Are the GPIB commands of the 4287A compatible with the 4286A?

No, several GPIB commands of the 4287A are functionally different from the 4286A’s commands. To convert the 4286A GPIB commands of an existing program into appropriate GPIB commands of the 4287A, please refer to Appendix E "4286A vs. 4287A GPIB Commands Correspondence Table" in the 4287A Programming Manual.