DeepSeek shipped V4.1 Flash on Sep 10 with an unusual Causal Encoder-Decoder architecture and a $0.003/M off-peak cache-hit rate — about a tenth of what V4 Flash charged. The model has also absorbed V4 Pro's traffic from Sep 14. A working marketer's first-week take on what to hand it, what to keep on Opus 5 or the frontier tier, and where V4.1 Flash sits in the cache-heavy background stack.
