fix(anthropic): migrate output_format to output_config.format (GA API) by ropoctl · Pull Request #21635 · BerriAI/litellm

ropoctl · 2026-02-20T02:26:34Z

Anthropic's structured output API has graduated from beta:

output_format parameter moved to output_config.format
Beta headers (structured-outputs-2025-11-13) no longer required
Old beta header + output_format still work during transition period

Changes:

map_openai_params: store into output_config.format instead of output_format
update_headers: only add beta header for legacy output_format passthrough
Cosmetic: auto-formatted some long lines

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

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Please complete all items before asking a LiteLLM maintainer to review your PR

I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
My PR passes all unit tests on make test-unit
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<= 40 passing tests: unstable; be careful with your merges and assess the risk.

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Type

🆕 New Feature
🐛 Bug Fix
🧹 Refactoring
📖 Documentation
🚄 Infrastructure
✅ Test

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CLAassistant · 2026-02-20T02:26:40Z

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greptile-apps · 2026-02-20T02:30:08Z

Greptile Summary

Migrates Anthropic structured output from the beta API (output_format + structured-outputs-2025-11-13 header) to the GA API (output_config.format, no beta header required), while preserving backward-compatible passthrough of a user-supplied output_format key.

map_openai_params: uses setdefault(\"output_config\", {})[\"format\"] so a pre-existing effort key in output_config is preserved, and no output_format key is set.
update_headers: beta header is added only when output_format is still present (legacy direct passthrough); GA output_config.format requests go without it.
Tests are updated to verify the GA shape and two new tests cover the format+effort coexistence and an end-to-end transform_request check.

Confidence Score: 5/5

Safe to merge — the two-line production change is a straightforward field rename with no side effects, and the updated tests directly verify the new GA shape.

The production diff is minimal: one assignment changes which key is written in optional_params, and one condition narrows when the beta header is injected. Both directions are covered by existing plus new unit tests. The legacy output_format passthrough path is explicitly preserved, so direct callers who bypass map_openai_params are unaffected.

No files require special attention.

Important Files Changed

Filename	Overview
litellm/llms/anthropic/chat/transformation.py	Two-line change: `map_openai_params` now writes into `output_config.format` via `setdefault` (correctly preserving a pre-existing `effort` key), and `update_headers` drops the beta header for GA models while retaining it only for legacy `output_format` passthrough.
tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py	Existing tests updated to assert GA API shape (`output_config.format`, no beta header); two new tests added covering `output_config.format` + `effort` coexistence and end-to-end `transform_request` output.

_{Reviews (7): Last reviewed commit: "fix(anthropic): migrate output_format to..." | Re-trigger Greptile}

greptile-apps

_{1 file reviewed, 2 comments}

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greptile-apps · 2026-02-20T02:30:17Z

Additional Comments (1)

litellm/llms/anthropic/chat/transformation.py
the test at line 897 in test_anthropic_chat_transformation.py still expects output_format key, but now the code sets output_config.format instead

    # Should use output_config.format (native structured outputs)
    assert "output_config" in optional_params
    assert optional_params["output_config"]["format"]["type"] == "json_schema"

ropoctl · 2026-02-20T02:30:18Z

My apologies, the agent that wrote this ran black on the modified files, so there are unrelated whitespace/formatting changes. I will remove those if needed.

I verified the change with this script

#!/usr/bin/env -S uv run
# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "litellm @ <REDACTED0>",
#   "pydantic",
# ]
# ///
"""Test Anthropic structured output with output_config.format (GA API)."""
import os
import litellm
from pydantic import BaseModel

os.environ["ANTHROPIC_API_KEY"] = "<REDACTED1>"


class ExtractedInfo(BaseModel):
    name: str
    email: str
    plan_interest: str
    demo_requested: bool


response = litellm.completion(
    model="anthropic/claude-sonnet-4-20250514",
    api_base="<REDACTED2>",
    messages=[
        {
            "role": "user",
            "content": "Extract info: John Smith (john@example.com) wants Enterprise plan, demo next Tuesday 2pm.",
        }
    ],
    response_format=ExtractedInfo,
    max_tokens=1024,
)

print("=== Response ===")
print(response.choices[0].message.content)
print(f"\n=== Stop reason: {response.choices[0].finish_reason} ===")

