MFS Active Short Muni Bond ETF (MFSX) is an exchange-traded fund in the Muni National Short category. It has $19.06M in assets and an expense ratio of 0.25%. MFS normally invests at least 80% of the fund’s net assets in municipal instruments, the interest on which is exempt from U.S. federal income tax. However, interest from the fund’s investments may be subject to the U.S. federal alternative minimum tax.