Semiannual June 30, 2021 Loomis Sayles High Income Fund Table of Contents Loomis Sayles Intermediate Municipal Bond Fund Portfolio Review 1 Portfolio of Investments 14 Loomis Sayles Investment Grade Bond Fund Financial Statements 64 Loomis Sayles Strategic Alpha Fund Notes to Financial Statements 92 Loomis Sayles Strategic Income Fund LOOMIS SAYLES HIGH INCOME FUND Managers Symbols Matthew J. Eagan, CFA® Class A NEFHX Brian P. Kennedy Class C NEHCX Elaine M. Stokes Class N LSHNX Todd P. Vandam, CFA® Class Y NEHYX Loomis, Sayles & Company, L.P. Investment Goal The Fund seeks high current income plus the opportunity for capital appreciation to produce a high total return. Average Annual Total Returns—June 30, 20213 Expense Ratios4 6 Months 1 Year 5 Years 10 Years Life of Class N Gross Net Class Y (Inception 2/29/08) NAV 3.28% 16.88% 6.89% 5.76% —% 0.98% 0.75% Class A (Inception 2/22/84) NAV 3.14 16.53 6.60 5.50 — 1.22 1.00 With 4.25% Maximum Sales Charge -1.18 11.46 5.67 5.04 — Class C (Inception 3/2/98) NAV 2.75 15.86 5.82 4.88 — 1.97 1.75 With CDSC1 1.75 14.86 5.82 4.88 — Class N (Inception 11/30/16) NAV 3.295 16.88 — — 6.52 0.88 0.70 Comparative Performance Bloomberg Barclays U.S. Corporate High-Yield Bond Index2 3.62 15.37 7.48 6.66 6.92 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. 1 Class C shares performance assumes a 1% CDSC applied when you sell shares within one year of purchase. 2 The Bloomberg Barclays U.S. Corporate High-Yield Bond Index measures the market of USD-denominated, non-investment grade, fixed-rate, taxable corporate bonds. Securities are classified as high yield if the middle rating of Moody’s, Fitch, and S&P is Ba1/BB+/BB+ or below, excluding emerging market debt. The Bloomberg Barclays U.S. Corporate High-Yield Bond Index was created in 1986, with history backfilled to July 1, 1983, and rolls up into the Bloomberg Barclays U.S. Universal and Global High-Yield Indices. Effective August 24, 2021, the index name was changed to Bloomberg U.S. Corporate High-Yield Bond Index. 3 Fund performance has been increased by fee waivers and/or expense reimbursements, if any, without which performance would have been lower. 4 Expense ratios are as shown in the Fund’s prospectus in effect as of the date of this report. The expense ratios for the current reporting period can be found in the Financial Highlights section of this report under Ratios to Average Net Assets. Net expenses reflect contractual expense limitations set to expire on 4/30/22. When a Fund’s expenses are below the limitation, gross and net expense ratios will be the same. See Note 6 of the Notes to Financial Statements for more information about the Fund’s expense limitations. 5 Generally accepted accounting principles require adjustments to be made to the net assets of the Fund for financial reporting purposes only, and as such, the total returns reflected above are different from the total returns reported in the financial highlights. The returns presented in the table above are what an investor would have actually experienced. 1 | LOOMIS SAYLES INTERMEDIATE MUNICIPAL BOND FUND Managers Symbols Dawn Mangerson Class A MIMAX James Grabovac, CFA® Class C MIMCX Lawrence Jones Class Y MIMYX Loomis, Sayles & Company, L.P. Investment Goal The Fund seeks a high level of federal tax-exempt current income, consistent with the preservation of capital. Average Annual Total Returns — June 30, 20214 Expense Ratios5 6 Months 1 Year 5 Years Life of Fund Gross Net Class Y (Inception 12/31/12)1 NAV 0.30% 2.64% 2.38% 2.61% 1.17% 0.46% Class A (Inception 12/31/12)1 NAV 0.17 2.38 2.13 2.33 1.43 0.71 With 3.00% Maximum Sales Charge -2.86 -0.67 1.51 1.96 Class C (Inception 12/31/12)1 NAV -0.20 1.62 1.37 1.62 2.18 1.46 With CDSC2 -1.19 0.62 1.37 1.62 Comparative Performance Bloomberg Barclays Municipal Bond Index3 1.06 4.17 3.25 3.53 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. 1 December 31, 2012 represents the date shares were first registered for public sale under the Securities Act of 1933. November 16, 2012 represents commencement of operations for accounting and financial reporting purposes only. 2 Performance for Class C shares assumes a 1.00% contingent deferred sales charge (“CDSC”) applied when you sell shares within one year of purchase. 3 Bloomberg Barclays Municipal Bond Index is a market value-weighted index of investment-grade municipal bonds with maturities of one year or more. Effective August 24, 2021, the index name was changed to Bloomberg Municipal Bond Index. 4 Fund performance has been increased by fee waivers and/or expense reimbursements, if any, without which performance would have been lower. 5 Expense ratios are as shown in the Fund’s prospectus in effect as of the date of this report. The expense ratios for the current reporting period can be found in the Financial Highlights section of this report under Ratios to Average Net Assets. Net expenses reflect contractual expense limitations set to expire on 4/30/22. When a Fund’s expenses are below the limitation, gross and net expense ratios will be the same. See Note 6 of the Notes to Financial Statements for more information about the Fund’s expense limitations. | 2 LOOMIS SAYLES INVESTMENT GRADE BOND FUND Managers Symbols Matthew J. Eagan, CFA® Class A LIGRX Brian P. Kennedy Class C LGBCX Elaine M. Stokes Class N LGBNX Loomis, Sayles & Company, L.P. Class Y LSIIX Admin Class LIGAX Investment Goal The Fund seeks high total investment return through a combination of current income and capital appreciation. Average Annual Total Returns — June 30, 20214 Expense Ratios5 6 Months 1 Year 5 Years 10 Years Life of Class N Gross Net Class Y (Inception 12/31/96) NAV 0.20% 5.97% 5.36% 4.60% —% 0.55% 0.50% Class A (Inception 12/31/96) NAV 0.08 5.71 5.10 4.33 — 0.80 0.75 With 4.25% Maximum Sales Charge -4.20 1.21 4.18 3.88 — Class C (Inception 9/12/03) NAV -0.30 4.97 4.31 3.71 — 1.55 1.50 With CDSC1 -1.29 3.98 4.31 3.71 — Class N (Inception 2/1/13) NAV 0.22 6.03 5.43 — 4.01 0.47 0.45 Admin Class (Inception 2/1/10) NAV -0.04 5.47 4.86 4.09 — 1.05 1.00 Comparative Performance Bloomberg Barclays U.S. Government/Credit Bond Index2 -1.96 -0.39 3.31 3.71 3.24 Bloomberg Barclays U.S. Aggregate Bond Index3 -1.60 -0.33 3.03 3.39 3.03 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. 1 Performance for Class C shares assumes a 1% contingent deferred sales charge (“CDSC”) applied when you sell shares within one year of purchase. 2 The Bloomberg Barclays U.S. Government/Credit Bond Index is the non-securitized component of the U.S. Aggregate Index and was the first macro index launched by Barclays Capital.