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Portfolio – Summary Emerging Markets Equity Portfolio – Summary Research International Core Portfolio – Summary Growth Stock Portfolio – Summary Equity Income Portfolio – Summary Short-Term Bond Portfolio – Summary Large Company Value Portfolio – Summary Asset Allocation Portfolio – Summary 2024-04-30 NORTHWESTERN MUTUAL SERIES FUND INC 0000742212 false 2024-04-30 2024-04-30 N-1A 497 0.0690 0.1720 0.0314 -0.0220 0.0468 0.0358 -0.0261 0.0902 0.0957 0.0661 -0.1296 0.0390 0.1669 -0.0133 0.2323 0.1181 -0.1285 0.2921 0.0167 0.2327 -0.0115 0.0626 -0.0452 -0.0173 -0.0341 0.3003 -0.1128 0.3480 0.1791 0.1592 -0.2313 0.2077 0.1387 -0.0009 0.1498 0.1378 -0.0281 0.2077 0.0073 0.2271 -0.0299 0.0371 0.0325 -0.0222 0.1109 0.0838 -0.0130 0.1404 0.0613 -0.0008 -0.1539 0.0971 -0.0880 -0.0221 0.0289 0.2230 -0.1541 0.1260 -0.0271 0.0500 -0.0683 0.1609 0.0942 -0.0238 0.2038 0.1596 -0.1133 0.2588 0.1337 0.2446 -0.1326 0.1615 0.0849 0.0071 0.0083 0.2029 -0.0738 0.3301 0.2541 0.1018 -0.2377 0.1496 0.1346 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Current income is a secondary objective. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0042 0 0.0001 0.0043 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 44 138 241 542 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 9.33% of the average value of its portfolio. 0.0933 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in the equity securities of medium and large capitalization companies. For this purpose, medium and large capitalization companies are those with a market capitalization of companies in the Russell 1000® Growth Index. As of March 31, 2024, companies in the Russell 1000® Growth Index had market capitalizations between approximately $799.90 million and $3.13 trillion.The Portfolio invests in “blue chip” growth companies, which are companies that, in the adviser’s view, are well established in their industries and have the potential for above-average earnings growth. The adviser looks for companies with leading market positions, seasoned management, and strong financial fundamentals. The Portfolio’s investment approach reflects the adviser’s belief that solid company fundamentals (with an emphasis on the potential for strong growth in earnings per share or operating cash flow) combined with a positive outlook for a company’s industry will ultimately reward investors with strong investment performance. The adviser may look for companies with good prospects for dividend growth. While the Portfolio does not seek to focus its investments in any particular sector, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector as a result of the adviser’s stock selection process. The adviser integrates environmental, social, and governance (ESG) factors into its investment research process for certain investments. While ESG matters vary widely, the adviser generally considers ESG factors such as climate change, resource depletion, labor standards, diversity, human rights issues, and governance structure and practices. For certain types of investments, including, but not limited to, cash, currency positions, and particular types of derivatives, an ESG analysis may not be relevant or possible due to lack of data. Where ESG considerations are integrated into the investment research process, the adviser focuses on the ESG factors that it considers most likely to have a material impact on the performance of the holdings in the Portfolio. The adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio.In pursuing its investment objective, the Portfolio has the discretion to deviate from its normal investment criteria. These situations might arise when the adviser believes a security could increase in value for a variety of reasons, including an extraordinary corporate event, a new product introduction or innovation, a favorable competitive development, or a change in management.The Portfolio invests primarily in common stocks. In keeping with the Portfolio’s investment objective, it may also invest up to 20% of net assets in foreign based companies listed on foreign exchanges, either directly or through American Depositary Receipts (ADRs).The Portfolio may sell a security for a variety of reasons, such as a significant adverse change in the company’s business fundamentals, to secure gains or limit losses, or to redeploy assets into more promising opportunities. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Dividend-Paying Stock Risk – The Portfolio’s emphasis on dividend-paying stocks could cause the Portfolio to underperform similar funds that invest without consideration of a company’s track record of paying dividends. Stocks with a history of paying dividends may not participate in a broad market advance to the same degree as most other stocks. Currently, interest rates remain at historically low levels, and a sharp rise in interest rates or economic downturn could cause a company to unexpectedly reduce or eliminate its dividend. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. •Investment Style Risk – A Portfolio managed using a growth style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mid Cap Company Risk – Investing in mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Prior to November 14, 2019, the sub-adviser to the Portfolio was different. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202027.90%Worst Quarter2nd quarter, 2022-25.37% Best Quarter 2020-06-30 0.2790 Worst Quarter 2022-06-30 -0.2537 Average Annual Total Return(for periods ended December 31, 2023) 0.4969 0.1338 0.1082 0.4268 0.1950 0.1486 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0073 0 0.0001 0.0074 -0.0012 0.0062 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 63 225 400 907 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 6.9% of the average value of its portfolio. PRINCIPAL INVESTMENT STRATEGIES The Portfolio invests primarily in the equity securities of companies selected for their growth potential. The Portfolio focuses on equity securities of large capitalization companies, but may invest in companies of any size. For this purpose, large capitalization companies are those with a market capitalization in excess of $5 billion at the time of purchase.The adviser employs a growth style of equity management that emphasizes companies with sustainable competitive advantages versus others, long-term structural growth drivers that will lead to above-average future cash flow growth, attractive cash flow returns or invested capital, and management teams focused on creating long-term value for shareholders. Long-term structural growth drivers are dynamics that in the manager’s opinion are not likely to change for five years or longer such as the transition of consumer shopping from in-store to online. The adviser aims to invest in companies when they trade at a significant discount to the estimate of their intrinsic value. The intrinsic value of a company is the true worth of its business as perceived by the portfolio managers, which may not be fully reflected in the market price of its stock. The adviser calculates the intrinsic value of a company by the discounted net present value of future cash flows. The Portfolio normally invests across a wide range of sectors and industries. The Portfolio’s sector exposure relative to its benchmark is driven by the adviser’s stock selection process and, as a result, may at times have a relatively high percentage of its assets invested in a particular sector.The Portfolio invests primarily in a core group of 30-40 securities, but may exceed this range. The Portfolio invests primarily in common stocks. The Portfolio may invest up to 20% of its net assets in foreign securities, including American Depositary Receipts (ADRs) and emerging market securities. The Portfolio may also invest in real estate investment trusts (REITs). The Portfolio is classified as “non-diversified” under the Investment Company Act of 1940, as amended, which means it may hold a larger position in a particular company or smaller number of companies than a “diversified” fund.The Portfolio may sell an investment when the portfolio manager believes an unfavorable structural change occurs within a given business or the markets in which it operates, a critical underlying investment assumption is flawed, when a more attractive reward-to-risk opportunity becomes available, when the current price reflects intrinsic value, or for other investment reasons which the portfolio manager deems appropriate. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Investment Style Risk – A Portfolio managed using a growth style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Liquidity Risk – Certain of the Portfolio’s investments, such as small cap stocks and foreign securities, in particular emerging market securities, may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mid and Small Cap Company Risk – Investing in mid and small cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Non-Diversification Risk – The Portfolio is classified as a non-diversified fund and is permitted to invest a greater portion of its assets in a single security or a small number of securities. As a result, an increase or decrease in the value of single security held by the Portfolio may have a greater impact on the Portfolio’s net asset value and total return, and the Portfolio’s performance could be more volatile than the performance of funds that hold a greater number of securities. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202024.14%Worst Quarter2nd quarter, 2022-22.74% Best Quarter 2020-06-30 0.2414 Worst Quarter 2022-06-30 -0.2274 Average Annual Total Return(for periods ended December 31, 2023) 0.5099 0.1778 0.1456 0.4268 0.1950 0.1486 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital and income. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0042 0 0.0003 0.0045 -0.0001 0.0044 Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 45 143 251 566 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 63.49% of the average value of its portfolio. 0.6349 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in equity securities of large capitalization companies. For this purpose, large capitalization equity investments are those whose market capitalizations are above $5 billion at the time of purchase.In managing the Portfolio, the adviser allocates the Portfolio’s assets across a variety of industries, selecting companies in each industry based on the research of a team of global industry analysts. The Portfolio typically seeks to maintain representation in each major industry represented by broad-based, large cap U.S. equity indices.In analyzing a prospective investment for the Portfolio, the adviser utilizes a “bottom-up” approach, which is the use of fundamental analysis to identify specific securities for purchase or sale. Fundamental analysis of a company involves the assessment of a variety of factors, including the company’s business environment, management quality, balance sheet, income statement, anticipated earnings, revenues and dividends, and other related measures or indicators of valuation and growth potential. The adviser also integrates the evaluation of financially material environmental, social, and/or governance (ESG) characteristics (where available for a company) into its fundamental analysis. Examples of ESG factors that may be considered include, but are not limited to, employee engagement, talent attraction and retention, incentive structures, and corporate strategy. Consideration of ESG factors may not be determinative in the adviser’s investment process and the adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio. The Portfolio’s sector exposures generally conform with the sector weights present in the Portfolio’s benchmark index and as a result, in combination with the Portfolio’s reliance on fundamental company analysis, and based upon market or economic conditions, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector of the market.The Portfolio invests primarily in U.S. common stocks. Up to 20% of the Portfolio’s net assets may be invested in foreign based companies listed on foreign exchanges, either directly or through American Depositary Receipts (ADRs). The Portfolio may also invest in real estate investment trusts (REITs).The Portfolio may sell a security for a variety of reasons, including a significant adverse change in the company’s business fundamentals, if the company has become significantly overvalued in terms of earnings, assets or growth prospects, or more attractive alternatives exist. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. •Investment Style Risk – A portfolio managed using a particular style of investing, such as growth or value or a combination of both, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Prior to October 27, 2017, the sub-adviser to the Portfolio was different. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202021.81%Worst Quarter1st quarter, 2020-18.72% Best Quarter 2020-06-30 0.2181 Worst Quarter 2020-03-31 -0.1872 Average Annual Total Return(for periods ended December 31, 2023) 0.2578 0.1550 0.1057 0.2629 0.1570 0.1203 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to seek long-term growth of capital and income. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0076 0 0.0006 0.0082 -0.0012 0.0070 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 72 250 443 1002 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 118.92% of the average value of its portfolio. 1.1892 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of its net assets (plus any borrowings for investment purposes), in equity securities of large-capitalization U.S. companies listed or traded on U.S. securities exchanges. The Portfolio defines large capitalization companies as those with a market capitalization in excess of $5 billion, at the time of investment. The Portfolio invests primarily in equity securities of U.S. companies. The Portfolio may also invest up to 20% of its net assets in common stocks of foreign issuers, and may hold American Depositary Receipts (ADRs). The Portfolio may also invest in real estate investment trusts (REITs).The Portfolio focuses on those equity securities that it considers attractively valued and seeks to outperform the benchmark through superior stock selection. By emphasizing attractively valued equity securities, the Portfolio seeks to produce returns that exceed those of the benchmark.In managing the Portfolio, the Adviser employs a three-step process that combines research, valuation and stock selection. The Adviser takes an in-depth look at company prospects, which is designed to provide insight into a company’s real growth potential. The research findings allow the Adviser to rank the companies in each sector according to their relative value (i.e., ranking companies from most- to least-undervalued in the Adviser’s assessment). As part of its investment process, the Adviser seeks to assess the impact of environmental, social and governance (ESG) factors on many issuers in the universe in which the Portfolio invests. The Adviser’s assessment is based on an analysis of key opportunities and risks across industries to seek to identify financially material issues with respect to the Portfolio’s investments in securities and ascertain key issues that merit engagement with issuers. These ESG factor assessments may not be conclusive and securities of issuers may be purchased and retained by the Portfolio for reasons other than material ESG factors while the Portfolio may divest or not invest in securities of issuers that may be positively impacted by such factors. Examples of ESG factors which may be considered (which are provided for illustrative purposes only, are not exhaustive and may not be relevant to a particular investment) are climate change risk, human capital management and executive compensation. The Adviser’s ESG integration approach does not change the Portfolio’s investment objective, exclude specific types of industries or companies or limit the Portfolio’s investable universe. The Portfolio is not designed for investors who wish to screen out particular types of companies or investments or are looking for funds that meet specific ESG goals. On behalf of the Portfolio, the Adviser then buys and sells equity securities, using the research and valuation rankings as a basis. In general, the Adviser buys equity securities that are identified as attractively valued and considers selling them when they appear to be overvalued. Along with attractive valuation, the adviser often considers a number of other criteria:•catalysts that could trigger a rise in a stock’s price•high potential reward compared to potential risk•temporary mispricing caused by apparent market overreactions PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. •Investment Style Risk – A portfolio managed using a particular style of investing, such as growth or value or a combination of both, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mid Cap Company Risk – Investing in mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Prior to July 31, 2023, the Portfolio was managed by a different sub-adviser. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202015.58%Worst Quarter1st quarter, 2020-23.32% Best Quarter 2020-12-31 0.1558 Worst Quarter 2020-03-31 -0.2332 Average Annual Total Return(for periods ended December 31, 2023) 0.2061 0.1094 0.0917 0.2629 0.1570 0.1203 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to achieve investment results that approximate the performance of the Standard & Poor’s 500 Composite Stock Price Index (“S&P 500® Index”). FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0020 0 0.0001 0.0021 -0.0001 0.0020 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 20 67 117 267 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 2.16% of the average value of its portfolio. 0.0216 PRINCIPAL INVESTMENT STRATEGIES The Portfolio employs a “passive management,” or indexing, investment approach designed to track the performance of the S&P 500® Index. The S&P 500® Index is composed of the stocks of primarily large capitalization companies that represent a broad spectrum of the U.S. economy and a substantial part of the U.S. stock market’s total capitalization. As of March 31, 2024, the market capitalization range of the S&P 500® Index was approximately $5.96 billion to $3.13 trillion. The Portfolio attempts to achieve its objective by investing all, or substantially all, of its assets in the stocks that make up the S&P 500® Index, holding each stock in approximately the same proportion as its weighting in the Index. This is known as a full replication strategy. The Portfolio may also invest in equity index futures and exchange traded funds for cash management and liquidity purposes and to help achieve full replication.Standard & Poor’s constructs the Index by first identifying major industry categories and then allocating a representative sample of the larger and more liquid stocks in those industries to the index. S&P weights each stock according to its float-adjusted market value. For example, the 50 largest companies in the index may account for over 50% of its value.Because the Portfolio is managed with a goal of fully replicating the underlying S&P 500® Index, the approach employed by the Portfolio with respect to reconstitution and rebalancing aligns with the process followed generally by the S&P 500® Index. Changes to the underlying company constituents of the S&P 500® Index are made on an as-needed basis and are usually announced several days before they are scheduled to be implemented. The S&P 500® Index typically makes weightings adjustments based on changes in the amount of a constituent company’s shares outstanding on a quarterly basis. The constituent and share-based weightings changes made by the S&P 500® Index will be made in a parallel fashion by the Portfolio on substantially the same timeline. Additionally, the Portfolio utilizes cash equitization instruments, and rebalancing occurs as necessary to maintain balances within established target ranges for these instruments. Cash equitization as employed by the Portfolio is a strategy pursuant to which the Portfolio will acquire certain derivative instruments, such as equity index futures, whereby the futures will be utilized to replicate index returns and enable the Portfolio to be fully invested, while still maintaining cash balances as needed by the Portfolio. This strategy works to limit the extent to which uninvested cash will weigh negatively on overall Portfolio returns when markets go up.The Index 500 Stock Portfolio’s ability to match the performance of the S&P 500® Index will be affected to some extent by the size and timing of cash flows into and out of the Index 500 Stock Portfolio. The Portfolio will be managed with a view to reducing such effects. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index and the risk of adverse price movements in the market. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include counterparty and liquidity risks. The Portfolio’s purchase of futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. •Equity Securities Risk – The value of equity securities, such as the stocks in which the Portfolio invests, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Exchange Traded Funds Risk – Investing in exchange traded funds (ETFs) may expose the Portfolio to greater risk of loss and price fluctuation than investing directly in a comparable portfolio of stocks comprising the index due to lack of liquidity, the additional expenses incurred as a shareholder in another investment company, and tracking error. ETFs are also subject to the risk that their market prices may trade at a premium or discount to their net asset value, which means the Portfolio will overpay for an ETF’s assets if it is trading at a premium and will get less than the value of the ETF’s assets when selling if it is trading at a discount. An active market for an ETF may not be developed or maintained. Trading of an ETF’s shares may be halted by the exchange, in which case the Portfolio would be unable to sell its ETF shares unless and until trading is resumed. •Indexing Strategy Risk –A Portfolio using a passive management strategy is not “actively” managed, and therefore does not engage in shifting portfolio assets to take advantage of market opportunity, and does not attempt to manage market volatility, use defensive strategies or reduce the effects of any long-term periods of poor stock performance. Since the Portfolio implements a full replication strategy with respect to the index which it tracks, to the extent the index has a significant allocation to an industry or group of industries, a particular sector, or to a single issuer or small number of issuers, the Portfolio will exhibit a significant investment level in that industry, group of industries, sector, issuer or small number of issuers. Portfolio performance may be adversely affected by a significant investment in an industry, group of industries, sector, issuer or small number of issuers, and may be more susceptible to adverse economic, market, political or regulatory developments affecting the industry, group of industries sector or issuer(s) subject to a significant level of investment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Tracking Error Risk – The Portfolio may be subject to tracking error, which is the divergence of the Portfolio’s performance from that of the underlying index. Tracking error may occur due to a number of factors, including differences between the securities held in the Portfolio and those included in the underlying index, and based upon the fact that the Portfolio incurs fees and expenses, while the underlying index does not. Tracking error risk may be heightened during times of increased market volatility or other unusual market conditions. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Prior to February 1, 2021, the Portfolio was managed by Mason Street Advisors, LLC. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202020.47%Worst Quarter1st quarter, 2020-19.62% Best Quarter 2020-06-30 0.2047 Worst Quarter 2020-03-31 -0.1962 Average Annual Total Return(for periods ended December 31, 2023) 0.2604 0.1545 0.1180 0.2629 0.1570 0.1203 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to seek long-term capital growth. Income is a secondary objective. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0070 0 0.0010 0.0080 -0.0005 0.0075 Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 77 250 439 985 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 35.98% of the average value of its portfolio. 0.3598 PRINCIPAL INVESTMENT STRATEGIES The Portfolio invests primarily in larger companies. Accordingly, the Portfolio will normally have at least 80% of its net assets (plus any borrowings for investment purposes) in equity securities of companies comprising the Russell 1000® Index. As of March 31, 2024, the market capitalization range of the Russell 1000® Index was approximately $351.89 million to $3.13 trillion.The adviser looks for stocks of companies that it believes are undervalued at the time of purchase. The adviser uses a value investment strategy that looks for companies that are temporarily out of favor in the market. The adviser attempts to purchase the stocks of these undervalued companies and hold each stock until it has returned to favor in the market and the price has increased to, or is higher than, a level the adviser believes more accurately reflects the fair value of the company. The Portfolio’s sector exposure relative to its benchmark is driven by the adviser’s stock selection process, and, as a result, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector.Companies may be undervalued due to market declines, poor economic conditions, actual or anticipated bad news regarding the issuer or its industry, or because they have been overlooked by the market. To identify these companies, the adviser looks for companies with earnings, cash flows and/or assets that may not be reflected accurately in the companies’ stock prices. The adviser also may consider whether the companies’ securities have a favorable dividend-paying history and whether dividend payments are expected to continue or increase. The adviser uses a variety of analytical research tools and techniques to help make decisions about buying or holding securities of companies that meet its investment criteria and sell the securities of companies that do not. In addition to fundamental financial metrics, the adviser may also consider environmental, social and/or governance (ESG) data. However, the adviser may not consider ESG data with respect to every investment decision and, even when such data is considered, they may conclude that other attributes of an investment outweigh ESG considerations when making decisions for the Portfolio. Examples of ESG data considered may include, but are not limited to, carbon emissions, waste and harmful substance management, product and employee safety, human capital management, and corporate governance structure and oversight.While most assets will be invested in U.S. equity securities, which includes common stocks, preferred stocks, warrants and securities convertible into common or preferred stocks, in keeping with the Portfolio’s objectives, it may also invest in American Depositary Receipts (ADRs) and foreign securities (up to 20% of net assets), including those of companies located in emerging markets. The Portfolio may utilize futures for cash management purposes and forwards to hedge foreign currency exposure.The adviser may sell stocks from the Portfolio if it believes a stock no longer meets established valuation criteria. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Convertible Securities Risk – Convertible securities (which can be bonds, notes, debentures, preferred stock, or other securities which are convertible into or exercisable for common stock), are subject to both the credit and interest rate risks associated with fixed income securities and to the stock market risk associated with equity securities. The value of a convertible security may not increase or decrease as rapidly as the underlying common stock. The Portfolio may be forced to convert a security before it would otherwise choose, which may have an adverse effect on the Portfolio’s ability to achieve its investment objective. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that the counterparty to a derivatives transaction fails to make the required payment or otherwise comply with the terms of the contract, the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index, the risk of adverse price movements in the market, and the risk of missed opportunities in other investments. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include management, interest rate, and liquidity risks. The Portfolio’s purchase of forwards and futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. In addition, the purchase of forwards also involves counterparty credit risk as well as heightened market risk. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common and preferred stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Investment Style Risk – A portfolio managed using a value style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Preferred Stocks Risk – Preferred stocks often lack a fixed maturity or redemption date and are therefore more susceptible to price fluctuations when interest rates change. They also carry a greater risk of non-receipt of income because unlike interest on debt securities, dividends on preferred stocks must be declared by the issuer’s board of directors before becoming payable. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •Warrants Investing Risk – Investments in warrants may be more volatile than the underlying common stock and may cause the Portfolio increased risk of loss if the warrants cannot be exercised prudently by the expiration date or if the warrants lack a liquid secondary market for resale. Warrants can provide exposure to an underlying stock for a portion of the price of direct ownership of shares of that stock. As a result, most warrants have some degree of leverage, which can vary depending on the type of warrant. This means that small changes in the value of the underlying stock results in larger changes in the value of the warrant. This can magnify gains when stock prices rise, but it can also magnify losses when stock prices fall. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202214.66%Worst Quarter1st quarter, 2020-25.07% Best Quarter 2022-12-31 0.1466 Worst Quarter 2020-03-31 -0.2507 Average Annual Total Return(for periods ended December 31, 2023) 0.0380 0.1057 0.0780 0.1146 0.1091 0.0840 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital and income. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0052 0 0.0002 0.0054 -0.0004 0.0050 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 51 169 298 673 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 22.58% of the average value of its portfolio. 0.2258 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in equity securities of U.S. issuers. Generally, the companies in which the Portfolio invests will have a market value of $5 billion or more. The Portfolio employs a focused investment strategy and typically invests in a core group of 30-40 securities.The Portfolio primarily invests in common stocks of large-capitalization companies, but may also invest in mid-capitalization companies, that its adviser believes have long-term capital appreciation potential. Typically, the Portfolio seeks securities the adviser believes are undervalued in relation to their intrinsic value. The intrinsic value of a company is the true worth of the business, which may not be fully reflected in the market price of its stock. The adviser seeks to determine a company’s intrinsic value as indicated by multiple factors, including the earnings and cash flow potential or the asset valuation of the respective issuers. On a selective basis, the adviser considers a company’s plans for future operation. The Portfolio’s sector exposure relative to its benchmark is driven by the adviser’s stock selection process, and, as a result, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector.The Portfolio may sell a security if it no longer believes the security will contribute to meeting the investment objective of the Portfolio. In considering whether to sell a security, the Portfolio may evaluate, among other things, the factors listed above, the condition of the U.S. economy, the condition of non-U.S. economies, and changes in the condition and outlook in the issuer’s industry or sector. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Investment Style Risk – A portfolio managed using a value style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mid Cap Company Risk – Investing in mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Security Focus Risk – The Portfolio’s performance could be more closely tied to the value of a single security or small number of securities because, although classified as a diversified investment company, the Portfolio may hold large positions in a single or small number of securities. As a result, the Portfolio’s performance could be more volatile than the performance of funds that hold a greater number of securities. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202015.36%Worst Quarter1st quarter, 2020-26.34% Best Quarter 2020-06-30 0.1536 Worst Quarter 2020-03-31 -0.2634 Average Annual Total Return(for periods ended December 31, 2023) 0.0371 0.0848 0.0807 0.1146 0.1091 0.0840 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital and income. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0064 0 0.0002 0.0066 -0.0009 0.0057 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 58 202 359 814 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 18.25% of the average value of its portfolio. 0.1825 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in common stocks, with an emphasis on larger capitalization stocks with a strong track record of paying dividends or that are believed to be undervalued. For this purpose, larger capitalization stocks are those with a market capitalization greater than $5 billion. The Portfolio generally seeks investments in large-capitalization companies and the Portfolio’s yield, which reflects the level of dividends paid by the Portfolio, is expected to normally exceed the yield of the Russell 1000® Value Index. This level is merely a guideline and there can be no certainty this level will be achieved.The Portfolio will typically employ a value approach in selecting investments. The adviser’s in-house research team seeks to identify companies that appear to be undervalued as measured by price to earnings ratio, dividend yield, enterprise value to sales, among other metrics and may be temporarily out of favor, but have good prospects for capital appreciation and dividend growth. While the Portfolio does not seek to focus its investments in any particular economic sector, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector as a result of the adviser’s stock selection process. The adviser integrates environmental, social, and governance (ESG) factors into its investment research process for certain investments. While ESG matters vary widely, the adviser generally considers ESG factors such as climate change, resource depletion, labor standards, diversity, human rights issues, and governance structure and practices. For certain types of investments, including, but not limited to, cash, currency positions, and particular types of derivatives, an ESG analysis may not be relevant or possible due to lack of data. Where ESG considerations are integrated into the investment research process, the adviser focuses on the ESG factors that it considers most likely to have a material impact on the performance of the holdings in the Portfolio. The adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio.The adviser has the discretion to deviate from the Portfolio’s normal investment criteria, as described above, and purchase securities the adviser believes could provide an opportunity for substantial appreciation. These special situations might arise when the adviser believes a security could increase in value for a variety of reasons, including a change in management, a reorganization, a spin-off of a business line, a special dividend, or some other extraordinary corporate event, a new product introduction or a favorable competitive development.While most assets will be invested in U.S. common stocks, the Portfolio may also invest in foreign securities and American Depositary Receipts (ADRs) (up to 20% of net assets), including those of issuers located in emerging markets. The Portfolio may also invest in real estate investment trusts (REITs).The Portfolio may sell securities for a variety of reasons such as to secure gains, limit losses, or redeploy assets into more promising opportunities. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Dividend-Paying Stock Risk – The Portfolio’s emphasis on dividend-paying stocks could cause the Portfolio to underperform similar funds that invest without consideration of a company’s track record of paying dividends. Stocks with a history of paying dividends may not participate in a broad market advance to the same degree as most other stocks. Currently, interest rates remain at historically low levels, and a sharp rise in interest rates or economic downturn could cause a company to unexpectedly reduce or eliminate its dividend. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common and preferred stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Investment Style Risk – A portfolio managed using a value style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Special Situation Risk – In special situations, the adviser may deviate from the Portfolio’s normal investment criteria when purchasing a security. In these special situations, there is the risk that the change or event anticipated by the adviser when purchasing a company might not occur or attract the expected attention, which could have a negative impact on the price of the issuer's securities. Investing in special situations may involve heightened volatility in the value of the securities purchased and may cause greater risk of loss. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202020.93%Worst Quarter1st quarter, 2020-28.46% Best Quarter 2020-12-31 0.2093 Worst Quarter 2020-03-31 -0.2846 Average Annual Total Return(for periods ended December 31, 2023) 0.0968 0.1132 0.0796 0.1146 0.1091 0.0840 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0052 0 0.0002 0.0054 0.0000 0.0054 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 55 173 302 677 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 39.37% of the average value of its portfolio. 0.3937 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in stocks of mid-sized companies. The Portfolio considers a company to be a mid-capitalization company if it has a market capitalization within the collective range of the Russell MidCap® Index and the S&P MidCap 400® Index. As of March 31, 2024, this range was approximately $351.89 million to $89.01 billion. The market capitalization range of these indices changes over time. Securities of companies whose market capitalizations no longer fall within this collective range after purchase may continue to be held by the Portfolio.The Portfolio invests primarily in common stocks of mid cap companies selected on the basis of their potential for capital appreciation. The Portfolio focuses on companies that are determined to be of high quality. The key characteristics of high quality companies include a leadership position within an industry, a strong balance sheet, a high return on equity, and/or a strong management team. The adviser uses fundamental analysis to evaluate a security for purchase or sale by the Portfolio. Fundamental analysis of a company involves the assessment of such factors as its business environment, management quality, balance sheet, income statement, anticipated earnings, revenues and dividends, and environmental, social, and/or governance (ESG) characteristics. Examples of ESG factors that may be considered include, but are not limited to, employee engagement, talent attraction and retention, incentive structures, and corporate strategy. Consideration of ESG factors may not be determinative in the adviser’s investment process and the adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio.The Portfolio seeks to reduce overall risk by diversifying across sectors, industry groups and companies. The Portfolio’s sector exposure relative to its benchmark is driven by an investment process which relies on fundamental company analysis and individual stock selection. As a result, based upon market or economic conditions, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector of the market.The Portfolio invests primarily in U.S. common stocks. The Portfolio may also invest up to 20% of net assets in American Depositary Receipts (ADRs) and other securities of foreign issuers, including non-U.S. dollar denominated securities. The Portfolio may invest in real estate investment trusts (REITs).The Portfolio typically trims positions as valuation appears incrementally less attractive, and may sell a stock when the adviser’s investment thesis is no longer valid, typically due to an erosion of company fundamentals relative to expectations or when valuation is no longer attractive. The Portfolio may, but is not required to, exit a position if the company’s capitalization grows beyond the mid cap range. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Currency Risk – The risk that foreign (non-U.S. dollar) currency denominated securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar. Investments in securities subject to foreign currency risk may have more rapid and extreme changes in value or more losses than investments in U.S. dollar denominated securities. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. •Investment Style Risk – A portfolio managed using a growth style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mid Cap Company Risk – Investing in mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Prior to October 27, 2017, the sub-adviser to the Portfolio was different. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202026.37%Worst Quarter1st quarter, 2020-24.21% Best Quarter 2020-12-31 0.2637 Worst Quarter 2020-03-31 -0.2421 Average Annual Total Return(for periods ended December 31, 2023) 0.1496 0.1000 0.0705 0.2587 0.1381 0.1057 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to achieve investment results that approximate the performance of the S&P MidCap 400® Stock Price Index (“S&P MidCap 400® Index”). FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0025 0 0.0003 0.0028 -0.0003 0.0025 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 26 87 154 353 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 19.05% of the average value of its portfolio. 0.1905 PRINCIPAL INVESTMENT STRATEGIES The Portfolio employs a “passive management,” or indexing, investment approach designed to track the performance of the S&P MidCap 400® Index. The S&P MidCap 400® Index is composed of the stocks of companies whose capitalizations generally are smaller than those of companies that comprise the S&P 500® Index. The S&P MidCap 400® Index does not include the stocks of the very large companies that account for most of the weighting in the S&P 500® Index. As of March 31, 2024, the market capitalization range of the S&P MidCap 400® Index was approximately $2.19 billion to $47.33 billion. The Portfolio attempts to achieve its objective by investing all, or substantially all, of its assets in the stocks that make up the S&P MidCap 400® Index, holding each stock in approximately the same proportion as its weighting in the Index. This is known as a full replication strategy. The Portfolio may also invest in equity index futures and exchange traded funds for cash management and liquidity purposes and to help achieve full replication.Standard & Poor’s constructs the index by first identifying major industry categories and then allocating a representative sample of the larger and more liquid stocks in those industries to the index. S&P weights each stock according to its float-adjusted market value. For example, the 50 largest companies in the index may account for over 50% of its value.Because the Portfolio is managed with a goal of fully replicating the underlying S&P MidCap 400® Index, the approach employed by the Portfolio with respect to reconstitution and rebalancing aligns with the process followed generally by the S&P MidCap 400®Index. Changes to the underlying company constituents of the S&P MidCap 400® Index are made on an as-needed basis and are usually announced several days before they are scheduled to be implemented. The S&P MidCap 400® Index typically makes weightings adjustments based on changes in the amount of a constituent company’s shares outstanding on a quarterly basis. The constituent and share-based weightings changes made by S&P MidCap 400® Index will be made in a parallel fashion by the Portfolio on substantially the same timeline. Additionally, the Portfolio utilizes cash equitization instruments, and rebalancing occurs as necessary to maintain balances within established target ranges for these instruments. Cash equitization as employed by the Portfolio is a strategy pursuant to which the Portfolio will acquire certain derivative instruments, such as equity index futures, whereby the futures will be utilized to replicate index returns and enable the Portfolio to be fully invested, while still maintaining cash balances as needed by the Portfolio. This strategy works to limit the extent to which uninvested cash will weigh negatively on overall Portfolio returns when markets go up.The Index 400 Stock Portfolio’s ability to match the performance of the S&P MidCap 400® Index will be affected to some extent by the size and timing of cash flows into and out of the Index 400 Stock Portfolio. The Portfolio will be managed with a view to reducing such effects. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index and the risk of adverse price movements in the market. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include counterparty and liquidity risks. The Portfolio’s purchase of futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. •Equity Securities Risk – The value of equity securities, such as the stocks in which the Portfolio invests, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Exchange Traded Funds Risk – Investing in exchange traded funds (ETFs) may expose the Portfolio to greater risk of loss and price fluctuation than investing directly in a comparable portfolio of stocks comprising the index due to lack of liquidity, the additional expenses incurred as a shareholder in another investment company, and tracking error. ETFs are also subject to the risk that their market prices may trade at a premium or discount to their net asset value, which means the Portfolio will overpay for an ETF’s assets if it is trading at a premium and will get less than the value of the ETF’s assets when selling if it is trading at a discount. An active market for an ETF may not be developed or maintained. Trading of an ETF’s shares may be halted by the exchange, in which case the Portfolio would be unable to sell its ETF shares unless and until trading is resumed. •Indexing Strategy Risk –A Portfolio using a passive management strategy is not “actively” managed, and therefore does not engage in shifting portfolio assets to take advantage of market opportunity, and does not attempt to manage market volatility, use defensive strategies or reduce the effects of any long-term periods of poor stock performance. Since the Portfolio implements a full replication strategy with respect to the index which it tracks, to the extent the index has a significant allocation to an industry or group of industries, a particular sector, or to a single issuer or small number of issuers, the Portfolio will exhibit a significant investment level in that industry, group of industries, sector, issuer or small number of issuers. Portfolio performance may be adversely affected by a significant investment in an industry, group of industries, sector, issuer or small number of issuers, and may be more susceptible to adverse economic, market, political or regulatory developments affecting the industry, group of industries sector or issuer(s) subject to a significant level of investment. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mid Cap Company Risk – Investing in mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Tracking Error Risk – The Portfolio may be subject to tracking error, which is the divergence of the Portfolio’s performance from that of the underlying index. Tracking error may occur due to a number of factors, including differences between the securities held in the Portfolio and those included in the underlying index, and based upon the fact that the Portfolio incurs fees and expenses, while the underlying index does not. Tracking error risk may be heightened during times of increased market volatility or other unusual market conditions. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Prior to February 1, 2021, the Portfolio was managed by Mason Street Advisors, LLC. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202024.28%Worst Quarter1st quarter, 2020-29.68% Best Quarter 2020-12-31 0.2428 Worst Quarter 2020-03-31 -0.2968 Average Annual Total Return(for periods ended December 31, 2023) 0.1615 0.1234 0.0899 0.1644 0.1263 0.0927 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term capital growth. Current income is a secondary objective. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0085 0 0.0003 0.0088 -0.0016 0.0072 Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 74 265 472 1070 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 50.26% of the average value of its portfolio. 0.5026 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in equity securities of mid-sized companies. The Portfolio invests primarily in a diversified portfolio of equity securities of mid-sized companies that are determined by Portfolio’s adviser to be undervalued at the time of purchase. At the time of investment, companies purchased typically will fall within the capitalization range of the Russell 3000® Index, excluding the largest 100 such companies, (approximately $16.55 million to $94.47 billion as of March 31, 2024). The adviser intends to manage the Portfolio so that its weighted capitalization falls within the capitalization range of the members of the Russell MidCap® Index (approximately $351.89 million to $89.01 billion as of March 31, 2024).In managing the Portfolio, the adviser uses its own fundamental value approach. In selecting securities for the Portfolio, the adviser attempts to identify companies whose long-term earnings, cash flows and/or assets are not reflected in the current market price of their securities and hold each security until it has returned to favor in the market and the price has increased to, or is higher than a level the adviser believes more accurately reflects the fair value of the company. The adviser may also consider whether the companies’ securities have a favorable dividend-paying history and whether dividend payments are expected to continue or increase. The adviser uses a variety of analytical research tools and techniques to help make decisions about buying or holding securities of companies that meet its investment criteria and sell the securities of companies that do not. In addition to fundamental financial metrics, the adviser may also consider environmental, social and/or governance (ESG) data. However, the adviser may not consider ESG data with respect to every investment decision and, even when such data is considered, they may conclude that other attributes of an investment outweigh ESG considerations when making decisions for the Portfolio. Examples of ESG data considered may include, but are not limited to, carbon emissions, waste and harmful substance management, product and employee safety, human capital management, and corporate governance structure and oversight. The Portfolio’s sector exposure relative to its benchmark is driven by the adviser’s stock selection process, and, as a result, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector.While most assets will be invested in U.S. equity securities, which includes common stocks, preferred stocks, warrants and securities convertible into common or preferred stocks, in keeping with the Portfolio’s objectives, it may also invest in American Depositary Receipts (ADRs) and foreign securities (up to 20% of net assets), including those of companies located in emerging markets. The Portfolio may also invest in real estate investment trusts (REITs). The Portfolio may utilize futures for cash management purposes and forwards to hedge foreign currency exposure.The adviser may sell a stock from the Portfolio if it believes the stock no longer meets established valuation criteria, the stock’s risk parameters outweigh its return opportunity, specific events alter a stock’s prospects or more attractive opportunities are identified. In seeking to achieve its investment objective, the adviser may sell shares from the Portfolio without regard to the length of time a security has been held. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Convertible Securities Risk – Convertible securities (which can be bonds, notes, debentures, preferred stock, or other securities which are convertible into or exercisable for common stock), are subject to both the credit and interest rate risks associated with fixed income securities and to the stock market risk associated with equity securities. The value of a convertible security may not increase or decrease as rapidly as the underlying common stock. The Portfolio may be forced to convert a security before it would otherwise choose, which may have an adverse effect on the Portfolio’s ability to achieve its investment objective. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that the counterparty to a derivatives transaction fails to make the required payment or otherwise comply with the terms of the contract, the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index, and the risk of missed opportunities in other investments. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include management, market, interest rate, and liquidity risks. The Portfolio’s purchase of forwards and futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. In addition, the purchase of forwards also involves counterparty credit risk as well as heightened market risk. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common and preferred stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Investment Style Risk – A portfolio managed using a value style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mid Cap Company Risk – Investing in mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Preferred Stocks Risk – Preferred stocks often lack a fixed maturity or redemption date and are therefore more susceptible to price fluctuations when interest rates change. They also carry a greater risk of non-receipt of income because unlike interest on debt securities, dividends on preferred stocks must be declared by the issuer’s board of directors before becoming payable. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •Warrants Investing Risk – Investments in warrants may be more volatile than the underlying common stock and may cause the Portfolio increased risk of loss if the warrants cannot be exercised prudently by the expiration date or if the warrants lack a liquid secondary market for resale. Warrants can provide exposure to an underlying stock for a portion of the price of direct ownership of shares of that stock. As a result, most warrants have some degree of leverage, which can vary depending on the type of warrant. This means that small changes in the value of the underlying stock results in larger changes in the value of the warrant. This can magnify gains when stock prices rise, but it can also magnify losses when stock prices fall. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202016.84%Worst Quarter1st quarter, 2020-27.57% Best Quarter 2020-12-31 0.1684 Worst Quarter 2020-03-31 -0.2757 Average Annual Total Return(for periods ended December 31, 2023) 0.0626 0.1121 0.0893 0.1271 0.1116 0.0826 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0054 0 0.0002 0.0001 0.0057 Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 58 183 318 714 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 63.94% of the average value of its portfolio. 