Build Your Own Engine

nano-vllm is the blueprint because it's the rare codebase small enough to read end to end and honest enough to contain the real ideas: prefix caching, tensor parallelism, CUDA graphs, in about 1.2k lines. Read it before writing a line of yours. Then resist copying it — the point of the build is discovering why each piece exists by needing it.

The details the probe grades were picked because that's where real engines leak: SSE framing with [DONE], usage accounting, max_tokens cutoffs, error shapes. Give per-request cancellation particular respect. A client disconnecting mid-stream has to free its KV blocks and leave the batch cleanly, and “streaming token generator with cancellation” shows up as a literal coding exercise at serving companies. This capstone also matters later: the flash-attention quest asks you to swap your own kernel into this engine and keep the probe green.