tl;dr: DeepSeek 4.1 Flash delivers near-frontier performance (comparable to Claude Opus in daily coding use) at a fraction of the cost, enabled by a ~437x KV cache reduction that keeps all-day sessions under a dollar. The author argues Chinese labs are only a month or two behind OpenAI/Anthropic but operate on a fundamentally different cost structure—akin to generic drug makers skipping R&D—which threatens frontier labs' business model. Self-hosting still isn't economical, but the cost and efficiency gains make chasing top-tier models increasingly pointless for most workloads.