0.6394 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in common stocks of small capitalization companies. The Portfolio defines small capitalization companies as companies with market capitalizations within the collective range of the Russell 2000® and S&P SmallCap 600® Indices. As of March 31, 2024, this range was approximately $16.55 million to $59.14 billion. Some of the companies in which the Portfolio invests may be considered micro cap companies (defined as companies with stock market capitalizations less than $500 million at the time of investment).The Portfolio’s investment process is derived from the observation that the quality and persistence of a company’s business is often not reflected in its current stock price. Central to the investment process is intense, fundamental research focused on uncovering companies with improving quality metrics, business momentum, and attractive relative valuations. The investment process is aided by a proprietary screening process that narrows the investment universe to companies that are consistent with the investment philosophy. The investment team conducts fundamental research on companies elevated by the screening process. Research emphasizes the sustainability of a business’s competitive advantages and the ability to generate revenue and increase profit margins. Other important considerations include capital allocation discipline, and other qualitative factors such as strength of company management, analysis of products and competition, and financially material environmental, social, and/or governance (ESG) characteristics. Examples of ESG factors that may be considered include, but are not limited to, employee engagement, talent attraction and retention, incentive structures, and corporate strategy. Consideration of ESG factors may not be determinative in the adviser’s investment process and the adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio. Valuation analysis is an important component of the investment process and consists of both cash flow and earnings ratios that are compared with the industry average.Portfolio construction emphasizes stock specific risk while minimizing other sources of active risk. The Portfolio is structured so that its sector weights are generally similar to those of the Russell 2000® Growth Index, the Portfolio’s benchmark. As a result, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector and may hold securities which are not represented in the benchmark. However, in constructing the Portfolio, the investment team monitors different sources of active risk including stock-specific risk, industry risk and style risk. The goal of this analysis is to ensure that the Portfolio remains well diversified and does not have unrewarded or unintended industry and style exposure as a consequence of individual stock selections.The Portfolio invests primarily in U.S. common stocks. The Portfolio may also invest up to 20% of net assets in American Depositary Receipts (ADRs) and other equity securities of foreign issuers which are denominated in U.S. dollars. The Portfolio may also invest in real estate investment trusts (REITs).The Portfolio may also utilize exchange-traded funds as part of its cash management strategy.The Portfolio may sell a security for a variety of reasons including when it no longer demonstrates improving quality or exhibits strong fundamental momentum, when fundamentals have changed, where the risk/reward assessment is no longer favorable, or to redeploy assets into more promising opportunities. The Portfolio may, but is not required, to exit a position if the company’s capitalization grows beyond the small cap range. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. The value of securities identified using quantitative analysis can react differently to issuer, political, market and economic developments from the market as a whole or securities identified using only fundamental analysis. The factors used in quantitative analysis and the weight placed on those factors may not be predictive of a security’s value. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Exchange Traded Funds Risk – Investing in exchange traded funds (ETFs) may expose the Portfolio to greater risk of loss and price fluctuation than investing directly in a comparable portfolio of stocks comprising the index due to lack of liquidity, the additional expense incurred as a shareholder in another investment company, and tracking error. ETFs are also subject to the risk that their market prices may trade at a premium or discount to their net asset value, which means the Portfolio will overpay for an ETF’s assets if it is trading at a premium and will get less than the value of the ETF’s assets when selling if it is trading at a discount. An active market for an ETF may not be developed or maintained. Trading of an ETF’s shares may be halted by the exchange, in which case the Portfolio would be unable to sell its ETF shares unless and until trading is resumed. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Investment Style Risk – A portfolio managed using a growth style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Liquidity Risk – Markets for small and micro cap stocks and foreign securities, in particular emerging markets securities, may be less liquid than markets for larger cap stocks and domestic securities, and therefore may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Micro Cap Company Risk – Investing in micro cap stocks may cause the Portfolio to experience more rapid and extreme changes in value than a fund that invests solely in small, mid and large cap stocks due to a more limited track record, narrower product markets, more limited resources, higher risk of failure, and less liquid trading markets. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Small Cap Company Risk – Investing in small cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202031.83%Worst Quarter1st quarter, 2020-26.17% Best Quarter 2020-12-31 0.3183 Worst Quarter 2020-03-31 -0.2617 Average Annual Total Return(for periods ended December 31, 2023) 0.1836 0.0980 0.0768 0.1866 0.0922 0.0716 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to achieve investment results that approximate the performance of the Standard & Poor’s SmallCap 600® Index (“S&P SmallCap 600® Index”). FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0023 0 0.0005 0.0028 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 29 90 157 356 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 24.86% of the average value of its portfolio. 0.2486 PRINCIPAL INVESTMENT STRATEGIES The Portfolio employs a “passive management,” or indexing, investment approach designed to track the performance of the S&P SmallCap 600® Index. S&P SmallCap 600® Index is composed of domestic stocks with market capitalizations ranging between approximately $332.95 million and $7.34 billion as of March 31, 2024. The Portfolio attempts to achieve its objective by investing all, or substantially all, of its assets in stocks that make up the S&P SmallCap 600® Index, holding each stock in approximately the same proportion as its weighting in the Index. This is known as a full replication strategy. The Portfolio may also invest in equity index futures and exchange traded funds for cash management and liquidity purposes and to help achieve full replication.Standard & Poor’s constructs the index by first identifying major industry categories and then allocating a representative sample of the larger and more liquid stocks in those industries to the index. S&P weights each stock according to its float-adjusted market value. For example, the 50 largest companies in the index may account for over 50% of its value.Because the Portfolio is managed with a goal of fully replicating the underlying S&P SmallCap 600® Index, the approach employed by the Portfolio with respect to reconstitution and rebalancing aligns with the process followed generally by the S&P SmallCap 600® Index. Changes to the underlying company constituents of the S&P SmallCap 600® Index are made on an as-needed basis and are usually announced several days before they are scheduled to be implemented. The S&P SmallCap 600® Index typically makes weightings adjustments based on changes in the amount of a constituent company’s shares outstanding on a quarterly basis. The constituent and share-based weightings changes made by S&P SmallCap 600® Index will be made in a parallel fashion by the Portfolio on substantially the same timeline. Additionally, the Portfolio utilizes cash equitization instruments, and rebalancing occurs as necessary to maintain balances within established target ranges for these instruments. Cash equitization as employed by the Portfolio is a strategy pursuant to which the Portfolio will acquire certain derivative instruments, such as equity index futures, whereby the futures will be utilized to replicate index returns and enable the Portfolio to be fully invested, while still maintaining cash balances as needed by the Portfolio. This strategy works to limit the extent to which uninvested cash will weigh negatively on overall Portfolio returns when markets go up.The Index 600 Stock Portfolio’s ability to match the performance of the S&P SmallCap 600® Index will be affected to some extent by the size and timing of cash flows into and out of the Index 600 Stock Portfolio. The Portfolio will be managed with a view to reducing such effects. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index, and the risk of adverse price movements in the market. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include counterparty and liquidity risks. The Portfolio’s purchase of futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. •Equity Securities Risk – The value of equity securities, such as the stocks in which the Portfolio invests, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Exchange Traded Funds Risk – Investing in exchange traded funds (ETFs) may expose the Portfolio to greater risk of loss and price fluctuation than investing directly in a comparable portfolio of stocks comprising the index due to lack of liquidity, the additional expenses incurred as a shareholder in another investment company, and tracking error. ETFs are also subject to the risk that their market prices may trade at a premium or discount to their net asset value, which means the Portfolio will overpay for an ETF’s assets if it is trading at a premium and will get less than the value of the ETF’s assets when selling if it is trading at a discount. An active market for an ETF may not be developed or maintained. Trading of an ETF’s shares may be halted by the exchange, in which case the Portfolio would be unable to sell its ETF shares unless and until trading is resumed. •Indexing Strategy Risk –A Portfolio using a passive management strategy is not “actively” managed, and therefore does not engage in shifting portfolio assets to take advantage of market opportunity, and does not attempt to manage market volatility, use defensive strategies or reduce the effects of any long-term periods of poor stock performance. Since the Portfolio implements a full replication strategy with respect to the index which it tracks, to the extent the index has a significant allocation to an industry or group of industries, a particular sector, or to a single issuer or small number of issuers, the Portfolio will exhibit a significant investment level in that industry, group of industries, sector, issuer or small number of issuers. Portfolio performance may be adversely affected by a significant investment in an industry, group of industries, sector, issuer or small number of issuers, and may be more susceptible to adverse economic, market, political or regulatory developments affecting the industry, group of industries sector or issuer(s) subject to a significant level of investment. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Small Cap Company Risk – Investing in small cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Tracking Error Risk – The Portfolio may be subject to tracking error, which is the divergence of the Portfolio’s performance from that of the underlying index. Tracking error may occur due to a number of factors, including differences between the securities held in the Portfolio and those included in the underlying index, and based upon the fact that the Portfolio incurs fees and expenses, while the underlying index does not. Tracking error risk may be heightened during times of increased market volatility or other unusual market conditions. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Prior to February 1, 2021, the Portfolio was managed by Mason Street Advisors, LLC. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202031.17%Worst Quarter1st quarter, 2020-32.66% Best Quarter 2020-12-31 0.3117 Worst Quarter 2020-03-31 -0.3266 Average Annual Total Return(for periods ended December 31, 2023) 0.1576 0.1066 0.0829 0.1605 0.1104 0.0866 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0085 0 0.0003 0.0001 0.0089 -0.0001 0.0088 Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 90 283 492 1095 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 29.23% of the average value of its portfolio. 0.2923 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets in common stocks of companies with market capitalizations that do not exceed the maximum market capitalization of any security in the Russell 2000® Index at the time of purchase (approximately $59.14 billion as of March 31, 2024). The market capitalization of companies in the Portfolio and the Index changes over time and the Portfolio will not sell a stock just because the company has grown to a market capitalization outside of the range. The Portfolio may, on occasion, purchase companies with a market capitalization above the range. Securities falling outside of the market capitalization range noted above will be included in the overall calculation of assets but not counted as fulfilling the 80% minimum. The Portfolio may also invest in the equity securities of micro cap companies (defined as companies with stock market capitalizations less than $500 million at the time of investment).Reflecting a value approach to investing, the Portfolio will seek the stocks of companies whose current stock prices do not appear to adequately reflect their underlying value as measured by assets, earnings, cash flow or business franchises. The in-house research team at the adviser generally looks for some of the following:•low price/earnings, price/book value, or price/cash flow ratios relative to the Russell 2000® Index the company’s peers, or its own historical norm;•low stock price relative to a company’s underlying asset values;•above-average dividend yield relative to a company’s peers or its own historical norm;•a plan to improve the business through restructuring; and•a sound balance sheet and other positive financial characteristics.While the Portfolio does not seek to focus its investments in any particular economic sector, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector as a result of the adviser’s stock selection process. The adviser integrates environmental, social, and governance (ESG) factors into its investment research process for certain investments. While ESG matters vary widely, the adviser generally considers ESG factors such as climate change, resource depletion, labor standards, diversity, human rights issues, and governance structure and practices. For certain types of investments, including, but not limited to, cash, currency positions, and particular types of derivatives, an ESG analysis may not be relevant or possible due to lack of data. Where ESG considerations are integrated into the investment research process, the adviser focuses on the ESG factors that it considers most likely to have a material impact on the performance of the holdings in the Portfolio. The adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio.In pursuing its investment objective, the adviser has the discretion to deviate from its normal investment criteria, as described above, and purchase securities the adviser believes could provide an opportunity for substantial appreciation. These special situations might arise when the adviser believes a security could increase in value for a variety of reasons, including a change in management, a reorganization, a spin-off of a business line, a special dividend, or some other extraordinary corporate event, a new product introduction or innovation, or a favorable competitive environment.While most assets will be invested in U.S. common stocks, other securities may also be purchased, including American Depositary Receipts (ADRs) and foreign securities (up to 20% of net assets), real estate investment trust (REITs) and securities of other investment companies, including open-end funds, closed-end funds, exchange traded funds (ETFs) and business development companies (BDCs), in keeping with the Portfolio’s objectives.The Portfolio may sell securities for a variety of reasons, such as to secure gains, limit losses or redeploy assets into more promising opportunities. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Investment Style Risk – A portfolio managed using a value style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Micro Cap Company Risk – Investing in micro cap stocks may cause the Portfolio to experience more rapid and extreme changes in value than a fund that invests solely in small, mid and large cap stocks due to a more limited track record, narrower product markets, more limited resources, higher risk of failure, and less liquid trading markets. •Other Investment Companies Risk – The Portfolio will indirectly bear its pro rata portion of the expenses of the investment companies in which it invests, including advisory fees, in addition to the direct expenses of the Portfolio. The expenses associated with some business development companies may be significant. Investments in other investment companies are subject to market and selection risks, and generally entail the same risks as the underlying securities held by them. ETFs, closed-end funds and BDCs are also subject to the risk that their market prices may trade at a premium or a discount to their net asset value, which means the Portfolio will overpay for a fund’s assets if it is trading at a premium and will get less than the value of the fund’s assets when selling if it is trading at a discount. An active trading market for an ETF, closed-end fund or BDC may not be developed or maintained. In the event of a trading halt by the exchange, the Portfolio would be unable to sell its ETF, closed-end or BDC shares unless and until trading is resumed. BDCs invest in small and medium-sized private companies that may not have access to public equity markets. As a result, a BDC’s portfolio may be less liquid, may be more adversely affected by poor economic or market conditions, and may be adversely affected by risks associated with industries and sectors in which portfolio companies may concentrate. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Small Cap Company Risk – Investing in small cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Special Situation Risk – In special situations, the adviser may deviate from the Portfolio’s normal investment criteria when purchasing a security. In these special situations, there is the risk that the change or event anticipated by the adviser when purchasing a company might not occur or attract the expected attention, which could have a negative impact on the price of the company's securities. Investing in special situations may involve heightened volatility in the value of the securities purchased and may cause greater risk of loss. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202028.62%Worst Quarter1st quarter, 2020-31.21% Best Quarter 2020-12-31 0.2862 Worst Quarter 2020-03-31 -0.3121 Average Annual Total Return(for periods ended December 31, 2023) 0.1385 0.0943 0.0673 0.1465 0.1000 0.0676 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0059 0 0.0003 0.0062 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 63 199 346 774 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 21.49% of the average value of its portfolio. 0.2149 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio will invest at least 80% of net assets (plus any borrowings for investment purposes) in the securities of issuers from countries outside the United States. Countries located outside of the United States shall refer to:•securities of companies whose principal trading activities are outside the U.S.; or•securities denominated in non U.S. dollar currencies; or•securities of companies that: are organized under the laws of, or have principal offices in, a country other than the U.S., and derive 50% or more of their total revenue from either goods or services produced or sales made in markets outside the U.S.; or•American Depositary Receipts and American Depositary SharesThe Portfolio may invest in emerging markets but will normally limit such investments to 20% of its net assets, measured at the time of purchase. The adviser normally invests the Portfolio’s assets primarily in foreign common stocks and American Depositary Receipts (ADRs) and other depositary receipts. While the adviser normally allocates the Portfolio’s assets across different countries and regions, the Portfolio may invest a relatively large percentage of its assets in a single country, a small number of countries, or a particular geographic region. The Portfolio invests primarily in large capitalization companies, but may invest in companies of any size. Although the Portfolio primarily invests its assets in issuers located outside the U.S., it also invests in U.S. issuers.The adviser invests the Portfolio’s assets in companies it believes operate in a market environment, or with a competitive advantage, that make it difficult for competition to disrupt current and future profitability, in combination with growth drivers that may offer above-average growth potential measured by factors such as earnings or revenue. Companies with high growth potential tend to be companies with higher than average price/earnings (P/E) or price/book (P/B) ratios. Companies with strong growth potential often have new products, technologies, distribution channels, or other opportunities, or have a strong industry or market position. The stocks of these companies are often called “growth” stocks. In buying and selling securities for the Portfolio, the adviser relies on fundamental analysis, which involves a “bottom up” assessment of a company’s potential for success in light of factors such as its financial condition, earnings outlook, strategy, management, industry position, and economic and market conditions. While the Portfolio does not seek to focus its investments in any particular sector, the Portfolio may at times have a relatively high percentage of its assets invested in a particular sector as a result of the adviser’s stock selection process.The Portfolio may reduce or sell its position in a particular holding when the adviser believes a stock is fully valued, the conditions upon which the adviser based its original investment thesis no longer holds true, or due to portfolio construction considerations. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They, and other similar depositary receipts, are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs or other depositary receipts. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Foreign Currency Risk – The risk that foreign (non-U.S. dollar) currency denominated securities, or derivatives that provide exposure to foreign currencies, may be adversely affected by decreases in foreign currency values relative to the U.S. dollar. Investments in securities subject to foreign currency risk may have more rapid and extreme changes in value or more losses than investments in U.S. dollar denominated securities. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be less liquid, more volatile, and harder to value than U.S. securities. •Geographic Focus Risk – To the extent a relatively large percentage of the Portfolio’s assets are invested in issuers located in a single country, a small number of countries, or a particular geographic region, the Portfolio’s performance could be more volatile than that of a more geographically diversified fund, and the Portfolio’s performance may be more closely tied to the market, currency, economic, political, or regulatory conditions in those countries or that region. •Investment Style Risk – A portfolio managed using a growth style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Liquidity Risk – Markets for small cap stocks and foreign securities, in particular emerging markets securities, may be less liquid than markets for larger cap stocks and domestic securities, and therefore may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Small and Mid Cap Company Risk – Investing in small and mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance and the returns of an additional index of securities with characteristics similar to those that the Portfolio typically holds. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance and the returns of an additional index of securities with characteristics similar to those that the Portfolio typically holds. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202017.75%Worst Quarter1st quarter, 2020-17.19% Best Quarter 2020-06-30 0.1775 Worst Quarter 2020-03-31 -0.1719 Average Annual Total Return(for periods ended December 31, 2023) 0.2077 0.1133 0.0599 0.1758 0.0881 0.0515 0.1403 0.0749 0.0455 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to seek capital appreciation. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0076 0 0.0004 0.0080 -0.0008 0.0072 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 74 247 436 982 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 14.86% of the average value of its portfolio. 0.1486 PRINCIPAL INVESTMENT STRATEGIES The Portfolio normally invests primarily in foreign equity securities, including emerging market equity securities. The Portfolio normally invests its assets across different industries, sectors, countries, and regions, but the Portfolio may invest a significant percentage of its assets in issuers in a single industry, sector, country, or a particular geographic region.In conjunction with a team of investment research analysts, sector leaders select investments for the Portfolio. The adviser generally manages the Portfolio to align with the MSCI EAFE® (Europe-Australasia-Far East) Index (the “Index”) with respect to sector weightings. The Portfolio does not, as a matter of policy, concentrate in any particular industry. The Portfolio is not constrained by any particular investment style. The adviser may invest the Portfolio’s assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies), in the stocks of companies it believes are undervalued compared to their perceived worth (value companies), or in a combination of growth and value companies. The Portfolio’s investments in equity securities may include securities of companies of any capitalization level, and could include common stocks, preferred stocks, securities convertible into stock and American Depositary Receipts (ADRs) and other depositary receipts for those securities.The adviser uses an active “bottom up” investment approach to buying and selling investments for the Portfolio, which emphasizes individual stock selection. Investments are selected primarily based on fundamental analysis of individual issuers and their potential in light of their financial condition, and market, economic, political and regulatory conditions. Factors considered may include analysis of an issuer’s earnings, cash flows, competitive position and management ability. The adviser may also consider environmental, social and governance (ESG) factors in its fundamental investment analysis where the adviser believes such factors could materially impact the economic value of an issuer. ESG factors considered may include, but are not limited to, climate change, resource depletion, an issuer's governance structure and practices, data protection and privacy issues, and diversity and labor practices. Consideration of ESG factors may not be determinative in the adviser’s investment process and the adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio. Quantitative screening tools that systematically evaluate an issuer’s valuation, price and earnings momentum, earnings quality and other factors, may also be considered.The adviser may sell securities for a variety of reasons such as to seek to secure gains, limit losses, or redeploy assets into opportunities believed to be more promising, among others. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They, and other similar depositary receipts, are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs or other depositary receipts. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Convertible Securities Risk – Convertible securities (which can be bonds, notes, debentures, preferred stock, or other securities which are convertible into or exercisable for common stock), are subject to both the credit and interest rate risks associated with fixed income securities and to the stock market risk associated with equity securities. The value of a convertible security may not increase or decrease as rapidly as the underlying common stock. The Portfolio may be forced to convert a security before it would otherwise choose, which may have an adverse effect on the Portfolio’s ability to achieve its investment objective. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common and preferred stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Currency Risk – The risk that foreign (non-U.S. dollar) currency denominated securities, or derivatives that provide exposure to foreign currencies, may be adversely affected by decreases in foreign currency values relative to the U.S. dollar. Investments in securities subject to foreign currency risk may have more rapid and extreme changes in value or more losses than investments in U.S. dollar denominated securities. