AMD Instinct MI455X

The AMD Instinct MI455X is the frontier-AI member of the MI400 series and the accelerator behind the AMD Helios rackscale design, which puts 72 of them in a rack on the Open Rack Wide standard. It is built on 5th Gen AMD CDNA with 256 compute units across eight compute dies and two I/O dies on TSMC 2nm and 3nm, clocked up to 2.4 GHz, with twelve stacks of HBM4 giving 432 GB at 23.3 TB/s. AMD packages four liquid-cooled MI455X GPUs on an enhanced accelerator module (EAM) rather than the OAM of earlier Instinct parts. The datasheet rates it at 40,265 TFLOPS of OCP MXFP4, 20,133 of MXFP6, MXFP8 and FP8, and 5,033 of matrix FP16, BF16 and INT8, all dense, with structured sparsity doubling only the last three. FP8 runs at four times FP16, not the usual two, because the generation quadrupled 8-bit throughput per compute unit while doubling 16-bit. FP32 is 315 TFLOPS and FP64 only 5, which is the clearest sign that this part was cut for AI and that HPC belongs to the MI430X. Each GPU gets 3.6 TB/s of UALink over Ethernet scale-up, 600 GB/s of scale-out and a 256 GB/s Infinity Fabric link to its EPYC Venice host.