Herein I'll try to maintain a full listing of changes between GM8.0 (800) and GM8.1 (810).
This information can kind of be gleaned by carefully reading the GM Release notes, and dumping the irrelevant junk.
http://store.yoyogames.com/downloads/gm4win/release-notes.htmlNote that, at this time, none of the changes in 810 affect the filesize. They have finally learned to recycle bytes. Also note that almost all of the changes are completely backwards compatible, meaning that if you change the version identifier back to 800, it will load in GM8.0, although some minor fields may have incorrect values (e.g. Font Range Min usually changed to 255).
8.1.X (oldest)Version identifier appearing after magic number changed from 800 to 810.
Font "Range Min" bytes now shared with Charset (default 0). First 2 bytes (little endian) still indicate Range Min. Next byte indicates charset identifier. Final byte reserved (0).
8.1.69Font "Range Min" and Charset bytes now merged with Anti-Aliasing (AA) selection (default 3). Final byte after the charset identifier now indicates the AA. 0 for Off, other values are 1, 2, and 3. Still uncertain what the different values of anti-aliasing mean.
Game Settings "Uninitialized variables" bytes now shared with "Throw an error when arguments aren't initialised correctly." (I abbreviate it as "Mismatched Arguments" or "Parameter Checking". Default On or 1). First byte is a bit-share, where Uninitialized Variables occupies &0x01, and Mismatched Arguments occupies &0x02.
8.1.71-91No known changes.
LGM is at this point.
8.1.106May have changed all strings, especially script code, to unicode support. Unconfirmed.
8.1.107-108No known format changes. Introduces new functions ansi_char(?), get_function_address(?), string_byte_length(?), string_byte_at(?).
8.1.109-123No known changes.
8.1.125May have changed the saved room settings format. Unconfirmed.
8.1.126-135No known changes.