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be less liquid, more volatile, and harder to value than U.S. securities. •Geographic Focus Risk – The Portfolio’s performance could be more volatile than that of a more geographically diversified fund and could be significantly impacted as a result of the Portfolio investing a large percentage of its assets in issuers located in a single country, a small number of countries, or a particular geographic region. Also, the Portfolio’s performance may be more closely tied to the market, currency, economic, political, or regulatory conditions in those countries or that region. •Investment Style Risk – A portfolio managed using a particular style of investing, such as growth or value or a combination of both, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Liquidity Risk – Markets for small cap stocks and foreign securities, in particular emerging markets securities, may be less liquid than markets for larger cap stocks and domestic securities, and therefore may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Preferred Stocks Risk – Preferred stocks often lack a fixed maturity or redemption date and are therefore more susceptible to price fluctuations when interest rates change. They also carry a greater risk of non-receipt of income because unlike interest on debt securities, dividends on preferred stocks must be declared by the issuer’s board of directors before becoming payable. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector or industries within a sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Small and Mid Cap Company Risk – Investing in small and mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance and the returns of an additional index of securities with characteristics similar to those that the Portfolio typically holds. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance and the returns of an additional index of securities with characteristics similar to those that the Portfolio typically holds. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202016.69%Worst Quarter1st quarter, 2020-19.69% Best Quarter 2020-06-30 0.1669 Worst Quarter 2020-03-31 -0.1969 Average Annual Total Return(for periods ended December 31, 2023) 0.1295 0.0882 0.0442 0.1562 0.0708 0.0383 0.1824 0.0816 0.0428 INVESTMENT OBJECTIVE The investment objective of the Portfolio is long-term growth of capital and income. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0066 0 0.0002 0.0068 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 69 218 379 847 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 14.23% of the average value of its portfolio. 0.1423 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in equity securities, with such securities issued primarily by non-U.S. companies. The Portfolio will normally hold securities of issuers from at least three different countries (not including the U.S.). The Portfolio’s equity investments may include common stocks, depositary receipts evidencing ownership of common stocks, certain preferred stocks, and securities that carry the right to buy common stocks (e.g., rights and warrants). The Portfolio may purchase securities in any country, including those with developed markets and emerging markets and is not required to allocate its investments in set percentages in particular countries, except that the Portfolio’s investments in emerging markets countries normally will be limited to 30% of its net assets. From time to time, the Portfolio may have significant investments in one or more countries, a geographic region, or in particular sectors. The Portfolio may enter into currency forward contracts in order to hedge direct or indirect foreign currency exposure.The Portfolio typically invests in well-established companies of medium-to-large capitalization based on standards of the applicable market. The Portfolio typically invests in companies that, in the adviser’s opinion, appear to be temporarily undervalued but have a favorable outlook for long- term growth. The Portfolio’s adviser also focuses on the underlying financial condition and prospects of individual companies, including future earnings, cash flow, and dividends. Various other factors, including financial strength, economic condition, competitive advantage, quality of the business franchise, financially material environmental, social, and governance (“ESG”) issues (for example, the management of environmental risk, employee relations, and shareholder rights), along with the reputation, experience, and competence of a company’s management are weighed against valuation in selecting individual securities. Consideration of ESG factors may not be determinative in the adviser’s investment process and the adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio. The adviser also considers the economic and political stability of the country where the issuer is located and the protections provided to shareholders.The adviser may consider selling an equity security when it believes the security is no longer undervalued, due to either its price appreciation or changes in the company’s fundamentals, or when the adviser believes another security provides a more attractive investment opportunity. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They, and other similar depositary receipts, are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs or other depositary receipts. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The Portfolio’s use of derivatives involves risks different from, or possibly greater than, the risks associated with investing directly in securities or other traditional investments. Investments in derivatives may not have the intended effects and may result in losses for the Portfolio that may not otherwise have occurred or missed opportunities for the Portfolio. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. The derivatives could involve management, credit, interest rate, liquidity and market risks, and the risks of misplacing or improper valuation. Changes in the value of the derivative may not correlate as intended with the underlying asset, rate or index. In addition, the Portfolio could sustain a loss in the event the counterparty to a derivatives transaction fails to make the required payments or otherwise comply with the terms of the contract. The Portfolio’s purchase of forwards contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. In addition, the purchase of forwards also involves counterparty credit risk as well as heightened market risk. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Currency Risk – The risk that foreign (non-U.S. dollar) currency denominated securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar. Investments in securities subject to foreign currency risk may have more rapid and extreme changes in value or more losses than investments in U.S. dollar denominated securities. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be less liquid, more volatile, and harder to value than U.S. securities. •Geographic Focus Risk – The Portfolio’s performance could be more volatile than that of a more geographically diversified fund and could be significantly impacted as a result of the Portfolio investing a relatively large percentage of its assets in issuers located in a single country, a small number of countries, or a particular geographic region. Also, the Portfolio’s performance may be more closely tied to the market, currency, economic, political, or regulatory conditions in those countries or that region. •Investment Style Risk – A portfolio managed using a value style of investing, such as the Portfolio, may underperform when the market does not favor the particular style used by the Portfolio. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Liquidity Risk – Markets for foreign securities, in particular emerging markets securities, may be less liquid than markets for larger cap stocks and domestic securities, and therefore may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mid Cap Company Risk – Investing in mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •Warrants Investing Risk – Investments in warrants may be more volatile than the underlying common stock and may cause the Portfolio increased risk of loss if the warrants cannot be exercised prudently by the expiration date or if the warrants lack a liquid secondary market for resale. Warrants can provide exposure to an underlying stock for a portion of the price of direct ownership of shares of that stock. As a result, most warrants have some degree of leverage, which can vary depending on the type of warrant. This means that small changes in the value of the underlying stock results in larger changes in the value of the warrant. This can magnify gains when stock prices rise, but it can also magnify losses when stock prices fall. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance and the returns of an additional index of securities with characteristics similar to those that the Portfolio typically holds. Prior to November 1, 2021, the Portfolio was managed by a different sub-adviser. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance and the returns of an additional index of securities with characteristics similar to those that the Portfolio typically holds. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202215.79%Worst Quarter1st quarter, 2020-24.42% Best Quarter 2022-12-31 0.1579 Worst Quarter 2020-03-31 -0.2442 Average Annual Total Return(for periods ended December 31, 2023) 0.1609 0.0447 0.0168 0.1730 0.0634 0.0292 0.1562 0.0708 0.0383 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to seek capital appreciation. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0105 0 0.0005 0.0110 -0.0019 0.0091 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 93 331 588 1323 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 24.47% of the average value of its portfolio. 0.2447 PRINCIPAL INVESTMENT STRATEGIES The Portfolio normally invests at least 80% of its net assets (plus any borrowings for investment purposes) in equity securities of issuers that are tied economically to emerging market countries. The Portfolio invests primarily in common stocks, but may also invest in other types of equity securities, including but not limited to, preferred stocks and American Depositary Receipts (ADRs) and other depositary receipts for those securities.Emerging market countries include countries determined by the Portfolio’s adviser to have emerging market economies, taking into account a number of factors, such as the country’s credit rating, its political and economic stability and the development of its financial and capital markets. Emerging market countries include, but are not limited to, all countries that comprise the MSCI Emerging Markets Index. A company is considered to be an emerging market company if the adviser determines that the company meets one or more of the following criteria: the company•is organized under the laws of, or has its principal office in an emerging market country;•has its principal securities trading market in an emerging market country; and/or•derives the majority of its annual revenue or earnings or assets from goods produced, sales made or services performed in an emerging market country.The Portfolio may also invest in equity securities of issuers that are not tied economically to emerging market countries. Such investments will not exceed 20% of the net assets of the Portfolio. The Portfolio may invest in securities denominated in U.S. Dollars and currencies of emerging market countries in which it is permitted to invest. The Portfolio typically has full currency exposure to those markets in which it invests.The Portfolio may invest in companies of any size. The Portfolio may invest in securities of any market sector and, from time to time, as a result of the adviser’s stock selection process, may hold a significant amount of securities of companies within a single sector. The adviser may invest a large percentage of the Portfolio’s assets in issuers in a single country, a small number of countries, or a particular geographic region. The Portfolio currently anticipates that it will have significant exposure to Mainland China equity and equity-related securities including through the Shanghai-Hong Kong and Shenzhen-Hong Kong Stock Connect program or by any other available means.In seeking to achieve the Portfolio’s investment objective the adviser invests in quality companies and is an active, engaged owner. The adviser evaluates every company against quality criteria and builds conviction using a team-based approach and peer review process. The quality assessment covers five key factors: 1) the durability of the business model, 2) the attractiveness of the industry, 3) the strength of financials, 4) the capability of management, and 5) the most material environmental, social and governance (“ESG”) factors impacting a company. Examples of ESG factors considered by the adviser include, but are not limited to, carbon emissions, climate risks, labor management, employee safety and corporate governance. The specific factors considered may vary depending on the type of company being evaluated. Consideration of ESG factors may not be determinative in the adviser’s investment process and the adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio. The adviser seeks to understand what is changing in companies, industries and markets but is not being priced into the market or is being mispriced. Through fundamental research, supported by a global research presence and proprietary tools, the adviser seeks to identify companies whose quality is not yet fully recognized by the market. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •ADR Risk – ADRs are receipts representing ownership of shares of a foreign issuer held by a U.S. bank or similar financial institution that entitle the holder to dividends and capital gains on the underlying foreign shares. ADRs are alternatives to directly purchasing the underlying foreign securities in their national markets and currencies. They, and other similar depositary receipts, are subject to many of the risks associated with direct investments in foreign securities, such as currency risk, political and economic risk and market risk, because their values depend on the performance of the non-dollar denominated underlying foreign securities. The Portfolio is also subject to fees and the credit risk of the financial institution holding the ADRs or other depositary receipts. ADRs may be “sponsored,” meaning that they are implemented by a financial institution in collaboration with the issuing foreign company, or “unsponsored,” meaning that the financial institution created the instrument without the sponsorship or direct involvement of the foreign company. Differing registration requirements apply to each type of ADR. ADRs may transact on exchanges or on over-the-counter markets (“OTC”). Conducting transactions in OTC markets may result in higher costs, a lack of pricing transparency and lower liquidity when compared with exchange-based transactions. Risks associated with different ADR types will vary, based upon differences in registration, reporting and disclosure requirements that apply to such ADRs and the characteristics of the market in which transactions for the particular ADR are conducted. •China Investing Risk – Hong Kong reverted to Chinese sovereignty on July 1, 1997, and investments in Hong Kong are subject to certain risks associated with investments in China. Risks associated with investments in China and Hong Kong include exposure to currency fluctuations, less liquidity, expropriation, confiscatory taxation, nationalization, exchange control regulations (including currency blockage) and differing legal standards. Inflation and rapid fluctuations in inflation and interest rates have had, and may continue to have, negative effects on the economies and securities markets of China or Hong Kong. Military conflicts, either in response to internal social unrest or conflicts with other countries, are an ever present consideration. The adoption or continuation of protectionist trade policies by one or more countries (including the U.S.) could lead to decreased demand for Chinese products and have an adverse effect on the Chinese securities markets. In particular, the current political climate has intensified concerns about heightened trade tensions between China and the U.S., as each country has imposed, and may in the future impose additional, tariffs on the other country’s products. These actions may result in a significant reduction in international trade, the oversupply of certain manufactured goods, substantial price reductions of goods and possible failure of individual companies and/or large segments of China’s export industry, which could have a negative impact on a Portfolio’s performance. The Portfolio may gain exposure to companies based or operated in China by investing through legal structures known as variable interest entities (“VIEs”) which utilize offshore companies established by the Chinese company to facilitate foreign investment. Instead of directly owning the equity securities of a Chinese company, a VIE enters into service and other contracts with the Chinese company. These contractual arrangements are intended to give the offshore company the ability to exercise power over and obtain economic rights from the Chinese company. Among the risks related to owning VIEs is the risk that the Chinese government could intervene with respect to the use of the VIE structure, which could significantly affect the Chinese company’s performance and the terms and ultimate enforceability of the VIE’s contractual arrangement with the Chinese company. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common and preferred stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Currency Risk – The risk that foreign (non-U.S. dollar) currency denominated securities, or derivatives that provide exposure to foreign currencies, may be adversely affected by decreases in foreign currency values relative to the U.S. dollar. Investments in securities subject to foreign currency risk may have more rapid and extreme changes in value or more losses than investments in U.S. dollar denominated securities. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be less liquid, more volatile, and harder to value than U.S. securities. •Geographic Focus Risk – The Portfolio’s performance could be more volatile than that of a more geographically diversified fund and could be significantly impacted as a result of the Portfolio investing a large percentage of its assets in issuers located in a single country, a small number of countries, or a particular geographic region. Also, the Portfolio’s performance may be more closely tied to the market, currency, economic, political, or regulatory conditions in those countries or that region. •Large Cap Company Risk – Investing in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Liquidity Risk – Markets for small and micro cap stocks and foreign securities, in particular emerging markets securities, may be less liquid than markets for larger cap stocks and domestic securities, and therefore may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. The lack of active trading markets may make it difficult to obtain an accurate price for a security held by the Portfolio. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Preferred Stocks Risk – Preferred stocks often lack a fixed maturity or redemption date and are therefore more susceptible to price fluctuations when interest rates change. They also carry a greater risk of non-receipt of income because unlike interest on debt securities, dividends on preferred stocks must be declared by the issuer’s board of directors before becoming payable. •Sector Focus Risk – To the extent the Portfolio invests a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio is underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Small and Mid Cap Company Risk – Investing in small and mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Prior to March 24, 2017, the sub-adviser to the Portfolio was different. Performance shown may have been different if the current strategy, and the current sub-adviser, had been in place during the periods shown. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 202026.43%Worst Quarter1st quarter, 2020-26.40% Best Quarter 2020-12-31 0.2643 Worst Quarter 2020-03-31 -0.2640 Average Annual Total Return(for periods ended December 31, 2023) 0.0691 0.0313 0.0144 0.0983 0.0368 0.0266 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to realize maximum current income to the extent consistent with liquidity and stability of capital. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0030 0 0.0003 0.0033 0.0000 0.0033 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 34 106 185 418 PRINCIPAL INVESTMENT STRATEGIES As a government money market portfolio, the Portfolio invests at least 99.5% of its total assets in cash, U.S. Treasury bills, notes and other obligations issued or guaranteed as to principal and interest by the U.S. Government, its agencies or instrumentalities, and repurchase agreements secured by such obligations or cash. The Portfolio may invest 100% of its total assets in such repurchase agreements. Under normal circumstances, the Portfolio will invest at least 80% of its net assets in obligations issued or guaranteed as to principal and interest by the U.S. Government, its agencies or instrumentalities, and repurchase agreements secured by such obligations. The Portfolio invests in a portfolio of securities maturing in 397 days or less (with certain exceptions) that will have a dollar-weighted average maturity of 60 days or less and a dollar-weighted average life of 120 days or less. The Portfolio may invest in variable and floating rate instruments, and transact in securities on a when-issued, delayed delivery or forward commitment basis. The Portfolio seeks to maintain a net asset value of $1.00 per share. PRINCIPAL RISKS •Active Management Risk – The securities selected for the Portfolio may underperform the markets, relevant indices, or securities selected by other funds with similar investment objectives and investment strategies. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security or the counterparty to a repurchase agreement is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Income Risk – The risk that the Portfolio’s yield will vary as short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates. •Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments is likely to decline. A low or negative interest rate environment poses additional risks to the Portfolio. Low yields on the Portfolio’s holdings may have an adverse impact on the Portfolio’s ability to provide a positive yield to its shareholders or pay expenses out of Portfolio assets. Additionally, securities issued or guaranteed by the U.S. government, its agencies and instrumentalities have historically involved little risk of loss of principal if held to maturity. However, due to fluctuations in interest rates, the market value of such securities may vary during the period you are invested in the Portfolio. For example, the market value of a fixed income portfolio with an average duration of five years generally would be expected to fall approximately 5% if interest rates rose by one percentage point. Declining interest rates may increase the risk that an issuer calls outstanding securities prior to their maturity. •Liquidity Risk – Investments for the Portfolio may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. The liquidity requirements applicable to government money market funds are designed to help mitigate the potential impact of these risks. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Repurchase Agreements Risk – If the other party to a repurchase agreement defaults on its obligation under the agreement, the Portfolio may suffer delays and incur costs or lose money in exercising its rights under the agreement. These risks may be heightened if the other party is located outside of the U.S. If the seller fails to repurchase the security and the market value of the security declines, the Portfolio may lose money. •Stable Net Asset Value Risk – The Portfolio may not be able to maintain a stable net asset value (“NAV”) of $1.00 per share at all times. If the Portfolio fails to maintain a stable NAV (or there is a perceived threat of such failure), the Portfolio, along with other money market funds, could be subject to increased redemption activity. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •U.S. Government Securities Risk – Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the Portfolio does not apply to the market value of such security or to shares of the Portfolio itself. •Variable and Floating Rate Instrument Risk – Variable and floating rate securities provide for a periodic adjustment in the interest rate paid on the obligations. The absence of an active market for these securities could make it difficult for the Portfolio to dispose of them if the issuer defaults. •When-Issued and Delayed Delivery Transactions Risk – When issued and delayed delivery securities involve the risk that the security will lose value prior to its delivery. There is also the risk that the security will not be issued or that the other party to the transaction will not meet its obligation. If this occurs, the Portfolio loses both the investment opportunity for the assets it set aside to pay for the security and any gain the security’s price. You could lose money by investing in the Government Money Market Portfolio. Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Portfolio is not a bank account and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Portfolio’s sponsor has no legal obligation to reimburse the Portfolio for losses and you should not expect that the sponsor will provide financial support to the Portfolio at any time, including during periods of market stress. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods.Returns are based on past results and are not an indication of future performance. Prior to May 1, 2016, the Portfolio operated as a prime money market fund and invested in certain types of securities that the Portfolio is no longer permitted to hold. Consequently, the performance information below may have been different if the current investment limitations had been in effect during the period prior to the Portfolio’s conversion to a government money market fund. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 20231.30%Worst Quarter1st quarter, 20220.00% Best Quarter 2023-12-31 0.0130 Worst Quarter 2022-03-31 0.0000 Average Annual Total Return(for periods ended December 31, 2023) 0.0483 0.0168 0.0107 For the seven-day period ended March 31, 2024, the Government Money Market Portfolio’s yield was5.03%. For the seven-day period ended March 31, 2024, the Government Money Market Portfolio’s yield was 0.0503 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to provide as high a level of current income as is consistent with prudent investment risk. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0032 0 0.0007 0.0039 Restated to reflect current expenses. Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 40 125 219 493 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 55.53% of the average value of its portfolio. 