Loomis Sayles Funds Ii N-CSRCertified annual shareholder report (management investment company)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED

MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number: 811-06241

Loomis Sayles Funds II

(Exact name of Registrant as specified in charter)

888 Boylston Street, Suite 800

Boston, Massachusetts 02199-8197

(Address of principal executive offices) (Zip code)

Russell L. Kane, Esq.

Natixis Distribution, L.P.

888 Boylston Street, Suite 800

Boston, Massachusetts 02199-8197

(Name and address of agent for service)

Registrant’s telephone number, including area code: (617) 449-2822

Date of fiscal year end: December 31

Date of reporting period: December 31, 2020

Item 1. Reports to Stockholders.

The Registrant’s annual report transmitted to shareholders pursuant to Rule 30e-1 under the Investment Company Act of 1940 is as follows:

Annual Report

December 31, 2020

Loomis Sayles High Income Fund

Loomis Sayles Intermediate Municipal Bond Fund

Loomis Sayles International Growth Fund

Loomis Sayles Investment Grade Bond Fund

Loomis Sayles Strategic Alpha Fund

Loomis Sayles Strategic Income Fund

Table of Contents

LOOMIS SAYLES HIGH INCOME FUND

Investment Goal

The Fund seeks high current income plus the opportunity for capital appreciation to produce a high total return.

Market Conditions

The financial markets experienced significant volatility in 2020, as investors grappled with the persistent uncertainty surrounding Covid-19. The bulk of the market disruptions occurred in February and March, when world governments first aimed to contain the virus by locking down broad swaths of their economies. Higher-risk assets were hit hard in the ensuing selloff, while demand for “safe-haven” investments surged. The US Federal Reserve (Fed) sought to counter the extraordinary developments by cutting short-term interest rates to zero, reestablishing traditional quantitative easing (QE) through asset purchases in the Treasury and mortgage-backed securities markets, and establishing lending facilities which either have only been used during the Great Financial Crisis or were created for the first time in Fed history, such as the Corporate Credit facility. Aided by the $2.2 trillion stimulus package passed by the US Congress in late March, the Fed’s response fueled an impressive recovery in higher-risk assets from early spring onward. After pausing in the lead-up to the US elections, the rally gained steam in November thanks to the long-awaited headline that coronavirus vaccines would soon become available to the public. The markets took this as an indication that economic conditions could gradually return to normal in 2021, boosting sentiment into year-end.

US Treasurys were the primary beneficiaries of the first-quarter “flight to quality” and the Fed’s subsequent commitment to maintain its low-rate monetary policy indefinitely. Twelve-month returns were progressively higher along the yield curve (a curve that shows the relationship among bond yields across the maturity spectrum), with 30-year issues generating the largest gain.

Although investment-grade corporate bonds suffered a sharp downturn in the February-March selloff, the category finished as the top performing major segment of the fixed income market for the full, 12-month period. Corporates benefited from the gradual improvement in the credit outlook throughout the course of the year, together with rising demand for high-quality alternatives to low-yielding government debt.

High-yield bonds also delivered positive returns, although they were unable to keep pace with investment-grade corporates. The category was supported by hopes for an economic recovery and reduced investor risk aversion. Lower-quality debt was generally harder hit in the February-March downturn due low market liquidity, tempering its return for the full year. Nevertheless, yield spreads — the difference between yields on below investment-grade debt and Treasurys of similar maturities — finished the year close to where they stood in February prior to the selloff associated with Covid-19.

Securitized assets — including mortgage-backed securities (MBS), asset-backed securities (ABS), and commercial mortgage-backed securities (CMBS) — posted positive total returns but failed to keep pace with the broader US bond market. CMBS was the strongest performer in this segment despite concerns about the outlook for commercial real estate in the wake of the pandemic.

Performance Results

For the 12 months ended December 31, 2020, Class Y shares of the Loomis Sayles High Income Fund returned 8.19% at net asset value. The Fund outperformed its benchmark, the Bloomberg Barclays U.S. Corporate High-Yield Bond Index, which returned 7.11%.

Explanation of Fund Performance

The remarkable events of 2020 were dominated by the volatility created by the Covid-19 global pandemic. Fueled by extraordinary monetary and fiscal stimulus, markets came roaring back after a sharp selloff during the first quarter of the year, and continued to reach new highs as lockdowns eased and vaccine development progressed. This positive momentum was maintained throughout the final quarter of 2020 as a Covid vaccine was approved and distribution began. Security selection was the primary source of the Fund’s outperformance for the 12-month period. High yield and investment grade corporate credit positions were the largest positive contributors to relative return, aided by consumer cyclical and energy holdings. Exposures to the communications sector within high yield and capital goods sector within investment grade credit were also beneficial for performance.

An allocation to securitized assets detracted as this sector did not keep pace with high yield credit. Within convertible securities, selected energy and consumer non-cyclical holdings weighed on return.

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Outlook

Looking ahead to the upcoming year, there are a number of structural economic factors in place that pose risks to our market outlook, including the ongoing impact of the pandemic, further delay in reaching a fiscal package and any resurgence of trade tensions between the US and China. That said, we are optimistic that economic conditions could continue to show improvement over the next year. This view is reflected in current market prices and appears to be shared by the consensus.

While the recent rise in coronavirus cases has led to renewed containment measures across the US, the likelihood of a vaccine has been priced into markets along with expectations for a fiscal package to arrive in the first quarter of the year. These measures help give us some confidence that the economic recovery could continue to show steady, if uneven, progress. GDP growth rebounded from the steep declines last year and we expect this trend to continue into 2021.

We anticipate limited changes in monetary policy, with the Fed likely maintaining its zero interest rate policy until at least 2023. The Fed has also indicated that full employment and longer-term inflation averages are additional factors in considering any future rate hikes. This accommodative stance should continue to boost investor confidence and demand for yield in a low global rate environment. In addition, we believe the overall health of the consumer, strong housing market and expected inventory rebuilding provide support to our outlook.

The credit markets have been progressing through the cycle,¹ and we believe there are increasing signs of a shift towards recovery with corporate profits rebounding, easy monetary policy, balance sheet improvement and potential for large-scale vaccine distribution.

