Introducing Structured Outputs in the API
OpenAI released Structured Outputs on Aug 6, 2024, making model outputs conform to developer-supplied JSON Schemas; `gpt-4o-2024-08-06` scored 100% on complex schema-following evals versus under 40% for `gpt-4-0613`. The feature is enabled with `strict: true` in function calling and works on tool-supporting models including `gpt-4-0613`, `gpt-3.5-turbo-0613`, and later. The key shift is constrained decoding plus schema training, not just valid JSON from JSON mode.
Why it matters: Structured Outputs makes models follow a developer's JSON Schema exactly, and the accuracy gap between new and old models shows why schema adherence is a model capability, not a prompt trick.