feat: migrate Anthropic provider to native structured outputs API #263

cpsievert · 2026-01-06T15:53:03Z

Summary

Migrates Anthropic provider to use the new native structured outputs API (output_format parameter) for models that support it.

Uses new output_format parameter with beta client for supported models
Enables streaming with data_model for Claude 4.5 models (previously not supported)
Falls back to tool-based approach for older models
Adds model compatibility check (_supports_structured_outputs())

Supported models (new API)

claude-sonnet-4-5
claude-opus-4-1
claude-opus-4-5
claude-haiku-4-5

Key benefits

Streaming now works with data_model for supported models
Better validation via Anthropic's constrained decoding
Cleaner response format (JSON in text content instead of fake tool calls)

Documentation

https://platform.claude.com/docs/en/build-with-claude/structured-outputs

Test plan

Re-recorded VCR cassettes for data extraction tests
Verified streaming with data_model works
All 450 tests pass
Type checking passes

Note: This PR depends on #262

🤖 Generated with Claude Code

Use the new output_format parameter and beta client for models that support structured outputs (claude-sonnet-4-5, claude-opus-4-1, claude-opus-4-5, claude-haiku-4-5). This enables streaming with data_model for these models. Older models fall back to the previous tool-based approach. Documentation: https://platform.claude.com/docs/en/build-with-claude/structured-outputs 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

chatlas/_provider_anthropic.py

- Rename use_beta_structured_output to _supports_structured_outputs - Inline STRUCTURED_OUTPUT_MODELS into the function - Remove streaming fallback/warning for older models (let it fail) - Make create_data_model_tool a staticmethod - Revert unnecessary kwargs->api_kwargs rename in _token_count_args - Remove redundant comments about Beta API type signatures 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

- Move STRUCTURED_OUTPUTS_BETA and supports_structured_outputs after TYPE_CHECKING - Make supports_structured_outputs public (remove leading underscore) - Consolidate data_model handling into single block - Add TODO for removing legacy tool-based approach 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

chatlas/_provider_anthropic.py

cpsievert changed the base branch from feat/stream-data-model to main January 6, 2026 15:58

cpsievert force-pushed the feat/stream-structured-data branch 5 times, most recently from 1f65317 to 677a184 Compare January 6, 2026 16:31

cpsievert mentioned this pull request Jan 6, 2026

Stream structured data #238

Open

cpsievert force-pushed the feat/stream-structured-data branch from 677a184 to b268fe4 Compare January 6, 2026 16:35