Summary
User reports Qwen3.8 Flash-Next running natively in NVFP4 under Basalt on an RTX 5090 at 400W with 128 GB of DDR5 RAM, giving 304 tok/s on structured output and 183 tok/s on prose.
Setup is Basalt with a .basalt pack that keeps stock NVIDIA experts and stores the dense layers as Q6_K; adding a peer RTX 5060 Ti raises the figures to 479 tok/s structured and 239 tok/s prose. Prefill reaches 8,582 tok/s on a 64K prompt, 7.6s to first token.
Against Infernix on the same NVFP4 weights and box the user claims up to 1.3x on decode and 1.6x on prefill. Quality versus Q8_0 over 100 chunks: PPL 3.308 (Q8_0 3.286), KLD 0.068, 91.5% same top-1.