We have been maintaining a balance of liquidity, diversification and risk exposure in our portfolios. Within our credit allocation, we continue to focus on areas where we still see value based on our fundamental research. We are specifically focused on some of the sectors that were hardest hit by the pandemic including the transportation, recreational and hospitality industries. These areas of the economy include credits that have been cheap for their rating, have been able to access the capital markets for liquidity and are likely in a good position to benefit from the recovery.

Despite the higher valuations, we believe there are still selective opportunities in both the investment grade and high yield corporate sectors. Spreads have compressed but can potentially tighten further on improving fundamentals. We are selectively adding corporate credit, particularly in areas of the market that have lagged the recovery.

Our emerging market allocation largely represents US dollar-pay exposure to high quality securities with strong balance sheets and currently attractive real yields. We are holding little foreign currency but continue to evaluate opportunities in markets outside the US as we look for clarity on the outlook for global growth.

Market conditions in the past year have highlighted the notion that investors tend to overreact. The speed and severity of the recession and subsequent sharp rebound were unexpected, but also presented some favorable investment opportunities. These developments have served to reinforce our investment philosophy that markets are highly inefficient in the short term. We believe that we were able to capitalize on these developments in 2020 and that our portfolios are well-positioned to benefit from the expected economic growth and recovery in the new year.

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LOOMIS SAYLES HIGH INCOME FUND

Hypothetical Growth of $100,000 Investment in Class Y Shares³

December 31, 2010 through December 31, 2020

Average Annual Total Returns — December 31, 2020³

Performance data shown represents past performance and is no guarantee of, and not necessarily indicative of, future results. Total return and value will vary, and you may have a gain or loss when shares are sold. Current performance may be lower or higher than quoted. For most recent month-end performance, visit im.natixis.com/performance. Performance for other share classes will be greater or less than shown based on differences in fees and sales charges. You may not invest directly in an index. Performance for periods less than one year is cumulative, not annualized. Returns reflect changes in share price and reinvestment of dividends and capital gains, if any. The table(s) do not reflect taxes shareholders might owe on any fund distributions or when they redeem their shares.

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LOOMIS SAYLES INTERMEDIATE MUNICIPAL BOND FUND

Investment Goal

The Fund seeks a high level of federal tax-exempt current income, consistent with the preservation of capital.

Market Conditions

Capital markets concluded a tumultuous year producing positive returns across most asset classes. High-grade municipal yields declined between 70 and 90 basis points, with the largest declines occurring on the shorter end of the yield curve. The pandemic-induced market panic that occurred in March proved short-lived as a rapid and massive easing of monetary policy, combined with multiple rounds of fiscal relief, provided the medicine markets required to gain a foothold from the liquidity panic. Markets subsequently began their climb higher as the year progressed. Lower quality sectors of the municipal market underperformed higher quality, as participants weighed the continued impact of a deep recession caused by the necessity of shutting down large segments of the US and global economies. Recent economic improvement coincident with the approval and rollout of vaccines has increased optimism that the recession will end in 2021 and the path toward recovery will open. However, significant hurdles remain for large segments of the economy, and whether the severity of the pandemic will result in long-term or permanent changes in behavior continues to weigh on many sectors, including real estate related, mass transit, senior care and air travel, to note several. In addition, the disruption and dislocation in K-12 and higher education has been sharp, although federal aid has provided important support. Questions remain, however, about the evolution of the education sector and whether the steady expansion of higher education, in particular, has reached a secular peak in the US.

Performance Results

For the 12 months ended December 31, 2020, Class Y shares of the Loomis Sayles Intermediate Municipal Bond Fund returned 3.63% at net asset value. The Fund underperformed its benchmark, the Bloomberg Barclays Municipal Bond Index, which returned 5.21%.

Explanation of Fund Performance

Although the Fund produced a meaningfully positive return for the year, it underperformed its benchmark primarily due to yield curve posture, more specifically a 10.5% underweight to the longest portion of the yield curve (22 years and plus), which produced the greatest returns for the period. Additionally, overweight exposures to the higher education and hospital sectors hampered performance as spreads widened, while outperformance of the Fund’s allocations to the local general obligation, leasing and special tax sectors was additive to performance. Furthermore, underperformance in the Fund’s BBB-rated credits was a significant detractor from performance. With respect to state allocations, fund positioning in two of the largest states in the benchmark, California and New York, contributed positively; however, overall state exposure was a drag on performance.

Outlook

The economy and the markets withstood significant damage in the early stages of the pandemic and required unprecedented support from fiscal and monetary policymakers. The Federal Reserve has communicated clearly its intention to continue to keep the policy rate near the zero lower bound at least through this year and likely beyond. Sustaining an economic recovery is also expected to require continuing fiscal relief while the rollout of the vaccines continues and accelerates. We anticipate the new administration will attempt to bring both additional aid for state and local governments and an infrastructure package. We are hopeful that wide distribution of the vaccine alongside continued fiscal and monetary support will provide a glide path toward economic recovery. While we do not anticipate a significant rise in long-term interest rates, there could be modest upward pressure as the economic environment improves. Somewhat higher yields and an increase in municipal supply resulting from an infrastructure package would be welcome developments for municipal investors who have faced constrained supply and record low yields for most of the past year. Municipal investor appetite remains strong and we anticipate the market could absorb any increase in supply.

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LOOMIS SAYLES INTERMEDIATE MUNICIPAL BOND FUND

Hypothetical Growth of $100,000 Investment in Class Y Shares^1,4

December 31, 2012 (inception) through December 31, 2020

Average Annual Total Returns — December 31, 2020⁴

Performance data shown represents past performance and is no guarantee of, and not necessarily indicative of, future results. Total return and value will vary, and you may have a gain or loss when shares are sold. Current performance may be lower or higher than quoted. For most recent month-end performance, visit im.natixis.com/performance. Performance for other share classes will be greater or less than shown based on differences in fees and sales charges. You may not invest directly in an index. Performance for periods less than one year is cumulative, not annualized. Returns reflect changes in share price and reinvestment of dividends and capital gains, if any. The table(s) do not reflect taxes shareholders might owe on any fund distributions or when they redeem their shares.

