Enabling DeepSeek-V4-Flash Training on AMD Instinct MI355X GPUs with Primus

DeepSeek-AI released the DeepSeek-V4 series on April 24, 2026: a preview pair of MIT-licensed Mixture-of-Experts models, with DeepSeek-V4-Flash at 284B total parameters (13B activated) and a one-million-token context window. Flash pushes sparse attention further than any open-weight model before it: its 43 transformer layers interleave three different attention types, each layer sits inside a hyper-connection block rather than a plain residual, and every token is routed through 256 experts. Each of those choices breaks an assumption baked into stock Megatron-LM training code.