AN2 (short for ANSI/2, though it's unlikely its creators were authorized to use such a name) is an extension of ANSI Art format. It defines new escape codes to support customizing the palette and font. It does not appear to have caught on.
AN2 is not backward-compatible with ANSI Art. An ANSI Art viewer lacking AN2 support will probably display a lot of garbage characters when rendering an AN2 file.