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LOOMIS SAYLES INTERNATIONAL GROWTH FUND

Investment Goal

The Fund’s investment goal is long-term growth of capital.

Market Conditions

International equities moved modestly higher in the abbreviated reporting period that ran from December 15, 2020 to December 31, 2020. The market entered the period on a high note, having rallied significantly over the prior six weeks following the approval of a vaccine for Covid-19. The conclusion of the U.S. election provided a further boost to the markets in this time, as did the ongoing commitment of the world’s central banks to maintain their ultra-accommodative monetary policies indefinitely. The pace of the rally slowed in the final two weeks of the year, as investors paused to digest the previous gains and trading activity decelerated around the holidays. In addition, a number of European countries began to re-institute lockdown measures to combat rising cases of the coronavirus. The tone in the markets remained fairly positive, however, partially as a result of the passage of a long-awaited fiscal stimulus package in the United States. The upbeat close to the year allowed the major international indices to finish 2020 with double-digit Q4 returns despite the dramatic first-quarter selloff caused by Covid-19.

Performance Results

The Loomis Sayles International Growth Fund was launched on December 15, 2020. For the period ending December 31, 2020, Class Y shares of the Fund returned 1.38% at net asset value. The Fund underperformed its benchmark, the MSCI All Country World Index Ex USA Index, which returned 2.57%.

Explanation of Fund Performance

We are an active manager with a long-term, private equity approach to investing. Through our proprietary bottom-up research framework, we look to invest in those few high-quality businesses with sustainable competitive advantages and profitable growth when they trade at a significant discount to intrinsic value. Given the rare confluence of quality, growth, and valuation, we may study dozens of companies but may only invest in a select few businesses each year. We believe identifying those few businesses with these characteristics is an art, not a science. As a result of this rigorous approach, ours is a selective, high-conviction portfolio of typically 30-45 securities.

During the brief period, the Fund’s positions in Baidu, Vipshop, and Kweichow Moutai contributed the most to performance. Stock selection in the communication services and consumer staples sectors, as well as our allocation in the energy sector, contributed positively to relative performance. The Fund’s positions in Alibaba, Tencent, and Sodexo detracted the most from performance. Stock selection in the consumer discretionary and information technology sectors were the biggest detractors from relative performance.

Outlook

Our investment process is characterized by bottom-up fundamental research and a long-term investment time horizon. The nature of the process leads to a lower-turnover portfolio in which sector positioning is the result of stock selection. The Fund ended the year with overweight positions in the consumer staples, consumer discretionary, healthcare, communication services, and information technology sectors and was underweight in the industrials and energy sectors. We had no exposure to stocks in the financials, materials, utilities or real estate sectors. From a geographic standpoint we were overweight in emerging markets and North America and underweight in developed Asia and Europe. We remain committed to our long-term investment approach to invest in those few high-quality businesses with sustainable competitive advantages and profitable growth when they trade at a significant discount to intrinsic value.

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LOOMIS SAYLES INTERNATIONAL GROWTH FUND

Top Ten Holdings as of December 31, 2020

The portfolio is actively managed and holdings are subject to change. There is no guarantee the Fund continues to invest in the securities referenced. The holdings listed exclude any temporary cash investments.

Total Returns — December 31, 2020³

Performance data shown represents past performance and is no guarantee of, and not necessarily indicative of, future results. Total return and value will vary, and you may have a gain or loss when shares are sold. Current performance may be lower or higher than quoted. For most recent month-end performance, visit im.natixis.com. Performance for other share classes will be greater or less than shown based on differences in fees and sales charges. You may not invest directly in an index. Performance for periods less than one year is cumulative, not annualized. Returns reflect changes in share price and reinvestment of dividends and capital gains, if any. The table(s) do not reflect taxes shareholders might owe on any fund distributions or when they redeem their shares.

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LOOMIS SAYLES INVESTMENT GRADE BOND FUND

Investment Goal

The Fund seeks high total investment return through a combination of current income and capital appreciation.

Market Conditions

The financial markets experienced significant volatility in 2020, as investors grappled with the persistent uncertainty surrounding Covid-19. The bulk of the market disruptions occurred in February and March, when world governments first aimed to contain the virus by locking down broad swaths of their economies. Higher-risk assets were hit hard in the ensuing selloff, while demand for “safe-haven” investments surged. The US Federal Reserve (Fed) sought to counter the extraordinary developments by cutting short-term interest rates to zero, reestablishing traditional quantitative easing (QE) through asset purchases in the Treasury and mortgage-backed securities markets, and establishing lending facilities which either have only been used during the Great Financial Crisisor were created for the first time in Fed history, such as the Corporate Credit facility. Aided by the $2.2 trillion stimulus package passed by the US Congress in late March, the Fed’s response fueled an impressive recovery in higher-risk assets from early spring onward. After pausing in the lead-up to the US elections, the rally gained steam in November thanks to the long-awaited headline that coronavirus vaccines would soon become available to the public. The markets took this as an indication that economic conditions could gradually return to normal in 2021, boosting sentiment into year-end.

US Treasurys were the primary beneficiaries of the first-quarter “flight to quality” and the Fed’s subsequent commitment to maintain its low-rate monetary policy indefinitely. Twelve-month returns were progressively higher along the yield curve (a curve that shows the relationship among bond yields across the maturity spectrum), with 30-year issues generating the largest gain.

Although investment-grade corporate bonds suffered a sharp downturn in the February-March selloff, the category finished as the top performing major segment of the fixed income market for the full, 12-month period. Corporates benefited from the gradual improvement in the credit outlook throughout the course of the year, together with rising demand for high-quality alternatives to low-yielding government debt.

High-yield bonds also delivered positive returns, although they were unable to keep pace with investment-grade corporates. The category was supported by hopes for an economic recovery and reduced investor risk aversion. Lower-quality debt was generally harder hit in the February-March downturn due low market liquidity, tempering its return for the full year. Nevertheless, yield spreads — the difference between yields on below investment-grade debt and Treasurys of similar maturities — finished the year close to where they stood in February prior to the selloff associated with Covid-19.

