AMD Instinct MI455X OAM

The AMD Instinct MI455X is the frontier-AI member of the MI400 series and the accelerator behind the AMD Helios rackscale reference design, which combines 72 of them on Meta's Open Rack Wide standard. Built on 5th generation CDNA with up to 256 Work Group Processors, it uses stacked 3D hybrid-bonded compute dies on a CoWoS-L package with twelve stacks of HBM4 giving 432 GB at 23.3 TB/s. AMD publishes two peak figures for it, up to 40 PFLOPS of 4-bit and up to 20 PFLOPS of 8-bit, and both reconcile exactly against its own Helios aggregates: 72 GPUs give 2.9 exaFLOPS MXFP4, 1.4 exaFLOPS MXFP8, 31 TB of HBM4 and 1.67 PB/s, all four of which match. AMD names FP16, BF16 and INT8 as supported datatypes but publishes no rates for them; figures of 5,033 TFLOPS for FP16 and BF16, 20,133 for FP6 and 315 for FP32 are internally consistent with the published 8-bit peak but appear nowhere in AMD's material, so they are recorded here in prose rather than as specifications. AMD states no process node. It labels none of these figures dense or sparse, though it does describe CDNA as offering FP16 and BF16 sparsity support, and benchmarks these peaks against NVIDIA's dense NVFP4 datatype.