# Validate it parses
parsed = ExtractedInfo.model_validate_json(response.choices[0].message.content)
print(f"\n=== Parsed ===")
print(f"Name: {parsed.name}")
print(f"Email: {parsed.email}")
print(f"Plan: {parsed.plan_interest}")
print(f"Demo: {parsed.demo_requested}")
print("\n✅ Anthropic structured output works!")

ropoctl · 2026-02-20T03:11:29Z

ptal @greptileai

greptile-apps

_{2 files reviewed, 5 comments}

_{Edit Code Review Agent Settings | Greptile}

greptile-apps · 2026-02-20T03:16:38Z

Additional Comments (3)

litellm/llms/anthropic/chat/transformation.py
method renamed to _is_claude_opus_4_6 but still called with old name _is_claude_4_6_model

            or AnthropicConfig._is_claude_opus_4_6(model)

litellm/llms/anthropic/chat/transformation.py
method renamed to _is_claude_opus_4_6 but still called with old name _is_claude_4_6_model

        if AnthropicConfig._is_claude_opus_4_6(model):

litellm/llms/anthropic/chat/transformation.py
method renamed to _is_claude_opus_4_6 but still called with old name _is_claude_4_6_model

                if effort == "max" and not self._is_claude_opus_4_6(model):

ropoctl · 2026-02-20T08:08:22Z

ptal @greptileai

greptile-apps

_{2 files reviewed, 1 comment}

_{Edit Code Review Agent Settings | Greptile}

greptile-apps · 2026-02-20T08:12:19Z

Additional Comments (1)

litellm/llms/anthropic/chat/transformation.py
missing opus_4.6 and opus_4_6 (underscore variants with dots). Other parts of the codebase check for these variants (e.g., bedrock/common_utils.py:486, bedrock/chat/converse_transformation.py:1280)

                        "opus-4.6",
                        "opus_4.6",
                        "opus-4-6",
                        "opus_4_6",
                        "sonnet-4.6",

ropoctl · 2026-02-20T15:40:21Z

Additional Comments (1)
litellm/llms/anthropic/chat/transformation.py missing opus_4.6 and opus_4_6 (underscore variants with dots). Other parts of the codebase check for these variants (e.g., bedrock/common_utils.py:486, bedrock/chat/converse_transformation.py:1280)
                        "opus-4.6",
                        "opus_4.6",
                        "opus-4-6",
                        "opus_4_6",
                        "sonnet-4.6",

pr no longer touches this, ptal @greptileai

ropoctl · 2026-02-25T07:01:25Z

@greptileai ptal

greptile-apps

_{2 files reviewed, no comments}

_{Edit Code Review Agent Settings | Greptile}

ropoctl · 2026-02-27T01:07:52Z

@ishaan-jaff would you be able to review this, please?

Arithmomaniac · 2026-04-19T08:02:51Z

@ropoctl know why your checks are failing?

ropoctl · 2026-04-19T13:36:01Z

@ropoctl know why your checks are failing?

it's flakes coming from files I didn't touch at all

ropoctl · 2026-07-10T21:15:57Z

@greptileai ptal

codecov · 2026-07-10T21:21:28Z

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

ropoctl · 2026-07-10T21:35:12Z

@greptileai ptal — rebased onto the required litellm_oss_staging base.

codspeed-hq · 2026-07-10T21:35:46Z

Merging this PR will not alter performance

✅ 31 untouched benchmarks

_{Comparing ropoctl:main (53838bd) with main (3d63eda)¹}

No successful run was found on litellm_oss_staging (6d796d0) during the generation of this report, so main (3d63eda) was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

Anthropic structured outputs are now GA. The beta `output_format` parameter has moved to `output_config.format`, and beta headers are no longer required. - Updated map_openai_params to set output_config.format instead of output_format - Legacy output_format passthrough still triggers the beta header - Updated and added tests verifying GA API structure and no beta header Ref: https://platform.claude.com/docs/en/build-with-claude/structured-outputs Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ropoctl · 2026-07-10T21:37:44Z

@greptileai ptal — updated the newer output_config.format regression test for GA no-beta-header behavior; full Anthropic transformation file passes (305 tests).

ropoctl · 2026-07-12T05:40:15Z

The CI red is because the targeted branch does not have #32643 yet

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ropoctl commented Feb 20, 2026

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Merging this PR will not alter performance

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