Real FP4 Tensor-Core Code in Pure Rust on a Gaming GPU — with NVIDIA's Own Compiler

We report a viability result: an entire Llama-class decoder, written in pure Rust and compiled to PTX by NVIDIA's own experimental first-party Rust→PTX backend (cuda-oxide), runs FP4-quantized weights on a consumer NVIDIA RTX 5070 Ti and generates coherent English text. On a real TinyLlama-1.1B model quantized to MXFP4, the engine sustains roughly 181 tokens/s of decode throughput at steady state (median over a clean-GPU re-measurement; 188.6 tok/s in the original session, which the clean run reproduced) — within about 3.7×, or roughly 27%, of llama.cpp's decode throughput (≈664 tok/s, Q4_K_M, hand-tuned CUDA with CUDA graphs) on the same GPU, on a first, unoptimized cut. Along the way we measured the actual programmable surface of consumer Blackwell (sm_120) for Rust kernels and found it richer than secondary sources imply: TMA, thread-block clusters with distributed shared memory, and native FP4 block-scaled tensor-core MMA all execute, while the tcgen05 5th-generation tensor-memory MMA pipeline correctly does not. We do not claim supremacy; llama.cpp is faster today, and we say where and why. The contribution is that the path exists end to end — a coherent LLM, compiled from Rust by NVIDIA's compiler, on a gaming GPU — and that it lands close on the first attempt, with a clear optimization runway.