Securitized assets — including mortgage-backed securities (MBS), asset-backed securities (ABS), and commercial mortgage-backed securities (CMBS) — posted positive total returns but failed to keep pace with the broader US bond market. CMBS was the strongest performer in this segment despite concerns about the outlook for commercial real estate in the wake of the pandemic.

Performance Results

For the 12 months ended December 31, 2020, Class Y shares of the Loomis Sayles Investment Grade Bond Fund returned 11.68% at net asset value. The Fund outperformed its benchmark, the Bloomberg Barclays U.S. Government/Credit Bond Index, which returned 8.93%. The Fund also outperformed its secondary benchmark, the Bloomberg Barclays U.S. Aggregate Bond Index, which returned 7.51%.

Explanation of Fund Performance

The remarkable events of 2020 were dominated by the volatility created by the Covid-19 global pandemic. Fueled by extraordinary monetary and fiscal stimulus, markets came roaring back after a sharp selloff during the first quarter of the year, and continued to reach new highs as lockdowns eased and vaccine development progressed. This positive momentum was maintained throughout the final quarter of 2020 as a Covid vaccine was approved and distribution began. Security selection was the primary source of the Fund’s outperformance for the 12-month period. The Fund’s exposure to investment grade corporate credit was the largest contributor to relative return, aided by banking, communications and consumer non-cyclical holdings. An allocation to high yield corporate credit, particularly within the basic industry and energy sectors, was positive for performance as well. An underweight to US Treasuries was also beneficial as investors favored riskier asset classes given the improving economic outlook.

Exposure to securitized assets and defensive, reserve-like positions detracted as these did not keep pace with corporate credit.

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LOOMIS SAYLES INVESTMENT GRADE BOND FUND

Outlook

Looking ahead to the upcoming year, there are a number of structural economic factors in place that pose risks to our market outlook, including the ongoing impact of the pandemic, further delay in reaching a fiscal package and any resurgence of trade tensions between the US and China. That said, we are optimistic that economic conditions could continue to show improvement over the next year. This view is reflected in current market prices and appears to be shared by the consensus.

While the recent rise in coronavirus cases has led to renewed containment measures across the US, the likelihood of a vaccine has been priced into markets along with expectations for a fiscal package to arrive in the first quarter of the year. These measures help give us some confidence that the economic recovery could continue to show steady, if uneven, progress. GDP growth rebounded from the steep declines last year and we expect this trend to continue into 2021.

We anticipate limited changes in monetary policy, with the Fed likely maintaining its zero interest rate policy until at least 2023. The Fed has also indicated that full employment and longer-term inflation averages are additional factors in considering any future rate hikes. This accommodative stance should continue to boost investor confidence and demand for yield in a low global rate environment. In addition, we believe the overall health of the consumer, strong housing market and expected inventory rebuilding provide support to our outlook.

The credit markets have been progressing through the cycle,¹ and we believe there are increasing signs of a shift towards recovery with corporate profits rebounding, easy monetary policy, balance sheet improvement and potential for large-scale vaccine distribution.

We have been maintaining a balance of liquidity, diversification and risk exposure in our portfolios. Within our credit allocation, we continue to focus on areas where we still see value based on our fundamental research. We are specifically focused on some of the sectors that were hardest hit by the pandemic including the transportation, recreational and hospitality industries. These areas of the economy include credits that have been cheap for their rating, have been able to access the capital markets for liquidity and are likely in a good position to benefit from the recovery.

Despite the higher valuations, we believe there are still selective opportunities in both the investment grade and high yield corporate sectors. Spreads have compressed but can potentially tighten further on improving fundamentals. We are selectively adding corporate credit, particularly in areas of the market that have lagged the recovery.

Our emerging market allocation largely represents US dollar-pay exposure to high quality securities with strong balance sheets and currently attractive real yields. We are holding little foreign currency but continue to evaluate opportunities in markets outside the US as we look for clarity on the outlook for global growth.

Market conditions in the past year have highlighted the notion that investors tend to overreact. The speed and severity of the recession and subsequent sharp rebound were unexpected, but also presented some favorable investment opportunities. These developments have served to reinforce our investment philosophy that markets are highly inefficient in the short term. We believe that we were able to capitalize on these developments in 2020 and that our portfolios are well-positioned to benefit from the expected economic growth and recovery in the new year.

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LOOMIS SAYLES INVESTMENT GRADE BOND FUND

Hypothetical Growth of $100,000 Investment in Class Y Shares⁴

December 31, 2010 through December 31, 2020

Average Annual Total Returns — December 31, 2020⁴

Performance data shown represents past performance and is no guarantee of, and not necessarily indicative of, future results. Total return and value will vary, and you may have a gain or loss when shares are sold. Current performance may be lower or higher than quoted. For most recent month-end performance, visit im.natixis.com. Performance for other share classes will be greater or less than shown based on differences in fees and sales charges. You may not invest directly in an index. Performance for periods less than one year is cumulative, not annualized. Returns reflect changes in share price and reinvestment of dividends and capital gains, if any. The table(s) do not reflect taxes shareholders might owe on any fund distributions or when they redeem their shares.

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LOOMIS SAYLES STRATEGIC ALPHA FUND

Investment Goal

The Fund seeks to provide an attractive absolute total return, complemented by prudent investment management designed to manage risks and protect investor capital. The secondary goal of the Fund is to achieve these returns with relatively low volatility.

Market Conditions

Although investment-grade corporate bonds suffered a sharp downturn in the February-March 2020 selloff, the category finished as the top performing major segment of the fixed income market for the full 12-month period. Corporates benefited from the gradual improvement in the credit outlook throughout the course of the year, together with rising demand for high-quality alternatives to low-yielding government debt.

High-yield bonds also delivered positive returns, although they were unable to keep pace with investment-grade corporates. The category was supported by hopes for an economic recovery and reduced investor risk aversion. Lower-quality debt was generally harder hit in the February-March downturn due to low market liquidity, tempering its return for the full year. Nevertheless, yield spreads (the yield differential provided by corporate issues relative to comparable maturity Treasuries) finished the year close to where they stood in February prior to the selloff associated with Covid-19.