0.5553 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in a diversified portfolio of investment grade debt securities. Investment grade securities are generally securities rated investment grade by major credit rating agencies (BBB- or higher by S&P; Baa3 or higher by Moody’s; BBB- or higher by Fitch) or, if unrated, determined by the Portfolio’s adviser to be of comparable quality. Also, the Portfolio may invest up to 20% of net assets in foreign securities, including those of issuers located in emerging markets, consistent with its investment objective. Foreign securities held by the Portfolio may consist of both U.S. dollar and non-U.S. dollar denominated securities. Debt securities may be of any maturity, but under normal market conditions, the Portfolio’s effective dollar-weighted average maturity will not exceed three years. The Portfolio primarily invests in corporate, government and mortgage- and asset-backed securities. The Portfolio’s mortgage-related securities investments may include collateralized mortgage obligations as well as commercial and residential mortgage-backed securities. The Portfolio’s investments in asset-backed securities include asset-backed auto loans. The Portfolio may also invest in Rule 144A securities. The Portfolio may also utilize futures and forward contracts primarily to adjust the Portfolio’s duration and yield curve exposure, as well as to hedge foreign currency exposure. The Portfolio may invest in swap agreements, including the purchase or sale of credit default swaps and interest rate swaps (to take a position on interest rates moving either up or down) in keeping with its investment objective. Duration is a measure of the sensitivity of the price of a Portfolio’s fixed income securities to changes in interest rates; the longer the duration, the more sensitive the price will be to changes in interest rates.The adviser uses both a “top down” and “bottom up” investment approach to construct the portfolio of investments. The top down investment approach involves an evaluation by the adviser of the overall macroeconomic environment and its potential impact on the level and direction of interest rates. The adviser then identifies sectors it believes have the best potential for performance based on its economic outlook. The bottom up investment approach focuses on fundamental research of individual issuers. The adviser integrates environmental, social, and governance (ESG) factors into its investment research process for certain investments. While ESG matters vary widely, the adviser generally considers ESG factors such as climate change, resource depletion, labor standards, diversity, human rights issues, and governance structure and practices. For certain types of investments, including, but not limited to, cash, currency positions, and particular types of derivatives, an ESG analysis may not be relevant or possible due to lack of data. Where ESG considerations are integrated into the investment research process, the adviser focuses on the ESG factors that it considers most likely to have a material impact on the performance of the holdings in the Portfolio. The adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio.Investment decisions reflect the adviser’s outlook for interest rates and the economy, as well as the prices, yields, and credit quality of various securities in which the Portfolio may invest.The adviser may sell a portfolio security for a variety of reasons, such as to adjust the Portfolio’s average maturity, duration, or overall credit quality or to shift assets into and out of higher-yielding or lower-yielding securities or certain sectors. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected and the adviser’s quality determinations with respect to securities that are unrated by the major credit rating agencies may be inaccurate, which could cause the Portfolio to underperform other mutual funds or lose money. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Debt Obligations of Foreign Governments Risk – The issuer of the foreign debt or the governmental authorities that control the repayment of such debt may be unable or unwilling to repay principal or interest when due, and the Portfolio may have limited recourse in the event of a default. The market prices of debt obligations of governments and their agencies, and the Portfolio’s net asset value, may be more volatile than prices of U.S. debt obligations. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index, the risk of adverse price movements in the market and the risk that the counterparty to a derivatives transaction fails to make the required payment or otherwise comply with the terms of the contract. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include management, interest rate, and liquidity risks, and the risk of missed opportunities in other investments. The Portfolio’s purchase of forwards and futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. In addition, the purchase of forwards also involves counterparty credit risk as well as heightened market risk. The Portfolio’s purchase of swap agreements may pose risk arising from losses if the underlying reference asset does not perform as anticipated; such agreements are also subject to counterparty credit, liquidity and leveraging risks. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments is likely to decline. A significant rise in interest rates over a short period of time could cause significant losses in the market value of the Portfolio’s fixed income instruments. A portfolio with a longer average portfolio duration will be more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration. For example, the market value of a fixed income portfolio with an average duration of five years generally would be expected to fall approximately 5% if interest rates rose by one percentage point. Declining interest rates may increase the risk that an issuer calls outstanding securities prior to their maturity. •LIBOR Transition Risk – The risk related to the discontinuation of the London Interbank Offered Rate (“LIBOR”). Certain instruments held by the Portfolio may utilize LIBOR as their reference or benchmark rate. LIBOR had been used extensively in the U.S. and globally as the reference rate for various commercial and financial contracts, including corporate and municipal bonds and loans, floating rate mortgages, asset-backed securities, consumer loans, and derivatives. Although the transition process away from LIBOR for most instruments has been completed as of June 30, 2023, some LIBOR use is continuing and there may be potential effects related to the continued use of LIBOR on the Portfolio or on certain instruments in which the Portfolio invests. The continued transition process may involve, among other things, increased volatility or illiquidity in markets for instruments that currently rely on LIBOR and may result in a reduction in value of certain instruments held by the Portfolio. •Liquidity Risk – Fixed income and derivative investments can be difficult to purchase or sell at an advantageous time or price, if at all, during periods of reduced marketability for the investment or due to the size of the transaction. These risks may be magnified during periods of economic turmoil or in an extended economic downturn or when investing in emerging markets. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mortgage- and Asset-Backed Securities Risk – The Portfolio invests in collateralized mortgage obligations, mortgage-backed securities and asset-backed securities. Mortgage-related and other asset-backed securities are subject to interest rate risk, credit risk and liquidity risk as well as additional risks including prepayment and extension risk. Mortgage-related and other asset-backed securities represent interests in pools of mortgages or other assets and often involve risks that are different or possibly more acute than risks associated with other types of debt instruments. The value of some mortgage- or asset-backed securities may be particularly sensitive to changes in prevailing interest rates. Asset-backed securities are subject to risks similar to those associated with mortgage-backed securities, as well as risks associated with the nature and servicing of the assets underlying the securities. Asset-backed auto loans are backed by receivables from motor vehicle installment sales contracts or installment loans secured by motor vehicles and may be subject to heightened credit risk. •Prepayment and Extension Risk – Prepayment risk is the risk that principal on a debt obligation will be paid earlier than scheduled or expected, which could reduce yield and market value of the security and shorten the Portfolio’s average effective maturity. The rate of prepayments tends to increase as interest rates fall. Extension risk is the risk that, as interest rates rise, repayments on a debt obligation may occur more slowly than anticipated by the market and the obligation may remain outstanding longer. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •U.S. Government Securities Risk – Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the Portfolio does not apply to the market value of such security or to shares of the Portfolio itself. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 20204.14%Worst Quarter1st quarter, 2022-2.56% Best Quarter 2020-06-30 0.0414 Worst Quarter 2022-03-31 -0.0256 Average Annual Total Return(for periods ended December 31, 2023) 0.0526 0.0180 0.0144 0.0461 0.0151 0.0127 INVESTMENT OBJECTIVE The primary investment objective of the Portfolio is to provide as high a level of total return as is consistent with prudent investment risk. A secondary objective is to seek preservation of shareholders' capital. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0030 0 0.0001 0.0031 0.0000 0.0031 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio's operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 32 100 174 393 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 248.02% of the average value of its portfolio. 2.4802 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in a diversified portfolio of investment grade debt securities with maturities exceeding one year. Investment grade securities are generally securities rated investment grade by major credit rating agencies (BBB- or higher by S&P; Baa3 or higher by Moody’s; BBB- or higher by Fitch) or, if unrated, determined by the Portfolio’s adviser to be of comparable quality. The Portfolio invests primarily in U.S Government obligations, mortgage-backed securities, including commercial mortgage-backed securities, collateralized mortgage obligations, agency mortgage-backed securities, non-agency mortgages, corporate bonds, and asset-backed securities. The Portfolio may invest in certain derivative instruments, including to-be-announced and long settle mortgage-backed securities issued by a Federal agency, subject to the Portfolio’s objective and the Fund’s policies. Mortgage dollar rolls may also be used. The Portfolio may invest in Rule 144A securities. Additionally, the Portfolio may invest up to 20% of net assets in foreign securities, consistent with its investment objectives. Foreign securities held by the Portfolio consist primarily of U.S. dollar denominated securities. Debt securities may be of any maturity or duration, but under normal market conditions, the Portfolio attempts to maintain an overall dollar-weighted average effective duration that is within 10% of the Bloomberg® U.S. Aggregate Index, which had a duration of 6.21 years as of March 31, 2024. Duration is a measure of the sensitivity of the price of the Portfolio’s fixed income securities to changes in interest rates; the longer the duration, the more sensitive the price will be to changes in interest rates. The Portfolio does not target an average effective maturity.The adviser uses a fundamental, relative value investment approach to construct the portfolio of investments. The adviser invests in debt securities that it believes offer competitive returns and are undervalued, offering additional income and/or price appreciation potential relative to other debt securities of similar credit quality and interest rate sensitivity. The adviser may engage in active and frequent trading of portfolio securities to achieve its investment objectives.The adviser may sell a portfolio security that has achieved its desired return or if the adviser believes the security or its sector has become overvalued. The adviser may also sell a security if a more attractive opportunity becomes available or if the security is no longer attractive due to its risk profile or as a result of changes in the overall market environment. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected and the adviser’s quality determinations with respect to securities that are unrated by the major credit rating agencies may be inaccurate, which could cause the Portfolio to underperform other mutual funds or lose money. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Debt Obligations of Foreign Governments Risk – The issuer of the foreign debt or the governmental authorities that control the repayment of such debt may be unable or unwilling to repay principal or interest when due, and the Portfolio may have limited recourse in the event of a default. The market prices of debt obligations of governments and their agencies, and the Portfolio’s net asset value, may be more volatile than prices of U.S. debt obligations. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index and the risk of adverse price movements in the market. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include counterparty and liquidity risks. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be less liquid, more volatile, and harder to value than U.S. securities. •High Portfolio Turnover Risk – Active and frequent trading may cause higher brokerage expenses and other transaction costs, which may adversely affect the Portfolio’s performance. •Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments is likely to decline. A significant rise in interest rates over a short period of time could cause significant losses in the market value of the Portfolio’s fixed income instruments. A portfolio with a longer average portfolio duration will be more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration. For example, the market value of a fixed income portfolio with an average duration of five years generally would be expected to fall approximately 5% if interest rates rose by one percentage point. Declining interest rates may increase the risk that an issuer calls outstanding securities prior to their maturity. •Liquidity Risk – Fixed income investments, including Rule 144A securities, may be difficult to purchase or sell at an advantageous time or price, if at all, during periods of reduced marketability for the investment or due to the size of the transaction. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mortgage- and Asset-Backed Securities Risk – The risks of investing in mortgage-related and other asset-backed securities, including mortgage dollar rolls, include interest rate risk, credit risk, liquidity risk, prepayment risk and extension risk. Mortgage-related and other asset-backed securities represent interests in pools of mortgages or other assets and often involve risks that are different or possibly more acute than risks associated with other types of debt instruments. The value of some mortgage- or asset-backed securities may be particularly sensitive to changes in prevailing interest rates. To-be-announced mortgage-backed securities increase interest rate risks because the underlying mortgages may be less favorable than anticipated by the Portfolio. Other asset-backed securities are subject to risks similar to those associated with mortgage-backed securities, as well as risks associated with the nature and servicing of the assets underlying the securities. Asset-backed securities may not have the benefit of a security interest in collateral comparable to that of mortgage assets, resulting in additional credit risk. The use of mortgage dollar rolls involves potential risks of loss that are different from those related to the mortgage securities underlying the transactions, including counterparty risk, market risk, and financial risk (including the risk that the value of the principal and interest payments associated with the mortgage instrument sold to a counterparty exceeds the compensation paid to the Portfolio by the counterparty). •Prepayment and Extension Risk – Prepayment risk is the risk that principal on a debt obligation will be paid earlier than scheduled or expected, which could reduce yield and market value of the security and shorten the Portfolio’s average effective maturity. The rate of prepayments tends to increase as interest rates fall. Extension risk is the risk that, as interest rates rise, repayments on a debt obligation may occur more slowly than anticipated by the market and the obligation may remain outstanding longer. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •U.S. Government Securities Risk – Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the Portfolio does not apply to the market value of such security or to shares of the Portfolio itself. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter4th quarter, 20236.87%Worst Quarter1st quarter, 2022-6.05% Best Quarter 2023-12-31 0.0687 Worst Quarter 2022-03-31 -0.0605 Average Annual Total Return(for periods ended December 31, 2023) 0.0619 0.0141 0.0194 0.0553 0.0110 0.0181 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to seek maximum total return, consistent with preservation of capital and prudent investment management. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0055 0 0.0166 0.0221 -0.0005 0.0216 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio’s operating expenses due to the expense reimbursement agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 219 686 1180 2540 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 32.15% of the average value of its portfolio. 0.3215 PRINCIPAL INVESTMENT STRATEGIES The Portfolio seeks to achieve its investment objective by investing under normal circumstances at least 80% of its net assets (plus any borrowings for investment purposes) in a diversified portfolio of fixed income securities that are issued or guaranteed by the U.S. Government, its agencies or government sponsored enterprises (“U.S. Government Securities”), which may be represented by forwards or derivatives such as options, futures contracts or interest rate swap agreements (to take a position on interest rates moving either up or down). Assets not invested in U.S. Government Securities may be invested in other types of investment grade fixed income instruments, such as corporate debt securities of U.S. issuers and mortgage- and asset-backed securities, subject to the quality restrictions described below. Mortgage-related securities may include mortgage pass-through securities, collateralized mortgage obligations, commercial mortgage-backed securities and mortgage dollar rolls. The Portfolio may also invest up to 10% of its net assets in preferred stocks.The Portfolio will normally have a minimum average portfolio duration of eight years and, for point of reference, the dollar-weighted average maturity of the Portfolio, under normal circumstances, is expected to be more than ten years. Duration is a measure of the sensitivity of the price of the Portfolio’s fixed income securities to changes in interest rates; the longer the duration, the more sensitive the price will be to changes in interest rates.The Portfolio may invest all of its assets in derivative instruments, such as options, futures contracts or interest rate swap agreements (to take a position on interest rates moving either up or down), or in mortgage- or asset-backed securities, subject to the Portfolio’s objective and the Fund’s policies. The adviser may invest in derivatives at any time it deems appropriate. It will generally do so when it believes that U.S. Government Securities are overvalued relative to derivative instruments or to adjust the overall duration of the Portfolio. The potential leverage created by use of derivatives may cause the Portfolio to be more sensitive to interest rate movements and thus more volatile than other long-term U.S. government bond funds that do not use derivatives.The Portfolio may purchase or sell securities on a when-issued, delayed delivery or forward commitment basis and may engage in short sales. A short sale involves the sale of a security that is borrowed from a broker or other institution, and which must be purchased in the market at a later date and returned to the lender. The Portfolio may, without limitation, seek to obtain market exposure to the securities in which it primarily invests by entering into a series of purchase and sale contracts or by using other investment techniques (such as buy backs or dollar rolls).The “total return” sought by the Portfolio consists of income earned on the Portfolio’s investments, plus capital appreciation, if any, which generally arises from decreases in interest rates or improving credit fundamentals for a particular sector or security. The Portfolio may engage in frequent and active trading of portfolio securities to achieve its investment objective, particularly during periods of volatile market movements.The Portfolio’s investments in fixed income securities are limited to investment grade U.S. dollar denominated securities of U.S. issuers that are rated at least A by Moody’s or equivalently rated by S&P or Fitch, or, if unrated, determined by the adviser to be of comparable quality. If a downgrade in the rating of a security in which the Portfolio is invested causes it to fall outside these parameters, the adviser will sell the impacted security as soon as reasonably practicable. In addition, with respect to the Portfolio’s investments in fixed income securities that are not U.S. Government Securities, (and subject to the requirement that the Portfolio under normal circumstances maintains at least 80% of its net assets (plus any borrowing for investment purposes) in U.S. Government Securities) the Portfolio may only invest up to 10% of its total assets in securities rated A by Moody’s or equivalently rated by S&P or Fitch, or, if unrated, determined by the adviser to be of comparable quality, and may only invest up to 25% of its total assets in securities rated Aa by Moody’s or equivalently rated by S&P or Fitch or, if unrated, determined by the adviser to be of comparable quality.The Portfolio may sell a position when, in the adviser’s opinion, it no longer represents a good value, when a superior risk/return opportunity exists in a substitute position, or when it no longer fits within the Portfolio’s macroeconomic or structural strategy. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected and the adviser’s quality determinations with respect to securities that are unrated by the major credit rating agencies may be inaccurate, which could cause the Portfolio to underperform other mutual funds or lose money. •Counterparty Risk – The Portfolio may sustain a loss in the event the other party(s) in an agreement or a participant to a transaction, such as a broker or swap counterparty, defaults on a contract or fails to perform by failing to pay amounts due, failing to fulfill delivery conditions, or failing to otherwise comply with the terms of the contract. Counterparty risk is inherent in many transactions, including derivatives transactions. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security or the counterparty to a derivatives contract is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The Portfolio’s use of derivatives involves risks different from, or possibly greater than, the risks associated with investing directly in securities or other traditional investments. Investments in derivatives may not have the intended effects and may result in losses for the Portfolio that may not otherwise have occurred or missed opportunities for the Portfolio. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. The derivatives could involve management, credit, interest rate, liquidity and market risks, and the risks of misplacing or improper valuation. Changes in the value of the derivative may not correlate as intended with the underlying asset, rate or index. In addition, the Portfolio could sustain a loss in the event the counterparty to a derivatives transaction fails to make the required payments or otherwise comply with the terms of the contract. The Portfolio’s purchase of forwards and futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. In addition, the purchase of forwards also involves counterparty credit risk as well as heightened market risk. The Portfolio’s purchase of swap agreements may pose risk arising from losses if the underlying reference asset does not perform as anticipated; such agreements are also subject to counterparty credit, liquidity and leveraging risks. The Portfolio’s use of options involve risk related to the direction and timing of market movements in the price of the underlying asset, obligations related to exercise of the option, and potential loss in value of the initial investment. •Equity Securities Risk – The value of equity securities, such as common and preferred stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •High Portfolio Turnover Risk – Active and frequent trading may cause higher brokerage expenses and other transaction costs, which may adversely affect the Portfolio’s performance. •Inflation Risk – Your investment in the Portfolio may not provide enough income to keep pace with inflation. •Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments is likely to decline. A significant rise in interest rates over a short period of time could cause significant losses in the market value of the Portfolio’s fixed income instruments. A Portfolio with a longer average portfolio duration will be more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration. For example, the market value of a fixed income portfolio with an average duration of five years generally would be expected to fall approximately 5% if interest rates rose by one percentage point. Declining interest rates may increase the risk that an issuer calls outstanding securities prior to their maturity. •Issuer Risk – The risk that the value of a security may decline for a reason directly related to the issuer, such as management performance, financial leverage and reduced demand for the issuer’s goods or services. •Leverage Risk – Certain transactions, such as when issued, delayed delivery or forward commitments transactions, or the use of derivative transactions, may give rise to leverage, causing more volatility than if the Portfolio had not been leveraged. •Liquidity Risk – Fixed income and derivative investments can be difficult to purchase or sell at an advantageous time or price, if at all, during periods of reduced marketability for the investment or due to the size of the transaction. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mortgage- and Asset-Backed Securities Risk – The risks of investing in mortgage-related and other asset-backed securities, including interest rate risk, credit risk, liquidity risk, prepayment risk and extension risk. Mortgage-related and other asset-backed securities represent interests in pools of mortgages or other assets and often involve risks that are different or possibly more acute than risks associated with other types of debt instruments. The value of some mortgage- or asset-backed securities may be particularly sensitive to changes in prevailing interest rates. The use of mortgage dollar rolls involves potential risks of loss that are different from those related to the mortgage securities underlying the transactions, including counterparty risk, market risk, and financial risk (including the risk that the value of the principal and interest payments associated with the mortgage instrument sold to a counterparty exceeds the compensation paid to the Portfolio by the counterparty). •Preferred Stocks Risk – Preferred stocks often lack a fixed maturity or redemption date and are therefore more susceptible to price fluctuations when interest rates change. They also carry a greater risk of non-receipt of income because unlike interest on debt securities, dividends on preferred stocks must be declared by the issuer’s board of directors before becoming payable. •Prepayment and Extension Risk – Prepayment risk is the risk that principal on a debt obligation will be paid earlier than scheduled or expected, which could reduce yield and market value of the security and shorten the Portfolio’s average effective maturity. The rate of prepayments tends to increase as interest rates fall. Extension risk is the risk that, as interest rates rise, repayments on a debt obligation may occur more slowly than anticipated by the market and the obligation may remain outstanding longer. •Short Sale Risk – The risk of entering into short sales, including the potential loss of more money than the actual cost of the investment, and the risk that the third party to the short sale may fail to honor its contract terms, causing a loss to the Portfolio. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •U.S. Government Securities Risk – Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the Portfolio does not apply to the market value of such security or to shares of the Portfolio itself. •When Issued, Delayed Delivery and Forward Commitment Risk – When issued, delayed delivery purchases and forward commitment transactions involve a risk of loss if the value of the securities declines prior to the settlement date. This risk is in addition to the risk that the Portfolio’s other assets will decline in value. Therefore, these transactions may result in a form of leverage and increase the Portfolio’s overall investment expense. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter1st quarter, 202020.64%Worst Quarter1st quarter, 2021-13.26% Best Quarter 2020-03-31 0.2064 Worst Quarter 2021-03-31 -0.1326 Average Annual Total Return(for periods ended December 31, 2023) 0.0333 -0.0176 0.0181 0.0306 -0.0124 0.0228 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to pursue total return using a strategy that seeks to protect against U.S. inflation. