AMIBIOS "Rev-X2-03" (possibly also called AMIBIOS 2.03) is a version of AMIBIOS, assumed to be made by Access Methods Inc. (which then would sell the AMIBIOS code and trademark to American Megatrends). This version is assumed to be released in 1985 or early-1986.
The only known instance of it can be seen on an IBM XT clone motherboard (possibly this model, as the layout is similar) demonstrated in a YouTube video made by the user Dfgrt924[1]. This is believed to be the earliest known version of AMIBIOS with proof to confirm it's existence.
POST screen
The POST screen is different from all other known versions of AMIBIOS. It also has two memory test counters (with one being for base memory and other for expanded memory) instead of one as seen in other versions.
This version also lacks a BIOS identification string, with only the copyright and revision being shown where it would usually go. As AMIBIOS 2.2x already had one, the string may have been introduced with that.
It also lacks a setup key prompt, which indicates the BIOS does not have a built-in setup utility. This may also confirm it was released before 1987 (as the earliest known instances of AMIBIOS were released around that time). However, as built-in setups are rare on 8088 BIOSes overall (including on ones released after 1987), it may still have been released or at least compiled after that.
Error messages
There are two error messages seen in the video, and they are slightly different compared to the error messages seen on other versions of AMIBIOS.
Floppy drive not ready message:
Drive not ready
Insert diskette in A:
Press any key .....
Floppy drive boot failure message:
Boot failure
Insert diskette in A:
Press any key .....