Emerging market bonds, while performing poorly in the first quarter, rebounded to finish the year with a solid total return. The asset class was aided by the combination of gradually improving investor sentiment, robust growth in Asia, steadily improving commodity prices, and persistent weakness in the US dollar.

Performance Results

For the 12 months ended December 31, 2020, Class Y shares of the Loomis Sayles Strategic Alpha Fund returned 10.19% at net asset value. The Fund outperformed its benchmark, 3-Month LIBOR, which returned 0.66% for the period. The Fund follows an absolute return strategy and is not managed to an index.

Explanation of Fund Performance

Investment grade corporate credit made the largest positive contribution during the period as spreads narrowed. To support the flow of credit to households and businesses, the Federal Reserve (Fed) will likely continue to purchase Treasury securities. With the coronavirus continuing to spread and disrupt markets, the Fed has taken many additional measures to keep the economy afloat such as buying investment grade corporate bonds with the intent of providing a safety net to corporations and their employees. However, one of President Joe Biden’s campaign promises was to reverse the excesses of the Trump tax cuts for corporations, so whether this impacts the current assistance measures the Fed is providing remains to be seen. Within the portfolio, consumer, banking and communications names in particular were the strongest contributors to returns.

High yield corporate bonds bolstered return during the period. Consumer, communications and finance company names led contributions within the high yield allocation as spreads narrowed. A portion of our high yield exposure was expressed through being long the market with High Yield CDX (credit default swap index), where we took advantage of the relatively strong liquidity profile that this instrument provided during the sharp market correction that occurred in the first quarter of 2020. The position performed well during the rest of the year and contributed positively to the overall performance of the Fund. The use of credit default swap/CDX instruments provided individual name and broad index exposure, and as a result, the ability to access overall credit markets and express an investment view quickly and efficiently. High yield bonds have outperformed stocks during the past few economic recoveries, but that has not happened this time around. As noted, against the backdrop of the coronavirus pandemic the Fed intervened with interest rate cuts, to which high yield bonds responded favorably. During the final quarter of 2020, multiple pharmaceutical and biotech companies confirmed they would soon make a Covid-19 vaccine available (while awaiting FDA approval) and verified effectiveness rates in the 95% range. As

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administration of the initial vaccines to healthcare workers and high risk individuals began, the resulting optimism fueled gains in the high yield bond market during the final quarter of 2020.

Emerging markets contributed to returns for the year with owned-no-guarantee oil securities in Mexico aiding performance the most. Since his inauguration in late 2018, Mexican President Andrés Manuel López Obrador has pledged to restore the dominance of local companies such as Pemex by reviving competition among energy companies and ending reforms that were implemented in 2013. Additionally, with the economy struggling due to the global pandemic, Mexico’s energy companies have worked hard to recover and build a solid future.

Currency positioning weighed on performance during the year as the dollar began 2020 as the world’s strongest currency only to see the coronavirus pandemic rock markets. A long forward position in the Norwegian krone particularly detracted. With the Fed’s extreme policy accommodation since late March the dollar has weakened against most major currencies. The US dollar is expected to continue to weaken in 2021 as Fed policies including historically low interest rates remain intact, the economy continues to repair and President Biden begins his first 100 days in office with less reliance on tariffs against China than his predecessor. The interest rate positioning was done using US Treasury futures, with gross notional exposure averaging approximately 10% of overall market value, to establish a duration underweight, which helped contribute positively to the overall performance of the Fund.

Our minimal allocation to bank loans hurt performance in 2020 with the energy sub-sector as the largest detractor. It should be noted that energy lending includes a wide range of financing activities with examples including oil and gas reserves, solar financing, solar farm financing, wind capital, wind farm financing, renewable and sustainable energy financing and biomass fuels financing. Furthermore, the Fed established the Primary Market Corporate Credit Facility for new bond and loan issuance to assist with the flow of credit to large employers impacted by the pandemic.

Outlook

Looking ahead to the upcoming year, there are a number of structural economic factors in place that pose risks to our market outlook, including the ongoing impact of the pandemic, potential delays in reaching agreement on further fiscal stimulus and any resurgence of trade tensions between the US and China. That said, we are optimistic that economic conditions could continue to show improvement over the next year. This view is reflected in current market prices and appears to be shared by the consensus.

We anticipate limited changes in monetary policy, with the Fed likely maintaining its zero interest rate stance until at least 2023. The Fed has also indicated that progress toward attaining full employment and longer-term inflation averages are additional factors in considering any future rate hikes. This accommodative stance should continue to boost investor confidence and demand for yield in a low global rate environment. In addition, we believe the overall health of the consumer, strong housing market and expected inventory rebuilding provide support to our outlook.

We have been maintaining a balance of liquidity, diversification and risk exposure. Within our credit allocation, we continue to focus on areas where we still see value based on our fundamental research. We are specifically focused on some of the sectors that were hardest hit by the pandemic including the transportation, recreation and hospitality industries. These areas of the economy include credits that we view as cheap for their rating, have been able to access the capital markets for liquidity and are likely in a good position to benefit from the recovery.

Despite their higher valuations, we believe there are still selective opportunities in both the investment grade and high yield corporate sectors. Spreads have compressed but can potentially tighten further on improving fundamentals. We are selectively adding corporate credit, particularly in areas of the market that have lagged the recovery.

Market conditions in the past year have highlighted the notion that investors tend to overreact. The speed and severity of the recession and subsequent sharp rebound were unexpected, but also presented some favorable investment opportunities. These developments have served to reinforce our belief that markets are highly inefficient in the short term. We believe that we were able to capitalize on these developments in 2020 and that the Fund is well-positioned to benefit from the expected economic growth and recovery in the new year.

Our emerging market allocation largely represents US dollar-pay exposure to high quality securities with strong balance sheets and currently attractive real yields. We are holding little foreign currency but continue to evaluate opportunities in markets outside the US as we look for clarity on the outlook for global growth.