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0053 0 0.0005 0.0058 -0.0014 0.0044 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio's operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 45 172 310 712 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 40.64% of the average value of its portfolio. 0.4064 PRINCIPAL INVESTMENT STRATEGIES The Portfolio invests substantially all of its assets in investment-grade debt securities. To help protect against U.S. inflation (as measured by the change in the Consumer Price Index over time), under normal conditions, the Portfolio will invest over 50% of its net assets (plus any borrowings for investment purposes) in inflation-indexed debt securities. These securities include inflation-indexed U.S. Treasury Securities, inflation-indexed securities issued by U.S. government agencies and instrumentalities other than the U.S. Treasury, and inflation-indexed securities issued by domestic and foreign corporations and governments, and may include those located in emerging markets. Inflation-indexed securities are designed to protect the future purchasing power of the money invested in them. The Portfolio also may invest in fixed income securities that are not inflation-indexed. Such investments may include other investment grade debt securities, including collateralized mortgage obligations, mortgage-backed securities, including commercial mortgage-backed securities and agency mortgage-backed securities, and asset-backed securities, including collateralized loan obligations, whether issued by the U.S. government, its agencies or instrumentalities, corporations or other non-governmental issuers, or foreign governments. Investment grade securities are generally securities rated investment grade by major credit rating agencies (BBB- or higher by S&P; Baa3 or higher by Moody’s; BBB- or higher by Fitch) or, if unrated, determined by the Portfolio’s adviser to be of comparable quality.Due to Internal Revenue Code provisions and regulations governing insurance product funds, no more than 55% of the Portfolio’s assets may be invested in securities issued by the same entity. Because the number of inflation-indexed debt securities issued by entities is limited, at times the Portfolio may have a substantial position in non-inflation-indexed securities. To seek to reduce the impact of this limitation, the adviser may purchase (long) inflation swap agreements to manage or reduce the risk of the effects of inflation with respect to the Portfolio’s position in non-inflation-indexed securities.The adviser is not limited to a specific weighted average maturity or duration range. However, the adviser monitors the Portfolio’s weighted average maturity and duration and seeks to adjust it as appropriate, taking into account market conditions, the current inflation rate and other relevant factors.The Portfolio may invest up to 20% of its total assets in securities denominated in foreign currencies and may invest beyond this limit in U.S. dollar denominated securities of foreign issuers. The Portfolio may hedge some or all of its foreign currency by utilizing forward foreign currency exchange contracts to seek to reduce the risk of loss due to fluctuations in the currency exchange rates. The Portfolio may also use interest rate futures to adjust overall interest rate exposure when the adviser deems it to be advantageous.The Portfolio may sell a security for a variety of reasons, including its assessment of the security’s relative attractiveness in light of its evaluation of current economic conditions or the risk of inflation, or to manage the Portfolio’s maturity and credit quality standards. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected and the adviser’s quality determinations with respect to securities that are unrated by the major credit rating agencies may be inaccurate, which could cause the Portfolio to underperform other mutual funds or lose money. •Counterparty Risk – The Portfolio may sustain a loss in the event the other party(s) in an agreement or a participant to a transaction, such as a broker or swap counterparty, defaults on a contract or fails to perform by failing to pay amounts due, failing to fulfill delivery conditions, or failing to otherwise comply with the terms of the contract. Counterparty risk is inherent in many transactions, including derivatives transactions. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Debt Obligations of Foreign Governments Risk – The issuer of the foreign debt or the governmental authorities that control the repayment of such debt may be unable or unwilling to repay principal or interest when due, and the Portfolio may have limited recourse in the event of a default. The market prices of debt obligations of governments and their agencies, and the Portfolio’s net asset value, may be more volatile than prices of U.S. debt obligations. In addition, unlike debt instruments issued by the U.S. Treasury, inflation-linked bonds issued by corporations or foreign governments do not generally provide principal protection, and in a deflationary environment, such bonds may result in the loss of principal. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that the counterparty to a derivatives transaction fails to make the required payment or otherwise comply with the terms of the contract, the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index, and the risk of adverse price movements in the market. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include management, interest rate, liquidity risks and the risk of missed opportunities in other investments. The Portfolio's purchase of swap agreements may pose risk arising from losses if the underlying reference asset does not perform as anticipated; such agreements are also subject to counterparty credit, liquidity and leveraging risks. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar, or in the case of hedged positions, that the U.S. dollar will decline in value relative to the currency being hedged, and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Inflation Risk – Your investment in the Portfolio may not provide enough income to keep pace with inflation. To the extent that the Portfolio holds investments in non-inflation-linked debt securities, as noted above, that portion of the Portfolio will not be automatically protected from inflation. •Interest Rate Risk – Prices of fixed income instruments, including inflation-indexed debt securities, generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments is likely to decline. A significant rise in interest rates over a short period of time could cause significant losses in the market value of the Portfolio's fixed income instruments. A portfolio with a longer average portfolio duration will be more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration. For example, the market value of a fixed income portfolio with an average duration of five years generally would be expected to fall approximately 5% if interest rates rose by one percentage point. Declining interest rates may increase the risk that an issuer calls outstanding securities prior to their maturity. •Liquidity Risk – Fixed income and derivative investments can be difficult to purchase or sell at an advantageous time or price, if at all, during periods of reduced marketability for the investment or due to the size of the transaction. These risks may be magnified during periods of economic turmoil or in an extended economic downturn or when investing in emerging markets. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mortgage- and Asset-Backed Securities Risk – The Portfolio invests in collateralized mortgage obligations, mortgage-backed securities, including commercial mortgage-backed securities, collateralized loan obligations, and asset-backed securities. Mortgage-related and other asset-backed securities are subject to interest rate risk, credit risk and liquidity risk as well as additional risks including prepayment and extension risk. Mortgage-related and other asset-backed securities represent interests in pools of mortgages or other assets and often involve risks that are different or possibly more acute than risks associated with other types of debt instruments. The value of some mortgage- or asset-backed securities may be particularly sensitive to changes in prevailing interest rates. Mortgage-backed securities offered by non-governmental issuers are subject to specific risks, such as the failure of private insurers to meet their obligations and unexpectedly high rates of default on the mortgages backing the securities. Other asset-backed securities are subject to risks similar to those associated with mortgage-backed securities, as well as risks associated with the nature and servicing of the assets underlying the securities. Asset-backed securities may not have the benefit of a security interest in collateral comparable to that of mortgage assets, resulting in additional credit risk. •Prepayment and Extension Risk – Prepayment risk is the risk that principal on a debt obligation will be paid earlier than scheduled or expected, which could reduce yield and market value of the security and shorten the Portfolio’s average effective maturity. The rate of prepayments tends to increase as interest rates fall. Extension risk is the risk that, as interest rates rise, repayments on a debt obligation may occur more slowly than anticipated by the market and the obligation may remain outstanding longer. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •U.S. Government Securities Risk – Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the Portfolio does not apply to the market value of such security or to shares of the Portfolio itself. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 20206.08%Worst Quarter2nd quarter, 2022-6.94% Best Quarter 2020-06-30 0.0608 Worst Quarter 2022-06-30 -0.0694 Average Annual Total Return(for periods ended December 31, 2023) 0.0390 0.0286 0.0206 0.0390 0.0315 0.0242 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to achieve high current income and capital appreciation. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0042 0 0.0004 0.0046 Restated to reflect current expenses. Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 47 148 258 579 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 17.2% of the average value of its portfolio. PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio invests at least 80% of net assets (plus any borrowings for investment purposes) in non-investment grade debt securities. Non-investment grade securities are generally securities rated below investment grade by major credit rating agencies (BB+ or lower by S&P; Ba1 or lower by Moody’s; BB+ or lower by Fitch), or, if unrated, determined by the Portfolio’s adviser to be of comparable quality. There is no minimal acceptable rating for a security to be purchased or held by the Portfolio. The Portfolio may invest up to 30% of net assets in non-investment grade foreign securities, including those of issuers located in emerging markets, consistent with its investment objective. Foreign securities held by the Portfolio consist primarily of U.S. dollar denominated securities but may also include non-U.S. dollar denominated securities.The securities in which the Portfolio primarily invests are considered speculative and are sometimes known as “junk bonds.” These securities tend to offer higher yields than higher rated securities of comparable maturities primarily because of the market’s greater uncertainty about the issuer’s ability to make all required interest and principal payments, and therefore about the returns that will in fact be realized by the Portfolio.The adviser selects securities that it believes have attractive investment characteristics and seeks to minimize default risk and other risks through careful security selection and diversification. The adviser’s securities selection process consists of a credit-intensive, fundamental analysis of the issuer. The adviser’s analysis focuses on the issuer’s financial condition, business and product strength, competitive position and management expertise. Further, the adviser considers current economic, financial market and industry factors, which may affect the issuer. The adviser does not limit the Portfolio’s investments to securities of a particular maturity range and does not target an average effective maturity or duration.In addition, as part of its security selection process, among other factors, the adviser also evaluates whether environmental, social and governance factors could have positive or negative impact on the risk profiles of many issuers in the universe of securities in which the Portfolio may invest. Examples of ESG factors that may be considered include, but are not limited to, carbon emissions, waste and harmful substance management, product and employee safety, human capital management and labor relations, and corporate governance structure and oversight. Specific factors and the weight given to those factors will vary relative to the material impact it may have on the risk assessment of the issuer. The adviser may also consider information derived from active engagement conducted by its in-house stewardship team with certain issuers or guarantors. This qualitative analysis does not automatically result in including or excluding specific securities but may be used by the adviser as an additional input to Portfolio risk/return characteristics. Consideration of ESG factors may not be determinative in the adviser’s investment process and the adviser may conclude that other attributes of an investment outweigh ESG considerations when making investment decisions for the Portfolio.The adviser strives to adhere to a strong sell discipline and generally effects a sale if it believes a security’s future total return has become less attractive relative to other securities, the company begins to perform poorly, the industry outlook changes, or any other event occurs that changes the adviser’s conclusion. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected and the adviser's quality determinations with respect to securities that are unrated by the major credit rating agencies may be inaccurate, which could cause the Portfolio to underperform other mutual funds or lose money. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •ESG Risk – Incorporating the consideration of ESG factors in the investment process may result in the exclusion of certain securities for non-investment reasons and therefore the Portfolio may forego some market opportunities available to funds that do not consider ESG factors. The evaluation of ESG factors may affect the Portfolio’s exposure to certain issuers or industries and may not work as intended. The Portfolio may underperform other funds that do not consider ESG factors or that use different ESG factors to evaluate a security. Information used to evaluate ESG factors may not be readily available, complete, or accurate, and may vary across providers and issuers, as ESG factors are not uniformly defined or assessed. There is no guarantee that evaluating ESG considerations for individual securities will positively contribute to the Portfolio’s performance results. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar, or in the case of hedged positions, that the U.S. dollar will decline in value relative to the currency being hedged, and may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio’s investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •High Yield Debt Risk – High yield debt securities (so called “junk bonds”) in which the Portfolio invests have greater interest rate and credit risk, may be more difficult to sell or sell at a reasonable price, have greater risk of loss than higher rated securities, and are predominantly speculative with respect to an issuer’s ability to pay interest and repay principal. In addition, high yield debt securities may be particularly sensitive to changes in the securities markets. •Inflation Risk – Your investment in the Portfolio may not provide enough income to keep pace with inflation. •Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments is likely to decline. A significant rise in interest rates over a short period of time could cause significant losses in the market value of the Portfolio’s fixed income instruments. Duration measures the price sensitivity of a fixed income instrument to changes in interest rates. A portfolio with a longer average portfolio duration will be more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration. For example, the market value of a fixed income portfolio with an average duration of five years generally would be expected to fall approximately 5% if interest rates rose by one percentage point. Declining interest rates may increase the risk that an issuer calls outstanding securities prior to their maturity. •Liquidity Risk – High yield debt securities may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn or when investing in emerging markets. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202010.08%Worst Quarter1st quarter, 2020-12.32% Best Quarter 2020-06-30 0.1008 Worst Quarter 2020-03-31 -0.1232 Average Annual Total Return(for periods ended December 31, 2023) 0.1324 0.0533 0.0442 0.1344 0.0535 0.0459 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to seek maximum total return, consistent with prudent investment management. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0077 0 0.0006 0.0083 -0.0010 0.0073 April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio's operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 75 255 451 1016 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 26.41% of the average value of its portfolio. 0.2641 PRINCIPAL INVESTMENT STRATEGIES Normally, the Portfolio seeks to achieve its investment objective by investing at least 80% of its net assets (plus any borrowings for investment purposes) in a diversified portfolio of fixed income instruments of varying maturities, which may be represented by forwards or derivatives such as options, futures contracts or swap agreements, including the purchase or sale of credit default swaps, and interest rate swaps (to take a position on interest rates moving either up or down). The average portfolio duration of the Portfolio normally varies from three to eight years, based on the adviser’s forecast for interest rates. Duration is a measure of the sensitivity of the price of the Portfolio’s fixed income securities to changes in interest rates; the longer the duration, the more sensitive the price will be to changes in interest rates.The Portfolio may invest all of its assets in high yield securities subject to a maximum of 10% of its total assets in securities rated below B by Moody’s or equivalently rated by S&P or Fitch or, if unrated, determined by the Portfolio’s adviser to be of comparable quality. High yield securities, commonly referred to as “junk” bonds, are non-investment grade securities. A security is considered to be non-investment grade when it is rated below investment grade by at least two of the three credit ratings agencies (BB+ or lower by S&P; Ba1 or lower by Moody’s; BB+ or lower by Fitch) or if unrated, determined by the Portfolio’s adviser to be of comparable quality. The Portfolio may invest, without limitation, in securities denominated in foreign currencies and U.S. dollar denominated securities of foreign issuers. In addition, the Portfolio may invest without limit in fixed income securities of issuers that are economically tied to emerging securities markets. The Portfolio may invest in illiquid securities. The Portfolio may also invest up to 10% of its net assets in preferred stocks.The Portfolio may invest all of its assets in derivative instruments, such as options, futures contracts or swap agreements including the purchase or sale of credit defaults swaps, and interest rate swaps (to take a position on interest rates moving either up or down), in municipal bonds, contingent convertible securities, or in mortgage- or asset-backed securities, subject to the Portfolio’s objective and policies. The Portfolio may utilize currency forwards and currency options to manage or hedge currency exposure. The Portfolio may invest in mortgage- or asset-backed securities which are non-investment grade. Mortgage-backed securities may include residential and commercial mortgage-backed securities issued by a Federal agency and private label residential and commercial mortgage-backed securities. The adviser may invest in derivatives at any time it deems appropriate, generally when relative value and liquidity conditions make these investments more attractive relative to cash bonds.The Portfolio may purchase or sell securities on a when-issued, delayed delivery or forward commitment basis and may engage in short sales. A short sale involves the sale of a security that is borrowed from a broker or other institution, and which must be purchased in the market at a later date and returned to the lender. The Portfolio may, without limitation, seek to obtain market exposure to the securities in which it primarily invests by entering into a series of purchase and sale contracts or by using other investment techniques (such as buy backs or dollar rolls). The Portfolio may invest up to 10% of its net assets in fixed- and floating-rate loans, including senior loans, and such investments may be in the form of loan participations and assignments. Senior loans are considered speculative instruments.The “total return” sought by the Portfolio consists of income earned on the Portfolio’s investments, plus capital appreciation, if any, which generally arises from a decrease in interest rates or improving credit fundamentals for a particular sector or security. The Portfolio may engage in frequent and active trading of portfolio securities to achieve its investment objective, particularly during periods of volatile market movements.In selecting securities for a Portfolio, the adviser develops an outlook for interest rates, foreign currency exchange rates and the economy, analyzes credit and call risks, which involves both macro and fundamental analysis. The proportion of a Portfolio’s assets committed to investment in securities with particular characteristics (such as quality, sector, interest rate or maturity) varies based on the adviser’s outlook for the U.S. and foreign economies, the financial markets and other factors.The adviser attempts to identify areas of the bond market that are undervalued relative to the rest of the market. The adviser identifies these areas by grouping bonds into the following sectors: money markets, governments, corporates, mortgages, asset-backed and international. Sophisticated proprietary software then assists in evaluating sectors and pricing specific securities. Once investment opportunities are identified, the adviser will shift assets among sectors depending upon changes in relative valuations and credit spreads.The Portfolio may sell a position when, in the adviser’s opinion, it no longer represents a good value, when a superior risk/return opportunity exists in a substitute position, or when it no longer fits within the Portfolio’s macroeconomic or structural strategy. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected and the adviser’s quality determinations with respect to securities that are unrated by the major credit rating agencies may be inaccurate, which could cause the Portfolio to underperform other mutual funds or lose money. •Contingent Convertible Securities Risk – Investing in convertible contingent securities may subject the Portfolio to the risk of the occurrence of a triggering event which, depending on the underlying circumstances, may result in the issuer converting the security to an equity interest or writing down the principal value of such securities (either partially or in full). In addition, coupons associated with contingent convertible securities are typically fully discretionary, and coupon payments can be deferred or cancelled by the issuer without causing an event of default. •Convertible Securities Risk – Convertible securities (which can be bonds, notes, debentures, preferred stock, or other securities which are convertible into or exercisable for common stock), are subject to both the credit and interest rate risks associated with fixed income securities and to the stock market risk associated with equity securities. The value of a convertible security may not increase or decrease as rapidly as the underlying common stock. The Portfolio may be forced to convert a security before it would otherwise choose, which may have an adverse effect on the Portfolio’s ability to achieve its investment objective. •Counterparty Risk – The Portfolio may sustain a loss in the event the other party(s) in an agreement or a participant to a transaction, such as a broker or swap counterparty, defaults on a contract or fails to perform by failing to pay amounts due, failing to fulfill delivery conditions, or failing to otherwise comply with the terms of the contract. Counterparty risk is inherent in many transactions, including derivatives transactions. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Debt Obligations of Foreign Governments Risk – The issuer of the foreign debt or the governmental authorities that control the repayment of such debt may be unable or unwilling to repay principal or interest when due, and the Portfolio may have limited recourse in the event of a default. The market prices of debt obligations of governments and their agencies, and the Portfolio’s net asset value, may be more volatile than prices of U.S. debt obligations. •Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The Portfolio’s use of derivatives involves risks different from, or possibly greater than, the risks associated with investing directly in securities or other traditional investments. Investments in derivatives may not have the intended effects and may result in losses for the Portfolio that may not otherwise have occurred or missed opportunities for the Portfolio. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. The derivatives could involve management, credit, interest rate, liquidity and market risks, and the risks of misplacing or improper valuation. Changes in the value of the derivative may not correlate as intended with the underlying asset, rate or index. In addition, the Portfolio could sustain a loss in the event the counterparty to a derivatives transaction fails to make the required payments or otherwise comply with the terms of the contract. The Portfolio’s purchase of forwards and futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. In addition, the purchase of forwards also involves counterparty credit risk as well as heightened market risk. The Portfolio’s purchase of total return equity swap agreements may pose risk arising from losses if the underlying reference asset does not perform as anticipated; such agreements are also subject to counterparty credit, liquidity and leveraging risks. The Portfolio’s use of options involve risk related to the direction and timing of market movements in the price of the underlying asset, obligations related to exercise of the option, and potential loss in value of the initial investment. