DeepSeek V4 dropped, the benchmarks looked aggressive, and the price-per-million-tokens looked even more aggressive. The first thing I wanted to know wasn't "is it as good as Claude Opus 4.6 or GPT-5.4?" — it was "can my actual coding agents use it without me rewriting half my workflow?" Because that's the part nobody benchmarks. A model can be the cheapest reasoner on the leaderboard and still be useless to me if Claude Code, Codex CLI, and Gemini CLI can't talk to it the way they expect to. Here's what I learned getting DeepSeek V4 into a real AI coding workflow without forking any of the CLIs. The protocol problem nobody warns you about Every AI coding tool has hard-coded assumptions about which API protocol it speaks: Claude Code speaks Anthropic's Messages API. It expects x-api-key , anthropic-version , content blocks, cache_control , the whole shape. Codex CLI speaks OpenAI's Responses API. It expects Authorization: Bearer , tools , tool_choice , streaming SSE in OpenAI's specific format.…