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LOOMIS SAYLES STRATEGIC ALPHA FUND

Hypothetical Growth of $100,000 Investment in Class Y Shares⁴

December 31, 2010 through December 31, 2020

Average Annual Total Returns — December 31, 2020⁴

Performance data shown represents past performance and is no guarantee of, and not necessarily indicative of, future results. Total return and value will vary, and you may have a gain or loss when shares are sold. Current performance may be lower or higher than quoted. For most recent month-end performance, visit im.natixis.com/performance. Performance for other share classes will be greater or less than shown based on differences in fees and sales charges. You may not invest directly in an index. Performance for periods less than one year is cumulative, not annualized. Returns reflect changes in share price and reinvestment of dividends and capital gains, if any. The table(s) do not reflect taxes shareholders might owe on any fund distributions or when they redeem their shares.

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LOOMIS SAYLES STRATEGIC INCOME FUND

Investment Goal

The Fund seeks high current income with a secondary objective of capital growth.

Market Conditions

Investors’ appetite for risk surged in the fourth quarter, which contributed to a broad range of nearly all positive returns across credit asset classes. In early November, investors were treated to the long-awaited news that coronavirus vaccines were effective and would soon become available to the public. The prospect of a gradual return to normal economic conditions in 2021 allowed market participants to look beyond recent adverse headlines, including the emergence of a new strain of the virus, ongoing Brexit negotiations, and a slowdown in the economic recovery. Investors instead were focused on and encouraged by the US Federal Reserve (Fed) statements indicating its intention to keep short-term interest rates near zero for a multiyear period. Not least, the resolution to the US election removed a factor that had weighed on sentiment in early autumn.

The developments mentioned above acted as a headwind for the Treasury market. While short-term yields were largely unchanged due to the steady outlook for Fed policy, longer-term yields rose (as prices fell). With Treasurys already having rallied significantly in the first nine months of the year, there was little room for further improvement — particularly in light of rising estimates for both economic growth and inflation in 2021. In addition, demand for “safe haven” assets was muted due to generally positive headlines.

Investment-grade corporate bonds delivered sizable outperformance in the quarter, closing out an impressive year. The combination of an improving credit outlook and stable Fed policy prompted investors to move further out on the risk spectrum in search of more attractive yields.

High yield corporate issues performed very well and finished as the best performing major segment of the bond market for the quarter. Yield spreads — the difference between yields on below investment-grade debt and Treasurys of similar maturities — declined to a level close to where they stood in February prior to the selloff associated with Covid-19.

Securitized assets — including mortgage-backed securities (MBS), asset-backed securities (ABS) and commercial mortgage-backed securities (CMBS) — outperformed Treasurys but trailed both corporates and high yield. The category benefited from the same search for yield that aided other credit-sensitive segments of the fixed-income market, with CMBS outpacing ABS and MBS, respectively.

Emerging market bonds also moved higher in the quarter, with the bulk of the gain occurring in November and December. The asset class made up all of the ground it lost in the February-March selloff, allowing it to finish the full year firmly in positive territory. Emerging-markets debt was boosted by the combination of the “risk-on” environment, rising commodity prices and the persistent weakness in the US dollar.

Performance Results¹

For the three months ended December 31, 2020, Class Y shares of the Loomis Sayles Strategic Income Fund returned 5.44% at net asset value. The Fund outperformed its primary benchmark, the Bloomberg Barclays U.S. Aggregate Bond Index, which returned 0.67%.

Explanation of Fund Performance

Markets finished the year on a positive note as a Covid-19 vaccine was approved and distribution began on a global scale. Credit sectors continued to perform well under these conditions. The Fund’s exposure to high yield corporate credit was the biggest

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LOOMIS SAYLES STRATEGIC INCOME FUND

contributor to relative return, largely driven by consumer cyclical, energy, and finance company holdings. Exposure to non-US-dollar securities, particularly those denominated in the Mexican peso, helped performance during the period. Within equities, allocations to the communications, consumer non-cyclical and technology sectors generated positive relative performance as stock markets posted strong gains for the quarter.

The Fund’s longer-than-benchmark positioning with respect to duration (and corresponding interest rate sensitivity) within US Treasuries detracted from relative performance.

Outlook

Looking ahead to the upcoming year, there are a number of structural economic factors in place that pose risks to our market outlook, including the ongoing impact of the pandemic, further delay in reaching a fiscal package and any resurgence of trade tensions between the US and China. That said, we are optimistic that economic conditions could continue to show improvement over the next year. This view is reflected in current market prices and appears to be shared by the consensus.

While the recent rise in coronavirus cases has led to renewed containment measures across the US, the likelihood of a vaccine has been priced into markets along with expectations for a fiscal package to arrive in the first quarter of the year. These measures help give us some confidence that the economic recovery could continue to show steady, if uneven, progress. GDP growth rebounded from the steep declines last year and we expect this trend to continue into 2021.

We anticipate limited changes in monetary policy, with the Fed likely maintaining its zero interest rate policy until at least 2023. The Fed has also indicated that full employment and longer-term inflation averages are additional factors in considering any future rate hikes. This accommodative stance should continue to boost investor confidence and demand for yield in a low global rate environment. In addition, we believe the overall health of the consumer, strong housing market and expected inventory rebuilding provide support to our outlook.

The credit markets have been progressing through the cycle,² and we believe there are increasing signs of a shift towards recovery with corporate profits rebounding, easy monetary policy, balance sheet improvement and potential for large-scale vaccine distribution.

We have been maintaining a balance of liquidity, diversification and risk exposure in our portfolios. Within our credit allocation, we continue to focus on areas where we still see value based on our fundamental research. We are specifically focused on some of the sectors that were hardest hit by the pandemic including the transportation, recreational and hospitality industries. These areas of the economy include credits that have been cheap for their rating, have been able to access the capital markets for liquidity and are likely in a good position to benefit from the recovery.

Despite the higher valuations, we believe there are still selective opportunities in both the investment grade and high yield corporate sectors. Spreads have compressed but can potentially tighten further on improving fundamentals. We are selectively adding corporate credit, particularly in areas of the market that have lagged the recovery.

Our emerging market allocation largely represents US dollar-pay exposure to high quality securities with strong balance sheets and currently attractive real yields. We are holding little foreign currency but continue to evaluate opportunities in markets outside the US as we look for clarity on the outlook for global growth.

