64-Bit AMIBIOS 02.00.00 is a version of AMIBIOS for systems based on the Intel IA-64 architecture (such as ones with Itanium processors). As of July 2023, not much information regarding the version is known. The only known instances of the version can be seen on some SuperMicro motherboards for the Itanium processor (such as MBD-i2DML-8G2-O).
The version name
Although no exact name for the version is known (due to lack of photos and information), the BIOS file for the SuperMicro MBD-i2DML-8G2-O motherboard does contain a string mentioning "64-BIT AMI-BIOS" at offsets 43D250 and 43D260 when viewed with a binary viewer (such as HxD), along with a copyright date of 2003 on 43D270.
EFI shell
According to the user manual for the SuperMicro MBD-i2DML-8G2-O[1] the motherboard features an EFI Shell, which suggests despite the version name, 64-Bit AMIBIOS 02.00.00 must actually be an EFI firmware and not a BIOS firmware. As earliest known instance of AMI Aptio (AMI's commercial EFI firmware) is a beta release from 2005, 64-Bit AMIBIOS is probably the earliest EFI firmware made by AMI and is one of the earliest ever made, being made at least 4 years after Intel's release of the EFI firmware standard (in 1999).
It is likely AMI Aptio was based on 64-Bit AMIBIOS, which in turn is likely based on either AMIBIOS 8 or AMIBIOS 07.00.xx.