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities, such as common and preferred stocks, could decline if the financial condition of the companies the Portfolio is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Foreign Currency Risk – The risk that foreign (non-U.S. dollar) currency denominated securities, or derivatives that provide exposure to foreign currencies, may be adversely affected by decreases in foreign currency values relative to the U.S. dollar, or, in the case of hedged positions, that the U.S. dollar will decline in value relative to the currency being hedged. Investments in securities subject to foreign currency risk may have more rapid and extreme changes in value or more losses than investments in U.S. dollar denominated securities. •Foreign Investing Risk – Investing in foreign securities may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Investments in emerging markets impose risks different from, and greater than, investments in developed markets. Foreign securities may be less liquid, more volatile, and harder to value than U.S. securities. The Portfolio's investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •High Portfolio Turnover Risk – Active and frequent trading may cause higher brokerage expenses and other transaction costs, which may adversely affect the Portfolio’s performance. •High Yield Debt Risk – High yield debt securities (so called “junk bonds”) in which the Portfolio invests have greater interest rate and credit risk, may be more difficult to sell or sell at a reasonable price, have greater risk of loss than higher rated securities, and are predominantly speculative with respect to an issuer’s ability to pay interest and repay principal. In addition, high yield debt securities may be particularly sensitive to changes in the securities markets. •Inflation Risk – Your investment in the Portfolio may not provide enough income to keep pace with inflation. •Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments is likely to decline. A significant rise in interest rates over a short period of time could cause significant losses in the market value of the Portfolio’s fixed income instruments. A portfolio with a longer average portfolio duration will be more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration. For example, the market value of a fixed income portfolio with an average duration of five years generally would be expected to fall approximately 5% if interest rates rose by one percentage point. Declining interest rates may increase the risk that an issuer calls outstanding securities prior to their maturity. •Issuer Risk – The risk that the value of a security may decline for a reason directly related to the issuer, such as management performance, financial leverage and reduced demand for the issuer’s goods or services. •Leverage Risk – Certain transactions, such as when issued, delayed delivery or forward commitments transactions, or the use of derivative transactions, may give rise to leverage, causing more volatility than if the Portfolio had not been leveraged. •LIBOR Transition Risk – The risk related to the discontinuation of the London Interbank Offered Rate (“LIBOR”). Certain instruments held by the Portfolio may utilize LIBOR as their reference or benchmark rate. LIBOR had been used extensively in the U.S. and globally as the reference rate for various commercial and financial contracts, including corporate and municipal bonds and loans, floating rate mortgages, asset-backed securities, consumer loans, and derivatives. Although the transition process away from LIBOR for most instruments has been completed as of June 30, 2023, some LIBOR use is continuing and there may be potential effects related to the continued use of LIBOR on the Portfolio or on certain instruments in which the Portfolio invests. The continued transition process may involve, among other things, increased volatility or illiquidity in markets for instruments that currently rely on LIBOR and may result in a reduction in value of certain instruments held by the Portfolio. •Loan Risk – The risks associated with investing in fixed- and floating-rate loans, including senior loans, through loan participations and assignments or otherwise, can include credit risk, interest rate risk, liquidity risk, call risk, settlement risk, and risks associated with being a lender. With respect to senior loans, there may also be heightened credit risk to the extent such loans are below investment grade and made to less creditworthy companies. Senior loans that are considered to be “covenant-lite” offer less protection to the loan holder and may have increased credit risk and call risk. •Liquidity Risk – Fixed income and derivative investments can be difficult to purchase or sell at an advantageous time or price, if at all, during periods of reduced marketability for the investment or due to the size of the transaction. These risks may be magnified during periods of economic turmoil or in an extended economic downturn or when investing in emerging markets. •Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Mortgage- and Asset-Backed Securities Risk – The risks of investing in mortgage-related and other asset-backed securities, including interest rate risk, credit risk, liquidity risk, prepayment risk and extension risk. Privately-issued mortgage-backed securities carry a heightened risk of nonpayment because there are no direct or indirect government or agency guarantees of payments. The use of mortgage dollar rolls involves potential risks of loss that are different from those related to the mortgage securities underlying the transactions, including counterparty risk, market risk, and financial risk (including the risk that the value of the principal and interest payments associated with the mortgage instrument sold to a counterparty exceeds the compensation paid to the Portfolio by the counterparty). Asset-backed securities are subject to risks similar to those associated with mortgage-backed securities, as well as risks associated with the nature and servicing of the assets underlying the securities. Asset-backed securities may not have the benefit of a security interest in collateral comparable to that of mortgage assets, resulting in additional credit risk. Investments in mortgage-related and other asset-backed securities that are non-investment grade may have heightened liquidity risk. •Municipal Securities Risk – The value of municipal securities in which the Portfolio invests may be more sensitive to certain adverse conditions than other fixed income securities and the yields of municipal securities may move differently and adversely compared to the yields of the overall debt securities markets. Certain municipal securities may be or become highly illiquid. Illiquidity may be exacerbated from time to time by market or economic events. Municipal securities may lose their tax-exempt status if certain legal requirements are not met, or if federal or state tax laws change. The Portfolio’s investments in certain municipal securities with principal and interest payments that are made from the revenues of a specific project or facility, and not general tax revenues, may have increased risks. •Preferred Stocks Risk – Preferred stocks often lack a fixed maturity or redemption date and are therefore more susceptible to price fluctuations when interest rates change. They also carry a greater risk of non-receipt of income because unlike interest on debt securities, dividends on preferred stocks must be declared by the issuer’s board of directors before becoming payable. •Prepayment and Extension Risk – Prepayment risk is the risk that principal on a debt obligation will be paid earlier than scheduled or expected, which could reduce yield and market value of the security and shorten the Portfolio’s average effective maturity. The rate of prepayments tends to increase as interest rates fall. Extension risk is the risk that, as interest rates rise, repayments on a debt obligation may occur more slowly than anticipated by the market and the obligation may remain outstanding longer. •Short Sale Risk – The risk of entering into short sales, including the potential loss of more money than the actual cost of the investment, and the risk that the third party to the short sale may fail to honor its contract terms, causing a loss to the Portfolio. •Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so. •U.S. Government Securities Risk – Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the Portfolio does not apply to the market value of such security or to shares of the Portfolio itself. •When Issued, Delayed Delivery and Forward Commitment Risk – When issued, delayed delivery purchases and forward commitment transactions involve a risk of loss if the value of the securities declines prior to the settlement date. This risk is in addition to the risk that the Portfolio’s other assets will decline in value. Therefore, these transactions may result in a form of leverage and increase the Portfolio’s overall investment expense. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance and the returns of an equally weighted blend of certain indices of securities with characteristics similar to those that the Portfolio typically holds.Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance and the returns of an equally weighted blend of certain indices of securities with characteristics similar to those that the Portfolio typically holds. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202010.18%Worst Quarter1st quarter, 2020-10.35% Best Quarter 2020-06-30 0.1018 Worst Quarter 2020-03-31 -0.1035 Average Annual Total Return(for periods ended December 31, 2023) 0.0971 0.0234 0.0302 0.0936 0.0251 0.0311 0.1084 0.0319 0.0360 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to realize as high a level of total return as is consistent with prudent investment risk, through income and capital appreciation. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0030 0 0.0001 0.0039 0.0070 -0.0020 0.0050 Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio's operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 51 204 370 852 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 9.19% of the average value of its portfolio. 0.0919 PRINCIPAL INVESTMENT STRATEGIES Investing in multiple investment asset classes, the Portfolio attempts to capitalize on the variation in return potential produced by the interaction of changing financial markets and economic conditions while maintaining a balance over time between investment opportunities and their associated potential risks by following a flexible policy of allocating assets.The Portfolio is tactically and strategically managed to capitalize on changing financial markets and economic conditions following a flexible policy for allocating assets utilizing the following strategic asset class target ranges:Equity and Other* ExposureFixed Income or Debt ExposureCash Equivalents40 – 60%40 – 60%0 – 10%*Other exposure includes REIT and commodity-related investments.These foregoing percentage target ranges are not intended to establish minimum and maximum limits. The adviser may deviate from the asset class target ranges in pursuit of total return and in response to changing market and economic conditions, and, may invest a greater or lesser percentage in any strategic asset class component when the adviser deems it favorable to do so in order to achieve the Portfolio’s investment objective.The Portfolio operates primarily as a “fund of funds” to gain the Portfolio’s multi-asset class exposure. The fund may invest in underlying Portfolios of Northwestern Mutual Series Fund, Inc. (each, an “Underlying Portfolio”) and exchange-traded funds (“ETFs”) which are not portfolios of Northwestern Mutual Series Fund, Inc. The Portfolio may obtain equity exposure by investing in one or more of the domestic or international Underlying Portfolios or ETFs and may obtain fixed income exposure by investing in one or more of the fixed income Underlying Portfolios or ETFs. The cash equivalent portion of the Portfolio may include, but is not limited to, ETFs, investment in debt securities issued or guaranteed by the U.S. government or its agencies or instrumentalities, including mortgage- and asset-backed securities, as well as commercial paper, banker’s acceptances, certificates of deposit and time deposits. In order to enhance short duration returns, the adviser may purchase ultra-short bond ETFs. For purposes of the strategic asset class ranges utilized herein, the adviser includes these instruments in the Cash Equivalents asset class together with cash and cash equivalent instruments. The Portfolio may also invest in ETFs that invest in real estate investment trusts (REITs). The Portfolio may invest in commodities through the purchase of swaps on physical commodities or commodity indices, including those which are traded in over-the-counter markets (“OTC”). The Portfolio may also invest in ETFs for purposes of obtaining exposure to commodities markets. The adviser allocates the Portfolio’s assets among the Underlying Portfolios and ETFs based on the adviser’s economic and market outlook and the investment objectives and strategies of the Underlying Portfolios and ETFs. With respect to the equity and international Underlying Portfolios and ETFs, the adviser considers their investment focus on small, mid or large market capitalizations, domestic or foreign investments, whether the Underlying Portfolio or ETF is diversified or non-diversified and whether it employs a “growth” or “value” style of investing, among other characteristics. With respect to fixed income Underlying Portfolios and ETFs, the adviser considers their focus on investment grade or non-investment grade securities, domestic or foreign investments, whether the issuer is a government or government agency, the duration (that is, a measure of the sensitivity to changes in interest rates) and maturity of the Underlying Portfolio or ETF, and other characteristics. The adviser regularly reviews and adjusts the allocation among the Underlying Portfolios and ETFs to favor investments in those Underlying Portfolios and ETFs that the adviser believes provide the most favorable position for achieving the Portfolio’s investment objective. In connection with the allocation process, the Portfolio may invest more than 25% of its assets in one Underlying Portfolio or one ETF.Through its investments in the equity and international Underlying Portfolios and ETFs, the Portfolio may be exposed to a wide range of equity securities and other instruments, including small, mid and large cap U.S. and non-U.S. stocks. Equity securities could include common and preferred stocks, securities convertible into stocks and depositary receipts for those securities. Through its investments in the fixed income Underlying Portfolios and ETFs, the Portfolio may be exposed to a wide range of fixed income securities with varying durations and maturities, including investment grade and non-investment grade debt securities, debt of corporate and government issuers, inflation-indexed debt securities, and other fixed income instruments. The Fund considers a fixed income security to be investment grade if the security is rated investment grade by at least two of the three credit rating agencies (BBB- or higher by S&P; Baa3 or higher by Moody’s; BBB- or higher by Fitch) and a security to be non-investment grade if the security is rated below investment grade by at least two of the three credit ratings agencies (BB+ or lower by S&P; Ba1 or lower by Moody’s; BB+ or lower by Fitch). An Underlying Portfolio or ETF may invest a large percentage of its assets in a single issuer, security, market or sector (or a limited group thereof) or in the case of an international Underlying Portfolio or ETF, may invest in emerging markets, a small number of countries or a particular geographic region. An Underlying Portfolio or ETF may also use certain derivative instruments including futures, forwards, options and swaps to meet its investment objective and for cash management purposes.When the adviser deems it to be more efficient or advantageous in managing the Portfolio, the adviser may utilize futures, options, forwards and swap agreements (including the purchase and sale of total return equity swaps and credit default swaps) to gain additional exposure to certain markets, sectors, regions or commodities, as alternatives to investments in Underlying Portfolios or ETFs, to adjust the Portfolio for the adviser’s view on style or term structure and duration, to provide increased flexibility in asset allocation, to earn income and to otherwise seek to enhance returns or to hedge foreign currency exposure.The Portfolio is designed primarily for investors who want their investment allocated across major asset classes while pursuing the growth potential of equities, but who also want the income potential of bonds. The investor should be willing to accept fluctuation in share prices that are typical for a portfolio that holds equity investments. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •Affiliated Portfolio Risk – In managing the Portfolio, the adviser has the authority to select, and allocate among, Underlying Portfolios. The adviser may be subject to potential conflicts of interest in selecting Underlying Portfolios because the fees paid to it by some Underlying Portfolios are higher than the fees paid by other Underlying Portfolios. Moreover, a situation could occur where proper action for the Portfolio could be adverse to the interest of the Underlying Portfolios or vice versa. •Asset Allocation Risk – This Portfolio allocates its investments among multiple investment asset classes and among Underlying Portfolios and ETFs, based upon judgments made by the adviser. The Portfolio could miss attractive investment opportunities by underweighting markets or sectors where there are significant returns, and could lose value by overweighting markets where there are significant declines, or may not correctly predict the times to shift assets from one type of investment to another. •Commodities Risk – The Portfolio’s investments in ETFs and total return swaps whose performance is linked to the price of an underlying commodity or commodity index may be subject to the risks of investing in physical commodities, including risks posed by regulatory, economic and political developments, weather events, natural disasters and market disruption. Commodity prices may have greater volatility than investments in traditional securities.•Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index, the risk of adverse price movements in the market, the risk of missed opportunities in other investments and the risk that the counterparty to a derivatives transaction fails to make the required payment or otherwise comply with the terms of the contract. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include management, interest rate and liquidity risks. The Portfolio’s purchase of forwards and futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. In addition, the purchase of forwards also involves counterparty credit risk as well as heightened market risk. The Portfolio’s purchase of total return equity swap agreements and total return commodities swap agreements may pose risk arising from losses if the underlying reference asset does not perform as anticipated; such agreements are also subject to counterparty credit, liquidity and leveraging risks. The Portfolio’s use of options involve risk related to the direction and timing of market movements in the price of the underlying asset, obligations related to exercise of the option, and potential loss in value of the initial investment. •Convertible Securities Risk – Convertible securities (which can be bonds, notes, debentures, preferred stock, or other securities which are convertible into or exercisable for common stock), are subject to both the credit and interest rate risks associated with fixed income securities and to the stock market risk associated with equity securities. The value of a convertible security may not increase or decrease as rapidly as the underlying common stock. The Portfolio may be forced to convert a security before it would otherwise choose, which may have an adverse effect on the Portfolio’s ability to achieve its investment objective. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security held directly or through an Underlying Portfolio or ETF is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities held through the Underlying Portfolios and ETFs, such as common and preferred stocks, could decline if the financial condition of the companies an Underlying Portfolio or ETF is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Exchange Traded Funds Risk – Investing in exchange traded funds (ETFs) may expose the Portfolio to greater risk of loss and price fluctuation than investing directly in a comparable portfolio of stocks comprising the index due to lack of liquidity, the additional expenses incurred as a shareholder in another investment company, and tracking error. ETFs are also subject to the risk that their market prices may trade at a premium or discount to their net asset value, which means the Portfolio will overpay for an ETF’s assets if it is trading at a premium and will get less than the value of the ETF’s assets when selling if it is trading at a discount. An active market for an ETF may not be developed or maintained. Trading of an ETF’s shares may be halted by the exchange, in which case the Portfolio would be unable to sell its ETF shares unless and until trading is resumed. Investing in ultra-short bond ETFs may pose greater risk than investments in cash equivalents such as money market mutual funds, including risks associated with the credit quality, duration and interest rate sensitivity of the bond instruments held within such ETFs. Ultra-short bond ETFs may be more volatile and involve greater credit and interest rate risk than money market funds and other cash equivalents. In addition, the price of an ultra-short bond ETF may fluctuate, while the goal of a money market mutual fund is to maintain its NAV at a stable $1 per share. Ultra-short bond ETFs may lose money despite a stated investment objective of returning capital. •Foreign Investing Risk – Exposure to investments in foreign securities, including through Underlying Portfolios and ETFs, may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. Exposure to investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Fund of Funds Investing Risk – The Portfolio’s investment performance is significantly impacted by the investment performance of the Underlying Portfolios and ETFs it holds. The ability of the Portfolio to meet its investment objective is related to the ability of the Underlying Portfolios or ETFs to meet their respective investment objectives as well as the adviser’s allocation decisions with respect to the Underlying Portfolios and ETFs. Each of the Underlying Portfolios and ETFs has its own investment risks, and the Portfolio is indirectly exposed to all the risks of the Underlying Portfolios and ETFs in direct proportion to the amount of assets the Portfolio allocates to each Underlying Portfolio and each ETF. To the extent that the Portfolio invests a significant portion of its assets in a single Underlying Portfolio or ETF, it will be particularly sensitive to the risks associated with that Underlying Portfolio or ETF. Changes in the value of that Underlying Portfolio or ETF may have a significant effect on the Portfolio’s net asset value. The Portfolio will bear a pro rata share of the Underlying Portfolios’ or ETFs’ expenses. •Geographic Focus Risk – The Portfolio’s performance could be more volatile than that of a more geographically diversified fund and could be significantly impacted as a result of the Portfolio investing a relatively large percentage of its assets in issuers located in a single country, a small number of countries, or a particular geographic region. Also, the Portfolio’s performance may be more closely tied to the market, currency, economic, political, or regulatory conditions in those countries or that region. Similarly, the extent to which an Underlying Portfolio or ETF invests a significant portion of its assets in a single country, a small number of countries or a particular geographic region, may also adversely impact the Portfolio, depending on the Portfolio’s level of investment in that Underlying Portfolio or ETF. •High Yield Debt Risk – High yield debt securities (so called “junk bonds”) in which the Portfolio has exposure have greater interest rate and credit risk, may be more difficult to sell or sell at a reasonable price, have greater risk of loss than higher rated securities, and are predominantly speculative with respect to an issuer’s ability to pay interest and repay principal. In addition, high yield debt securities may be particularly sensitive to changes in the securities markets. •Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments to which the Portfolio has exposure is likely to decline. A significant rise in interest rates over a short period of time could cause significant losses in the market value of the Portfolio’s fixed income instruments. Duration measures the price sensitivity of a fixed income instrument to changes in interest rates. The Portfolio’s exposure to fixed income instruments and Underlying Portfolios or ETFs with a longer average portfolio duration will be more sensitive to changes in interest rates than those with a shorter average duration. •Investment Style Risk – The Portfolio is subject to risks associated with an Underlying Portfolio’s or ETF's particular style of investing, such as growth or value or a combination of both, and may underperform with respect to its allocation to the Underlying Portfolio or ETF when the market does not favor that particular investment style. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Exposure to investments in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Large Transaction Risk – The Underlying Portfolios are used as investments for certain fund of funds, including the Portfolio, and may have a large percentage of their shares owned by such funds. Large redemption activity by the Portfolio or another fund of funds could result in the Underlying Portfolio being forced to sell portfolio securities at a loss to meet redemptions. The adviser may coordinate directly with the portfolio managers of the Underlying Portfolios to attempt to ensure that transactions are accommodated efficiently, including possibly implementing trades over a period of days rather than all at once. These practices may temporarily affect the adviser’s ability to fully implement the Portfolio’s investment strategies. •Liquidity Risk – Particular investments, such as small and micro cap stocks, fixed income securities, foreign securities, in particular emerging markets securities, and derivatives to which the Portfolio has exposure, can be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio or an Underlying Portfolio or ETF in which the Portfolio invests may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Micro Cap Company Risk – Exposure to investments in micro cap stocks may cause the Portfolio to experience more rapid and extreme changes in value than a fund that invests solely in small, mid and large cap stocks due to a more limited track record, narrower product markets, more limited resources, higher risk of failure, and less liquid trading markets. •Mortgage- and Asset-Backed Securities Risk – The risks of investing in mortgage-related and other asset-backed securities, including interest rate risk, credit risk, liquidity risk, extension risk and prepayment risk. Mortgage-related and other asset-backed securities represent interests in pools of mortgages or other assets and often involve risks that are different or possibly more acute than risks associated with other types of debt instruments. The value of some mortgage- or asset-backed securities may be particularly sensitive to changes in prevailing interest rates. •Preferred Stocks Risk – Preferred stocks often lack a fixed maturity or redemption date and are therefore more susceptible to price fluctuations when interest rates change. They also carry a greater risk of non-receipt of income because unlike interest on debt securities, dividends on preferred stocks must be declared by the issuer’s board of directors before becoming payable. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests in Underlying Portfolios or ETFs with a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio invests in Underlying Portfolios or ETFs that are underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Small and Mid Cap Company Risk – Exposure to investments in small and mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •U.S. Government Securities Risk – Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the Portfolio does not apply to the market value of such security or to shares of the Portfolio itself. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance for both equity and fixed income securities and the returns of a composite of indices of securities with characteristics similar to those the Portfolio typically holds.Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance for both equity and fixed income securities and the returns of a composite of indices of securities with characteristics similar to those the Portfolio typically holds. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202011.69%Worst Quarter1st quarter, 2020-10.77% Best Quarter 2020-06-30 0.1169 Worst Quarter 2020-03-31 -0.1077 Average Annual Total Return(for periods ended December 31, 2023) 0.1307 0.0673 0.0534 0.2629 0.1570 0.1203 0.0553 0.0110 0.0181 0.1398 0.0743 0.0592 INVESTMENT OBJECTIVE The investment objective of the Portfolio is to realize as high a level of total return as is consistent with reasonable investment risk. FEES AND EXPENSES OF THE PORTFOLIO The table below describes the fees and expenses that you may pay when you buy and hold interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher. Shareholder Fees(fees paid directly from your investment) Annual Portfolio Operating Expenses(expenses that you pay each year as a percentage of the value of your investment) 0.0053 0 0.0005 0.0043 0.0101 -0.0043 0.0058 Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. April 30, 2025 Example This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. The Example reflects adjustments made to the Portfolio's operating expenses due to the fee waiver agreement with the investment adviser for the first year only. