pursuant to a U.S. Securities and Exchange Commission (“SEC”) exemptive order and with the approval of the Trust’s Board of Trustees (the “Board”), has adopted a managed distribution plan, consistent with its investment objectives and policies to support a level distribution of income, capital gains and/or return of capital (the “Plan”). In accordance with the Plan, the Trust currently distributes the following fixed amounts per share on a monthly basis: Amount Per Exchange Symbol Common Share BIT............................................................................................................................................................. $ 0.1237 The fixed amounts distributed per share are subject to change at the discretion of the Trust’s Board. Under its Plan, the Trust will distribute all available net income to its shareholders as required by the Internal Revenue Code of 1986, as amended (the “Code”). If sufficient income (inclusive of net income and short-term capital gains) is not earned on a monthly basis, the Trust will distribute long-term capital gains and/or return of capital to shareholders in order to maintain a level distribution. Each monthly distribution to shareholders is expected to be at the fixed amount established by the Board; however, the Trust may make additional distributions from time to time, including additional capital gain distributions at the end of the taxable year, if required to meet requirements imposed by the Code and/or the Investment Company Act of 1940, as amended (the “1940 Act”). Shareholders should not draw any conclusions about the Trust’s investment performance from the amount of these distributions or from the terms of the Plan. The Trust’s total return performance is presented in its financial highlights table. The Board may amend, suspend or terminate the Trust’s Plan at any time without prior notice to the Trust’s shareholders if it deems such actions to be in the best interests of the Trust or its shareholders. The suspension or termination of the Plan could have the effect of creating a trading discount (if the Trust’s stock is trading at or above net asset value) or widening an existing trading discount. The Trust is subject to risks that could have an adverse impact on its ability to maintain level distributions. Examples of potential risks include, but are not limited to, economic downturns impacting the markets, changes in interest rates, decreased market volatility, companies suspending or decreasing corporate dividend distributions and changes in the Code. 2 2021 B LACKR OCK S EMI-ANNUAL R EPORT TO S HAREHOLDERS The Markets in Review Dear Shareholder, The 12-month reporting period as of April 30, 2021 reflected a remarkable period of adaptation and recovery, as the global economy dealt with the implications of the coronavirus (or “COVID-19”) pandemic. As the period began, the response to the virus’s spread was well underway, and countries around the world felt the effect of economically disruptive countermeasures. Stay-at-home orders and closures of non-essential businesses were imposed in many parts of the world, workers were laid off, and unemployment claims spiked, causing a global recession. As May 2020 began, stocks had just begun to recover from the lowest point following the onset of the pandemic. This recovery continued throughout the reporting period, as businesses continued re-opening and Rob Kapito governments learned to adapt to life with the virus. Equity prices rose through the summer, fed by strong fiscal President, BlackRock Advisors, LLC and monetary support and improving economic indicators. The implementation of mass vaccination campaigns and passage of an additional $1.9 trillion of fiscal stimulus further boosted stocks, and many equity indices neared or surpassed all-time highs late in the reporting period. In the United States, both large- and small-capitalization stocks posted a significant advance. International equities also gained, as both developed Total Returns as of April 30, 2021 countries and emerging markets rebounded substantially. 6-Month 12-Month U.S. large cap equities 28.85% 45.98% The 10-year U.S. Treasury yield (which is inversely related to bond prices) had fallen sharply prior to the (S&P 500 Index) beginning of the reporting period, which meant bonds were priced for extreme risk avoidance and economic U.S. small cap equities disruption. Despite expectations of doom and gloom, the economy expanded rapidly, stoking inflation concerns 48.06 74.91 (Russell 2000 Index) late in the reporting period, which led to higher yields and a negative overall return for most U.S. Treasuries. In the corporate bond market, support from the U.S. Federal Reserve (the “Fed”) assuaged credit concerns and International equities led to substantial returns for high-yield corporate bonds, although investment-grade corporates declined (MSCI Europe, Australasia, 28.84 39.88 Far East Index) slightly. Emerging market equities 22.95 48.71 The Fed remained committed to accommodative monetary policy by maintaining near zero interest rates and (MSCI Emerging Markets Index) by announcing that inflation could exceed its 2% target for a sustained period without triggering a rate increase. 3-month Treasury bills To stabilize credit markets, the Fed also continued purchasing significant quantities of bonds, as did other (ICE BofA 3-Month 0.05 0.11 influential central banks around the world, including the European Central Bank and the Bank of Japan. U.S. Treasury Bill Index) U.S. Treasury securities Looking ahead, while coronavirus-related disruptions have clearly hindered worldwide economic growth, we (ICE BofA 10-Year (6.26) (7.79) believe that the global expansion will continue to accelerate as vaccination efforts ramp up and pent-up U.S. Treasury Index) consumer demand leads to higher spending. While we expect inflation to increase somewhat as the expansion U.S. investment grade bonds continues, we believe the recent uptick owes more to temporary supply disruptions than a lasting change in (Bloomberg Barclays (1.52) (0.27) fundamentals. The change in Fed policy also means that moderate inflation is less likely to be followed by U.S. Aggregate Bond Index) interest rate hikes that could threaten the economic expansion. Tax-exempt municipal bonds 2.42 7.40 Overall, we favor a positive stance toward risk, with an overweight in equities. We see U.S. and Asian equities (S&P Municipal Bond Index) outside of Japan benefiting from structural growth trends in technology, while emerging markets should be U.S. high yield bonds (Bloomberg Barclays particularly helped by a vaccine-led economic expansion. While we are underweight overall on credit, global 7.98 19.57 high-yield and Asian bonds present attractive opportunities. We believe that international diversification and a U.S. Corporate High Yield 2% focus on sustainability can help provide portfolio resilience, and the disruption created by the coronavirus Issuer Capped Index) appears to be accelerating the shift toward sustainable investments. Past performance is not an indication of future results. Index performance is shown for illustrative purposes only. You In this environment, our view is that investors need to think globally, extend their scope across a broad array of cannot invest directly in an index. asset classes, and be nimble as market conditions change. We encourage you to talk with your financial advisor and visit blackrock.com for further insight about investing in today’s markets. Sincerely, Rob Kapito