MI100 is hardly the first AMD datacenter GPU. The first Instinct branded card, MI25, is from 2017 [1]. But ATI/AMD had FirePro/FireStream branded GPGPU cards going back to the mid 2000s [2,3]. They just never caught on because AMD's software, support and marketing was not competitive with Nvidia's.
[1] https://www.techpowerup.com/gpu-specs/radeon-instinct-mi25.c...
[2] https://en.wikipedia.org/wiki/AMD_FireStream
[3] https://en.wikipedia.org/wiki/AMD_FirePro