AMD's MI400 delivers 40 petaflops of MXFP4 compute

AMD detailed the MI400 at Hot Chips 2026: 40.26 petaflops of MXFP4 compute and 432GB of HBM4 per GPU, per ServeTheHome's writeup.

The MI400's peak MXFP4 throughput is four times the MI355X's, and per-GPU memory jumps from 288GB of HBM3E to 432GB of HBM4. More memory per GPU means fewer chips can hold a given model, which lowers hardware costs for teams building inference clusters.

At MXFP6 and MXFP8 the chip runs 20.13 petaflops each. It also holds 315 teraflops of vector FP16 and matrix FP32 for workloads that need full precision. Memory bandwidth per GPU is 23.3 TB/s.

Eight accelerator complex dies sit on TSMC's N2 process, with fabric, cache, and I/O split onto separate N3P dies. The chip totals 256 work group processors and 192MB of global L2 cache.

AMD's own benchmark claim centers on inference: 20 TB/s of measured MLA decode bandwidth in FP8. The company says that's 3.8x the MI355X's throughput at about 2.4x the energy efficiency. Decode bandwidth determines how fast a model streams tokens to a user, so this number matters more for inference workloads than the petaflops figure.

A 72-GPU Helios rack moves 1.7 PB/s. ServeTheHome's report doesn't say when MI400 systems ship or what they'll cost.