The Anton-class was a class X cruiser, a subclass of the Miranda-class, in service to Starfleet from the mid 23rd century and into the 24th century.
First launched in the 2230s and intended to supplement the Constitution-class heavy cruisers. However they were found to be lacking in certain key respects, most notably they were incapable of operating away from base for extended periods of time. This rendered them nearly useless in an exploration role. (FASA RPG modules: Federation Ship Recognition Manual, The Four Years War)