Ambac Financial Group (Ambac) Financial Group, known as American Municipal Bond Assurance Corporation (Ambac), provides public and private financial guarantee products and solutions, such as bond insurance and other financial services, to customers from around the world, headquartered in Lower Manhattan, New York; ranked 1051 in the 2014 Global Corporate The company is headquartered in Lower Manhattan, New York, and ranked #1051 in the 2014 Global 2000.