Market conditions in the past year have highlighted the notion that investors tend to overreact. The speed and severity of the recession and subsequent sharp rebound were unexpected, but also presented some favorable investment opportunities. These developments have served to reinforce our investment philosophy that markets are highly inefficient in the short term. We believe that we were able to capitalize on these developments in 2020 and that our portfolios are well-positioned to benefit from the expected economic growth and recovery in the new year.

During periods in which the US dollar appreciates relative to foreign currencies, funds that hold non-US-dollar-denominated bonds may realize currency losses in connection with the maturity or sale of certain bonds. These losses impact a fund’s ordinary income distributions (to the extent that losses are not offset by realized currency gains within the fund’s fiscal year). A recognized currency loss, in accordance with federal tax rules, decreases the amount of ordinary income a fund has available to distribute, even though these bonds continue to generate coupon income.

Fund officers have analyzed the Fund’s current portfolio of investments, realized currency gains and losses, schedule of maturities, and the corresponding amounts of unrealized currency losses that may become realized during the 2021 fiscal year. This analysis is performed regularly to determine how realized currency losses will impact periodic ordinary income distributions for the Fund. Based on the limited foreign currency exposures held by the Fund on the most recent quarterly analysis (as of December 31, 2020), Fund

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officers do not anticipate realized currency losses will have an impact on the distributions in the 2021 fiscal year. This analysis is based on certain assumptions including, but not limited to, the level of foreign currency exchange rates, security prices, interest rates, the Fund adviser’s ability to manage realized currency losses, and the net asset level of the Fund. Changes to these assumptions could materially impact the analysis and the amounts of future Fund distributions. Fund officers will continue to monitor these amounts on a regular basis and take the necessary actions required to manage the Fund’s distributions to address realized currency losses while seeking to avoid a return of capital distribution.

Hypothetical Growth of $100,000 Investment in Class Y Shares⁴

December 31, 2010 through December 31, 2020

See notes to chart on page 17.

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LOOMIS SAYLES STRATEGIC INCOME FUND

Average Annual Total Returns — December 31, 2020⁴

Performance data shown represents past performance and is no guarantee of, and not necessarily indicative of, future results. Total return and value will vary, and you may have a gain or loss when shares are sold. Current performance may be lower or higher than quoted. For most recent month-end performance, visit im.natixis.com. Performance for other share classes will be greater or less than shown based on differences in fees and sales charges. You may not invest directly in an index. Performance for periods less than one year is cumulative, not annualized. Returns reflect changes in share price and reinvestment of dividends and capital gains, if any. The table(s) do not reflect taxes shareholders might owe on any fund distributions or when they redeem their shares.

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ADDITIONAL INFORMATION

The views expressed in this report reflect those of the portfolio managers as of the dates indicated. The managers’ views are subject to change at any time without notice based on changes in market or other conditions. References to specific securities or industries should not be regarded as investment advice. Because the Funds are actively managed, there is no assurance that they will continue to invest in the securities or industries mentioned.

All investing involves risk, including the risk of loss. There is no assurance that any investment will meet its performance objectives or that losses will be avoided.

ADDITIONAL INDEX INFORMATION

This document may contain references to third party copyrights, indexes, and trademarks, each of which is the property of its respective owner. Such owner is not affiliated with Natixis Investment Managers or any of its related or affiliated companies (collectively “Natixis affiliates”) and does not sponsor, endorse or participate in the provision of any Natixis affiliates services, funds or other financial products.

The index information contained herein is derived from third parties and is provided on an “as is” basis. The user of this information assumes the entire risk of use of this information. Each of the third party entities involved in compiling, computing or creating index information, disclaims all warranties (including, without limitation, any warranties of originality, accuracy, completeness, timeliness, non-infringement, merchantability and fitness for a particular purpose) with respect to such information.

PROXY VOTING INFORMATION

A description of the Natixis Funds’ proxy voting policies and procedures is available without charge, upon request, by calling Natixis Funds at 800-225-5478; on Natixis Funds’ website at im.natixis.com; and on the Securities and Exchange Commission’s (SEC) website at www.sec.gov. Information regarding how Natixis Funds voted proxies relating to portfolio securities during the most recent 12-month period ended June 30 is available from Natixis Funds’ website and the SEC’s website.

QUARTERLY PORTFOLIO SCHEDULES

The Natixis Funds file a complete schedule of portfolio holdings with the SEC for the first and third quarters of each fiscal year as an exhibit to its reports on Form N-PORT. The Funds’ Form N-PORT reports are available on the SEC’s website at www.sec.gov. First and third quarter schedules of portfolio holdings are also available at im.natixis.com/funddocuments. A hard copy may be requested from the Fund at no charge by calling 800-225-5478.

CFA^® and Chartered Financial Analyst^® are registered trademarks owned by the CFA Institute.

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UNDERSTANDING FUND EXPENSES

As a mutual fund shareholder, you incur different costs: transaction costs, including sales charges (loads) on purchases and contingent deferred sales charges on redemptions, and ongoing costs, including management fees, distribution and/or service fees (12b-1 fees), and other fund expenses. Certain exemptions may apply. These costs are described in more detail in the Funds’ prospectuses. The following examples are intended to help you understand the ongoing costs of investing in the Funds and help you compare these with the ongoing costs of investing in other mutual funds.

The first line in the table of each class of Fund shares shows the actual account values and actual Fund expenses you would have paid on a $1,000 investment in the Fund from July 1, 2020 through December 31, 2020. To estimate the expenses you paid over the period, simply divide your account value by $1,000 (for example $8,600 account value divided by $1,000 = 8.60) and multiply the result by the number in the Expenses Paid During Period column as shown for your class.

The second line in the table for each class of Fund shares provides information about hypothetical account values and hypothetical expenses based on the Fund’s actual expense ratios and an assumed rate of return of 5% per year before expenses, which is not the Fund’s actual return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid on your investment for the period. You may use this information to compare the ongoing costs of investing in each Fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown reflect ongoing costs only, and do not include any transaction costs, such as sales charges. Therefore, the second line in the table of each Fund is useful in comparing ongoing costs only, and will not help you determine the relative costs of owning different funds. If transaction costs were included, total costs would be higher.

