Investment returns are exempt from Federal taxes.

Interest rate changes are among the most significant factors affecting bond return. When rates decline, bond prices rise and the fund may generate less income. When rates rise, bond prices fall. Depending on your tax situation, investment income may be subject to state and local taxes and the federal alternative minimum tax.

Even though the fund is designed to purchase assets exempt from federal taxes and currently has no exposure to the federal alternative minimum tax (AMT), there is no guarantee that all of the fund's income will be exempt from federal income tax or the federal AMT. Specifically, the portfolio managers are permitted at any time to invest up to 20% of the fund's assets in debt securities with interest payments that are subject to federal income tax and/or federal AMT.

Investment income may be subject to certain state and local taxes and, depending on your tax status, the federal alternative minimum tax (AMT). Capital gains are not exempt from state and federal income tax.

Fund shares are not guaranteed by the U.S. Government.

Please see the prospectus for details about sales charges.

The gross expense ratio is the fund's total annual operating costs, expressed as a percentage of the fund's average net assets for a given time period. It is gross of any fee waivers or expense reimbursement. The net expense ratio is the expense ratio after the application of any waivers or reimbursement. This is the actual ratio that investors paid during the fund's most recent fiscal year. Please see the prospectus for more information.

Investor Class Shares: Minimum initial investment is $1,000 for IRA and CESA accounts, and $2,500 for non-retirement accounts, but these minimums are waived with an initial investment of at least $500 per account and automatic investments of at least $100 per month. Non-Retirement Accounts: If your account balance falls below the minimum, or if you cancel your automatic monthly investment plan prior to reaching the minimum, American Century Investments may redeem the account and send the proceeds to you. Prior to doing so, we will notify you and give you 90 days to meet the minimum or reinstate your automatic monthly investment plan.

Only Investor Class shares are made available to investors directly. Advisor, A, C, I, and Y Classes of shares are only available for purchase by institutions or other financial intermediaries. R, R5, and R6 Classes of shares are only available for purchase by group employer-sponsored retirement plans. Review definitions and minimums for all share classes.

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