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 59 279 516 1197 Portfolio Turnover The Portfolio 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. These costs, which are not reflected in Annual Portfolio Operating Expenses or in the Example, affect the Portfolio’s performance. During the most recent fiscal year, the Portfolio’s portfolio turnover rate was 10.57% of the average value of its portfolio. 0.1057 PRINCIPAL INVESTMENT STRATEGIES Investing in multiple investment asset classes, the Portfolio attempts to capitalize on the variation in return potential produced by the interaction of changing financial markets and economic conditions while maintaining a balance over time between investment opportunities and their associated potential risks by following a flexible policy of allocating assets.The Portfolio is tactically and strategically managed to capitalize on changing financial markets and economic conditions following a flexible policy for allocating assets utilizing the following strategic asset class target ranges:Equity and Other* ExposureFixed Income or Debt ExposureCash Equivalents60 – 80%20 – 40%0 – 10%*Other exposure includes REIT and commodity-related investments.These foregoing percentage target ranges are not intended to establish minimum and maximum limits. The adviser may deviate from the asset class target ranges in pursuit of total return and in response to changing market and economic conditions, and, may invest a greater or lesser percentage in any strategic asset class component when the adviser deems it favorable to do so in order to achieve the Portfolio’s investment objective.The Portfolio operates primarily as a “fund of funds” to gain the Portfolio’s multi-asset class exposure. The fund may invest in underlying Portfolios of Northwestern Mutual Series Fund, Inc. (each, an “Underlying Portfolio”) and exchange-traded funds (“ETFs”) which are not portfolios of Northwestern Mutual Series Fund, Inc. The Portfolio may obtain equity exposure by investing in one or more of the domestic or international Underlying Portfolios or ETFs and may obtain fixed income exposure by investing in one or more of the fixed income Underlying Portfolios or ETFs. The cash equivalent portion of the Portfolio may include, but is not limited to, ETFs, investments in debt securities issued or guaranteed by the U.S. government or its agencies or instrumentalities, including mortgage- and asset-backed securities, as well as commercial paper, banker’s acceptances, certificates of deposit and time deposits. In order to enhance short duration returns, the adviser may purchase ultra-short bond ETFs. For purposes of the strategic asset class ranges utilized herein, the adviser includes these instruments in the Cash Equivalents asset class together with cash and cash equivalent instruments. The Portfolio may also invest in ETFs that invest in real estate investment trusts (REITs). The Portfolio may invest in commodities through the purchase of swaps on physical commodities or commodity indices, including those which are traded in over-the-counter markets (“OTC”). The Portfolio may also invest in ETFs for purposes of obtaining exposure to commodities markets. The adviser allocates the Portfolio’s assets among the Underlying Portfolios and ETFs based on the adviser’s economic and market outlook and the investment objectives and strategies of the Underlying Portfolios and ETFs. With respect to the equity and international Underlying Portfolios and ETFs, the adviser considers their investment focus on small, mid or large market capitalizations, domestic or foreign investments, whether the Underlying Portfolio or ETF is diversified or non-diversified and whether it employs a “growth” or “value” style of investing, among other characteristics. With respect to fixed income Underlying Portfolios and ETFs, the adviser considers their focus on investment grade or non-investment grade securities, domestic or foreign investments, whether the issuer is a government or government agency, the duration (that is, a measure of the sensitivity to changes in interest rates) and maturity of the Underlying Portfolio or ETF, and other characteristics. The adviser regularly reviews and adjusts the allocation among the Underlying Portfolios and ETFs to favor investments in those Underlying Portfolios and ETFs that the adviser believes provide the most favorable position for achieving the Portfolio’s investment objective. In connection with the allocation process, the Portfolio may invest more than 25% of its assets in one Underlying Portfolio or one ETF.Through its investments in the equity Underlying Portfolios and ETFs, the Portfolio may be exposed to a wide range of equity securities and other instruments, including small, mid and large cap U.S. and non-U.S. stocks. Equity securities could include common and preferred stocks, securities convertible into stocks and depositary receipts for those securities. Through its investments in the fixed income Underlying Portfolios and ETFs, the Portfolio may be exposed to a wide range of fixed income securities with varying durations and maturities, including investment grade and non-investment grade debt securities, debt of corporate and government issuers, inflation-indexed debt securities, and other fixed income instruments. The Fund considers a fixed income security to be investment grade if the security is rated investment grade by at least two of the three credit rating agencies (BBB- or higher by S&P; Baa3 or higher by Moody’s; BBB- or higher by Fitch) and a security to be non-investment grade if the security is rated below investment grade by at least two of the three credit ratings agencies (BB+ or lower by S&P; Ba1 or lower by Moody’s; BB+ or lower by Fitch). An Underlying Portfolio or ETF may invest a large percentage of its assets in a single issuer, security, market or sector (or a limited group thereof) or in the case of an international Underlying Portfolio or ETF, may invest in emerging markets, a small number of countries or a particular geographic region. An Underlying Portfolio or ETF may also use certain derivative instruments including futures, forwards, options and swaps to meet its investment objective and for cash management purposes.When the adviser deems it to be more efficient or advantageous in managing the Portfolio, the adviser may utilize futures, options, forwards and swap agreements (including the purchase and sale of total return equity swaps and credit default swaps) to gain additional exposure to certain markets, sectors, regions, or commodities, as alternatives to investments in Underlying Portfolios or ETFs, to adjust the Portfolio for the adviser’s view on style or term structure and duration, to provide increased flexibility in asset allocation, to earn income and to otherwise seek to enhance returns or to hedge foreign currency exposure.The Portfolio is designed primarily for investors who want their investment allocated across major asset classes while pursuing the growth potential of equities with a smaller allocation to bonds. The investor should be willing to accept fluctuation in share prices that are typical for a portfolio that holds equity investments. PRINCIPAL RISKS Portfolio shares will rise and fall in value and there is a risk you could lose money by investing in the Portfolio. There can be no assurance that the Portfolio will achieve its objective. •Active Management Risk – The adviser’s investment strategies and techniques may not perform as expected which could cause the Portfolio to underperform other mutual funds or lose money. •Affiliated Portfolio Risk – In managing the Portfolio, the adviser has the authority to select, and allocate among, Underlying Portfolios. The adviser may be subject to potential conflicts of interest in selecting Underlying Portfolios because the fees paid to it by some Underlying Portfolios are higher than the fees paid by other Underlying Portfolios. Moreover, a situation could occur where proper action for the Portfolio could be adverse to the interest of the Underlying Portfolios or vice versa. •Asset Allocation Risk – This Portfolio allocates its investments among multiple investment asset classes and among Underlying Portfolios and ETFs, based upon judgments made by the adviser. The Portfolio could miss attractive investment opportunities by underweighting markets or sectors where there are significant returns, and could lose value by overweighting markets where there are significant declines, or may not correctly predict the times to shift assets from one type of investment to another. •Commodities Risk – The Portfolio’s investments in ETFs and total return swaps whose performance is linked to the price of an underlying commodity or commodity index may be subject to the risks of investing in physical commodities, including risks posed by regulatory, economic and political developments, weather events, natural disasters and market disruption. Commodity prices may have greater volatility than investments in traditional securities.•Derivatives Risk – The value of a derivative generally depends upon, or is derived from, an underlying asset, reference rate or index. The primary risks associated with the Portfolio’s use of derivatives are the risk that changes in the value of the derivatives may not correlate as intended with the underlying asset, rate or index, the risk of adverse price movements in the market, the risk of missed opportunities in other investments and the risk that the counterparty to a derivatives transaction fails to make the required payment or otherwise comply with the terms of the contract. Certain derivatives involve leverage, which could cause the Portfolio to lose more than the principal amount invested. Other risks include management, interest rate and liquidity risks. The Portfolio’s purchase of forwards and futures contracts may involve risks related to imperfect correlation between the prices of such instruments and the price of the underlying asset, as well as leverage, liquidity and volatility risks. In addition, the purchase of forwards also involves counterparty credit risk as well as heightened market risk. The Portfolio’s purchase of total return equity swap agreements and total return commodities swap agreements may pose risk arising from losses if the underlying reference asset does not perform as anticipated; such agreements are also subject to counterparty credit, liquidity and leveraging risks. The Portfolio’s use of options involve risk related to the direction and timing of market movements in the price of the underlying asset, obligations related to exercise of the option, and potential loss in value of the initial investment. •Convertible Securities Risk – Convertible securities (which can be bonds, notes, debentures, preferred stock, or other securities which are convertible into or exercisable for common stock), are subject to both the credit and interest rate risks associated with fixed income securities and to the stock market risk associated with equity securities. The value of a convertible security may not increase or decrease as rapidly as the underlying common stock. The Portfolio may be forced to convert a security before it would otherwise choose, which may have an adverse effect on the Portfolio’s ability to achieve its investment objective. •Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security held directly or through an Underlying Portfolio or ETF is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity. •Emerging Markets Risk – Investing in emerging market securities increases foreign investing risk, and may subject the Portfolio to more rapid and extreme changes in the value of its holdings compared with investments made in U.S. securities or in foreign, developed countries. Investments in emerging markets may be subject to political, economic, legal, market, and currency risks. Emerging market securities trade in smaller markets which may experience significant price and market volatility, fluctuations in currency values, interest rates and commodity prices, higher transaction costs, and the increased likelihood of the occurrence of trading difficulties, such as delays in executing, clearing and settling Portfolio transactions or in receiving payment of dividends. Special risks associated with investments in emerging market issuers may include a lack of publicly available information, a lack of uniform disclosure, accounting, financial reporting, and recordkeeping standards, and more limited investor protection provisions when compared with developed economies. Emerging market risks also may include unpredictable and changing political, economic and tax policies, the imposition of capital controls and/or foreign investment limitations by a country, nationalization of businesses, and the imposition of sanctions or restrictions in certain investments by other countries, such as the United States. Investments in Chinese securities may be more vulnerable to political and economic risks than investments in securities from other countries. The Chinese government could, at any time, alter or discontinue the economic reform programs implemented since 1978 which liberalized trade policy and reduced government control. Changes in these policies could adversely affect Chinese companies or investments in those companies and could substantially affect the value of China’s currency relative to the U.S. dollar. In addition, any public health threat or similar issue could have a significant impact on the Chinese economy, which in turn could adversely affect the Portfolio’s investments. •Equity Securities Risk – The value of equity securities held through the Underlying Portfolios and ETFs, such as common and preferred stocks, could decline if the financial condition of the companies an Underlying Portfolio or ETF is invested in declines or if overall market and economic conditions deteriorate. Equity securities generally have greater price volatility than fixed income securities. •Exchange Traded Funds Risk – Investing in exchange traded funds (ETFs) may expose the Portfolio to greater risk of loss and price fluctuation than investing directly in a comparable portfolio of stocks comprising the index due to lack of liquidity, the additional expenses incurred as a shareholder in another investment company, and tracking error. ETFs are also subject to the risk that their market prices may trade at a premium or discount to their net asset value, which means the Portfolio will overpay for an ETF’s assets if it is trading at a premium and will get less than the value of the ETF’s assets when selling if it is trading at a discount. An active market for an ETF may not be developed or maintained. Trading of an ETF’s shares may be halted by the exchange, in which case the Portfolio would be unable to sell its ETF shares unless and until trading is resumed. Investing in ultra-short bond ETFs may pose greater risk than investments in cash equivalents such as money market mutual funds, including risks associated with the credit quality, duration and interest rate sensitivity of the bond instruments held within such ETFs. Ultra-short bond ETFs may be more volatile and involve greater credit and interest rate risk than money market funds and other cash equivalents. In addition, the price of an ultra-short bond ETF may fluctuate, while the goal of a money market mutual fund is to maintain its NAV at a stable $1 per share. Ultra-short bond ETFs may lose money despite a stated investment objective of returning capital. •Foreign Investing Risk – Exposure to investments in foreign securities, including through Underlying Portfolios and ETFs, may subject the Portfolio to more rapid and extreme changes in value or more losses than a fund that invests exclusively in U.S. securities. This risk is due to potentially smaller markets, differing reporting, accounting and auditing standards, and nationalization, expropriation or confiscatory taxation, currency blockage, political and economic conditions, or diplomatic developments. Foreign securities may be adversely affected by decreases in foreign currency values relative to the U.S. dollar and may be less liquid, more volatile, and harder to value than U.S. securities. Exposure to investments in emerging markets heighten these risks due to a lack of established legal, political, business and social frameworks to support securities markets. •Fund of Funds Investing Risk – The Portfolio’s investment performance is significantly impacted by the investment performance of the Underlying Portfolios and ETFs it holds. The ability of the Portfolio to meet its investment objective is related to the ability of the Underlying Portfolios or ETFs to meet their respective investment objectives as well as the adviser’s allocation decisions with respect to the Underlying Portfolios and ETFs. Each of the Underlying Portfolios and ETFs has its own investment risks, and the Portfolio is indirectly exposed to all the risks of the Underlying Portfolios and ETFs in direct proportion to the amount of assets the Portfolio allocates to each Underlying Portfolio and each ETF. To the extent that the Portfolio invests a significant portion of its assets in a single Underlying Portfolio or ETF, it will be particularly sensitive to the risks associated with that Underlying Portfolio or ETF. Changes in the value of that Underlying Portfolio or ETF may have a significant effect on the Portfolio’s net asset value. The Portfolio will bear a pro rata share of the Underlying Portfolios’ or ETFs’ expenses. •Geographic Focus Risk – The Portfolio’s performance could be more volatile than that of a more geographically diversified fund and could be significantly impacted as a result of the Portfolio investing a relatively large percentage of its assets in issuers located in a single country, a small number of countries, or a particular geographic region. Also, the Portfolio’s performance may be more closely tied to the market, currency, economic, political, or regulatory conditions in those countries or that region. Similarly, the extent to which an Underlying Portfolio or ETF invests a significant portion of its assets in a single country, a small number of countries or a particular geographic region, may also adversely impact the Portfolio, depending on the Portfolio’s level of investment in that Underlying Portfolio or ETF. •High Yield Debt Risk – High yield debt securities (so called “junk bonds”) in which the Portfolio has exposure have greater interest rate and credit risk, may be more difficult to sell or sell at a reasonable price, have greater risk of loss than higher rated securities, and are predominantly speculative with respect to an issuer’s ability to pay interest and repay principal. In addition, high yield debt securities may be particularly sensitive to changes in the securities markets. •Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In a rising interest rate environment, the value of the Portfolio’s fixed income investments to which the Portfolio has exposure is likely to decline. A significant rise in interest rates over a short period of time could cause significant losses in the market value of the Portfolio’s fixed income instruments. Duration measures the price sensitivity of a fixed income instrument to changes in interest rates. The Portfolio’s exposure to fixed income instruments and Underlying Portfolios or ETFs with a longer average portfolio duration will be more sensitive to changes in interest rates than those with a shorter average duration. •Investment Style Risk – The Portfolio is subject to risks associated with an Underlying Portfolio’s or ETF's particular style of investing, such as growth or value or a combination of both, and may underperform with respect to its allocation to the Underlying Portfolio or ETF when the market does not favor that particular investment style. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. •Large Cap Company Risk – Exposure to investments in large cap stocks could cause the Portfolio to underperform in markets favoring faster growing companies. Large cap stocks tend to be more mature with fewer opportunities to grow and may not have the same growth potential as stocks with smaller capitalizations. •Large Transaction Risk – The Underlying Portfolios are used as investments for certain fund of funds, including the Portfolio, and may have a large percentage of their shares owned by such funds. Large redemption activity by the Portfolio or another fund of funds could result in the Underlying Portfolio being forced to sell portfolio securities at a loss to meet redemptions. The adviser may coordinate directly with the portfolio managers of the Underlying Portfolios to attempt to ensure that transactions are accommodated efficiently, including possibly implementing trades over a period of days rather than all at once. These practices may temporarily affect the adviser’s ability to fully implement the Portfolio’s investment strategies. •Liquidity Risk – Particular investments, such as small and micro cap stocks, fixed income securities, foreign securities, in particular emerging markets securities, and derivatives to which the Portfolio has exposure, can be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn. •Market Risk – The risk that the market price of securities owned by the Portfolio or an Underlying Portfolio or ETF in which the Portfolio invests may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments. •Micro Cap Company Risk – Exposure to investments in micro cap stocks may cause the Portfolio to experience more rapid and extreme changes in value than a fund that invests solely in small, mid and large cap stocks due to a more limited track record, narrower product markets, more limited resources, higher risk of failure, and less liquid trading markets. •Mortgage- and Asset-Backed Securities Risk – The risks of investing in mortgage-related and other asset-backed securities, including interest rate risk, credit risk, liquidity risk, extension risk and prepayment risk. Mortgage-related and other asset-backed securities represent interests in pools of mortgages or other assets and often involve risks that are different or possibly more acute than risks associated with other types of debt instruments. The value of some mortgage- or asset-backed securities may be particularly sensitive to changes in prevailing interest rates. •Preferred Stocks Risk – Preferred stocks often lack a fixed maturity or redemption date and are therefore more susceptible to price fluctuations when interest rates change. They also carry a greater risk of non-receipt of income because unlike interest on debt securities, dividends on preferred stocks must be declared by the issuer’s board of directors before becoming payable. •REITs Risk – Investments in REITs are subject to the types of risks associated with investing in the real estate industry, including, among other risks: adverse developments affecting the real estate industry; declines in real property values; changes in interest rates; defaults by mortgagors or other borrowers and tenants; lack of availability of mortgage funds or financing; extended vacancies of properties, especially during economic downturns; casualty or condemnation losses; property taxes and operating losses; and governmental actions, such as changes to tax laws, zoning regulations or environmental regulations. REITs are dependent upon the quality of their management, may have limited financial resources and heavy cash flow dependency, may not be diversified geographically or by property type, and may be subject to self-liquidation. •Sector Focus Risk – To the extent the Portfolio invests in Underlying Portfolios or ETFs with a relatively high percentage of its assets in a particular sector, it will have greater exposure to the risks associated with that sector, including the risk that the securities of companies within the sector will underperform due to adverse economic conditions, regulatory or legislative changes, or increased competition affecting the sector. To the extent the Portfolio invests in Underlying Portfolios or ETFs that are underweight in other sectors, the Portfolio risks missing out on advances in those sectors. •Small and Mid Cap Company Risk – Exposure to investments in small and mid cap stocks may cause greater risk of loss and price fluctuation than investing in stocks of larger cap companies due to a more limited track record, narrower product markets, more limited resources and less liquid trading markets. These stocks may be more volatile and more difficult to buy and sell than stocks with larger capitalizations. •U.S. Government Securities Risk – Not all obligations of the U.S. government, its agencies and instrumentalities are backed by the full faith and credit of the U.S. Treasury. Some obligations are backed only by the credit of the issuing agency or instrumentality, and in some cases there may be some risk of default by the issuer. Any guarantee by the U.S. government or its agencies or instrumentalities of a security held by the Portfolio does not apply to the market value of such security or to shares of the Portfolio itself. PERFORMANCE The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance for both equity and fixed income securities and the returns of a composite of indices of securities with characteristics similar to those the Portfolio typically holds.Returns are based on past results and are not an indication of future performance.Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table accompanying the bar chart shows the Portfolio’s average annual total return over certain time periods and compares the Portfolio’s returns with those of a broad measure of market performance for both equity and fixed income securities and the returns of a composite of indices of securities with characteristics similar to those the Portfolio typically holds. Returns are based on past results and are not an indication of future performance. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected. Quarter/YearReturnBest Quarter2nd quarter, 202014.30%Worst Quarter1st quarter, 2020-14.95% Best Quarter 2020-06-30 0.1430 Worst Quarter 2020-03-31 -0.1495 Average Annual Total Return(for periods ended December 31, 2023) 0.1524 0.0828 0.0626 0.2629 0.1570 0.1203 0.0553 0.0110 0.0181 0.1669 0.0925 0.0706 The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Effective May 1, 2024, the Portfolio modified the constituent components of the Balanced Portfolio Blended Composite Benchmark (the “Composite Benchmark”) and changed the target weightings across the Composite Benchmark components. As of such date, the Composite Benchmark was modified to (i) delete the high yield component and add real estate and commodities components; and (ii) replace Russell® Indices with S&P® Indices for each of the three domestic equity Composite Benchmark components. Performance of the Portfolio for periods prior to May 1, 2024, are relative to the updated Composite Benchmark. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written expense limitation agreement under which it has agreed to limit the total expenses of the Portfolio (excluding taxes, brokerage, other investment-related costs, interest and dividend expenses and charges, acquired fund fees and expenses and such non-recurring and extra ordinary expenses as they may arise) to an annual rate of 0.65% of the Portfolio's average net assets. This expense limitation agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Restated to reflect current expenses. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Restated to reflect current expenses. Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Includes fees and expenses incurred indirectly by the Portfolio as a result of investments in other investment companies (Acquired Fund Fees and Expenses). The operating expenses of the Portfolio reflected in the Portfolio's most recent annual report and Financial Highlights do not include the Acquired Fund Fees and Expenses. The Portfolio's investment adviser has entered into a written agreement to waive a portion of its management fee. This fee waiver agreement may be terminated by the adviser at any time after April 30, 2025. Effective May 1, 2024, the Portfolio modified the constituent components of the Asset Allocation Portfolio Blended Composite Benchmark (the “Composite Benchmark”) and changed the target weightings across the Composite Benchmark components. As of such date, the Composite Benchmark was modified to (i) delete the high yield component and add real estate and commodities components; and (ii) replace Russell® Indices with S&P® Indices for each of the three domestic equity Composite Benchmark components. Performance of the Portfolio for periods prior to May 1, 2024, are relative to the updated Composite Benchmark.