Amiga GL is an Amiga-friendly variant of GRASP GL animation format.
It is supported by a collection of utilities by John Bickers. It's not clear if that is the origin of the format.
There is some discussion of the format in the gl.man file from GL2P1.LZH (see below), section named "FROM MS-DOS TO AMIGA".
(More research needed.) The format seems similar to the original GRASP GL format, but with an extra four bytes at the beginning of the file. In the one available sample file, the first four bytes are
'A' 'G' 0x01 0x00.
- GL2P1.LZH → grasp/anim.gl