The Pydantic Trap: Why Strict Structured Outputs Cause Silent Semantic Truncation in Production

Forcing LLMs to conform to deeply nested Pydantic schemas guarantees valid JSON syntax, but often causes silent semantic truncation and hallucinated null values on edge cases. Here is how Two-Phase Speculative Schema Decoding with AST repair solves it.

Written and maintained by Hassan Nazir, Forward Deployed Engineer and Applied AI practitioner.