The Stack Below the Stack (Part 2): Below Python

The Stack Below the Stack , a 3-part series on how modern LLM inference actually works, told through a single DeepSeek V4 dtype bug. Part 1 · Physics of a request : why the first token is a different problem from every token after it, and why batching exists. Part 2 (this post) · Below Python : what actually runs under vllm serve , and why the escape hatches failed. Part 3 · Serving at scale :…