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BOARD APPROVAL OF THE INITIAL ADVISORY AGREEMENT FOR LOOMIS SAYLES INTERNATIONAL GROWTH FUND

The Investment Company Act of 1940, as amended (the “1940 Act”), requires that both the full Board of Trustees of the Trust (the “Board”) and a majority of the Trustees who are not “interested persons” (as defined in the 1940 Act) of the Trust (the “Independent Trustees”), voting separately, initially approve any new investment advisory agreements for a registered investment company, including a newly formed fund such as the Loomis Sayles International Growth Fund (the “Fund”). The Trustees, including the Independent Trustees, unanimously approved, for an initial two-year term, the proposed investment advisory agreement (the “Agreement”) for the Fund at a meeting held on December 3, 2020.

In connection with this review, Fund management and other representatives of the Fund’s adviser, Loomis, Sayles & Company, L.P. (the “Adviser”), distributed to the Trustees materials including, among other items, information regarding (i) the Fund’s investment objective, strategies and risks, (ii) the proposed advisory fee and other expenses to be charged to the Fund, including information comparing the Fund’s expenses to those of peer groups and categories of funds and the proposed expense cap, (iii) the size, education and experience of the Adviser’s investment staff and the investment strategies proposed to be used in managing the Fund, (iv) proposed arrangements for the distribution of the Fund’s shares, (v) information about the Adviser’s performance, and (vi) the general economic outlook with particular emphasis on the asset management industry.

The Trustees also considered the fact that they oversee other funds advised by the Adviser as well as information about the Adviser they had received in connection with their oversight of those other funds. Because the Fund is newly formed and had not commenced operations at the time of the Trustees’ review, certain information, including data relating to Fund performance, was not available, and therefore could not be distributed to the Trustees. Throughout the process, the Trustees were afforded the opportunity to ask questions of, and request additional materials from, the Adviser.

In considering whether to initially approve the Agreement, the Board, including the Independent Trustees, did not identify any single factor as determinative. Individual Trustees may have evaluated the information presented differently from one another, giving different weights to various factors. Matters considered by the Trustees, including the Independent Trustees, in connection with their approval of the Agreement included, but were not limited to, the factors listed below.

The nature, extent and quality of the services to be provided to the Fund under the Agreement. The Trustees considered the nature, extent and quality of the services to be provided by the Adviser and its affiliates to the Fund and the resources to be dedicated to the Fund by the Adviser and its affiliates. The Trustees considered their experience with other funds advised by the Adviser, as well as the affiliation between the Adviser and Natixis Investment Managers, LLC (“Natixis Investment Managers”), whose affiliates provide investment advisory services to other funds in the same family of mutual funds. In this regard, the Trustees considered not only the advisory services proposed to be provided by the Adviser to the Fund, but also the monitoring and oversight services proposed to be provided by Natixis Advisors, L.P. (“Natixis Advisors”). They also considered the administrative and shareholder services proposed to be provided by Natixis Advisors and its affiliates to the Fund.

The Trustees also considered the benefits to shareholders of investing in a mutual fund that is part of a family of funds that offers shareholders the right to exchange shares of one type of fund for shares of another type of fund, and provides a variety of fund and shareholder services.

After reviewing these and related factors, the Trustees concluded, within the context of their overall conclusions regarding the Agreement, that the scope of the services to be provided to the Fund under the Agreement seemed consistent with the Fund’s operational requirements, and that the Adviser had the capabilities, resources and personnel necessary to provide the advisory services that would be required by the Fund. The Trustees determined that the nature, extent and quality of services proposed to be provided under the Agreement supported approval of the Agreement.

Investment performance of the Fund and the Adviser. Because the Fund had not yet commenced operations, performance information for the Fund was not considered; however, the Board considered the performance of other funds managed by the Adviser.

The Trustees also considered the Adviser’s performance and reputation generally, the performance of the fund family generally, and the historical responsiveness of the Adviser to Trustee concerns about performance and the willingness of the Adviser to take steps intended to improve performance.

After reviewing these and related factors, the Trustees concluded, within the context of their overall conclusions regarding the Agreement, that these relevant factors supported approval of the Agreement.

The costs of the services to be provided by the Adviser and profits to be realized by the Adviser and its affiliates from their respective relationships with the Fund. Although the Fund had not yet commenced operations at the time of the Trustees’ review of the Agreement, the Trustees reviewed information comparing the proposed advisory fees and estimated total expenses of the Fund with the fees and expenses of comparable funds identified by the Adviser, including information about how those funds were selected and information about differences in such fees. In evaluating the Fund’s proposed advisory fee, the Trustees also took into account the demands,

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complexity and quality of the investment management of the Fund. The Trustees also noted that the Fund would have an expense cap in place. In addition, the Trustees considered information regarding the administrative and distribution fees to be paid by the Fund to the Adviser’s affiliates.

Because the Fund had not yet commenced operations, historical profitability information with respect to the Fund was not considered. However, the Trustees noted the information provided in court cases in which adviser profitability was an issue, the estimated expense level of the Fund, and that the Fund would be subject to an expense cap.

After reviewing these and related factors, the Trustees concluded, within the context of their overall conclusions regarding the Agreement, that the advisory fee and expenses proposed to be charged to the Fund were fair and reasonable, and supported the approval of the Agreement.

Economies of scale. The Trustees considered the extent to which the Adviser may realize economies of scale in the provision of services by the Adviser, and whether those economies could be shared with the Fund through breakpoints in its investment advisory fee or other means, such as expense caps. The Trustees noted that the Fund will be subject to an expense cap. After reviewing these and related factors, the Trustees concluded, within the context of their overall conclusions regarding the Agreement, that the extent to which economies of scale might be shared with the Fund supported the approval of the Agreement.

The Trustees also considered other factors, which included but were not limited to the following:

Based on their evaluation of all factors that they deemed to be material, including those factors described above, and assisted by the advice of independent counsel, the Trustees, including the Independent Trustees, concluded that the Agreement should be approved.

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Portfolio of Investments – as of December 31, 2020

Loomis Sayles High Income Fund

See accompanying notes to financial statements.

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Portfolio of Investments – as of December 31, 2020

Loomis Sayles High Income Fund – (continued)