Compatibility

• ZDR: eligible (excludes Covered Models)
• Supported models: claude-fable-5-1, claude-mythos-5-1, claude-fable-5, claude-mythos-5, claude-mythos-preview, claude-opus-5, claude-opus-4-8, claude-opus-4-7, claude-opus-4-6, claude-sonnet-5, claude-sonnet-4-6, claude-sonnet-4-5-20250929, claude-opus-4-5-20251101, claude-haiku-4-5-20251001
• Platforms: Claude API, Claude Platform on AWS, Amazon Bedrock [1], Google Cloud, Microsoft Foundry

1. On Amazon Bedrock, structured outputs are available for Claude Opus 4.6, Claude Sonnet 4.6, Claude Sonnet 4.5, Claude Opus 4.5, and Claude Haiku 4.5.

Structured outputs constrain Claude's responses to follow a specific schema, ensuring valid, parseable output for downstream processing. Structured outputs provide two complementary features:

• JSON outputs (output_config.format): Get Claude's response in a specific JSON format
• Strict tool use (strict: true): Guarantee schema validation on tool names and inputs

You can use these features independently or together in the same request.

Migrating from beta? The output_format parameter has moved to output_config.format, and beta headers are no longer required. The API continues to accept the old beta header (structured-outputs-2025-11-13) and the output_format request field for a transition period, but the Python SDK (v1.0 and later) does not accept output_format=\{...\} on client.beta.messages.create() or count_tokens() and raises a TypeError; use output_config instead. See the following code examples for the updated API shape.