Intermediate45 min
Constrained Decoding: How to Get Guaranteed JSON from an LLM (and the Reasoning Tax)
How constrained decoding guarantees valid JSON from an LLM: runnable vLLM and structured-output examples, the latency cost, and the reasoning tax that JSON-mode hides.
Prerequisites
Python 3.10+vLLM 0.19+ and a GPU that can serve the model (or a smaller Qwen3.6 dense variant on a 24GB card)the datasets and pydantic libraries