AMBC

Ambac Financial Group, Inc.

A financial services holding company that for decades guaranteed municipal bonds—backing the principal and interest that cities and states owed—Ambac was founded in 1971 in Milwaukee as the American Municipal Bond Assurance Corporation, whose initials spell its name. After later moving to New York, it sold its bond-guarantee business in 2025 and rebranded as Octave Specialty Group, now building specialty insurance firms across the U.S., U.K., and Bermuda.