Complete Claude 4.6 support alignment with compatibility aliases

[PeterDaveHello]

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• 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
  • make test-unit run hit a local litellm_enterprise editable-install mismatch (not related to this PR's changes). Focused validation tests passed: 123 passed.
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Type

🐛 Bug Fix
✅ Test

Changes

• Align Claude 4.6 model handling in Anthropic transformation logic:
  • recognize Sonnet 4.6 aliases (sonnet-4-6, sonnet_4_6, sonnet-4.6)
  • recognize dotted Opus 4.6 aliases (opus-4.6)
  • map reasoning_effort to adaptive thinking for Sonnet 4.6 (matching Opus 4.6 behavior)
  • keep output_config.effort=max restricted to Opus 4.6
• Align Bedrock Claude 4.6 regional model entries with canonical IDs while preserving compatibility aliases:
  • Opus 4.6: include jp and apac, and keep au alias for compatibility
  • Sonnet 4.6: include canonical jp and keep apac alias for compatibility
• Keep model price maps in sync:
  • model_prices_and_context_window.json
  • litellm/model_prices_and_context_window_backup.json
• Extend and minimally adjust focused tests:
  • tests/litellm/llms/anthropic/test_anthropic_reasoning_effort.py
  • tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py
  • tests/test_litellm/test_claude_opus_4_6_config.py

Validation run

Executed:

poetry run pytest tests/litellm/llms/anthropic/test_anthropic_reasoning_effort.py tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py tests/test_litellm/test_claude_opus_4_6_config.py

Result:

123 passed

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview, Comment	Feb 18, 2026 0:59am

[PeterDaveHello]

@greptileai

[greptile-apps]

Greptile Summary

This PR extends Claude 4.6 support by adding Sonnet 4.6 model detection and wiring it into the existing Anthropic transformation logic. Key changes:

• Adds _is_claude_sonnet_4_6() helper for detecting Sonnet 4.6 model aliases (sonnet-4-6, sonnet_4_6, sonnet-4.6)
• Adds dotted alias opus-4.6 to the existing Opus 4.6 detector
• Maps reasoning_effort to adaptive thinking for Sonnet 4.6, matching Opus 4.6 behavior
• Adds Sonnet 4.6 aliases to the native structured output (output_format) model list
• Correctly keeps effort='max' restricted to Opus 4.6 only
• Adds Bedrock regional entries (jp., apac.) for Opus 4.6 and Sonnet 4.6 in both pricing JSON files
• Extends tests thoroughly covering adaptive thinking, effort validation, and structured output for all new aliases

Confidence Score: 4/5

• This PR is safe to merge — it adds model aliases and routing logic with good test coverage and no behavioral regressions.
• The changes are well-scoped, follow existing patterns in the codebase, and include thorough test coverage (123 tests passing per the author). The transformation logic correctly restricts effort='max' to Opus 4.6 only while extending adaptive thinking to Sonnet 4.6. One minor style inconsistency noted in the response_format model list (underscore aliases only added for 4.6, not retroactively for 4.5), but this is pre-existing and low-risk.
• litellm/llms/anthropic/chat/transformation.py — core logic changes for model detection and routing.

Important Files Changed

Filename	Overview
litellm/llms/anthropic/chat/transformation.py	Adds _is_claude_sonnet_4_6 helper and wires Sonnet 4.6 into adaptive thinking and native structured output paths. Correctly restricts effort='max' to Opus 4.6 only. Adds underscore aliases for 4.6 models in response_format model set.
model_prices_and_context_window.json	Adds jp. and apac. regional entries for Opus 4.6 and jp. for Sonnet 4.6. Pricing and capabilities match existing regional entries for these models.
litellm/model_prices_and_context_window_backup.json	Backup file kept in sync with main model prices JSON. Same regional entries added.
tests/litellm/llms/anthropic/test_anthropic_reasoning_effort.py	Adds tests for Opus 4.6 dotted alias and Sonnet 4.6 adaptive thinking. All mock-only tests, no network calls.
tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_transformation.py	Extends structured output and effort validation tests to cover Sonnet 4.6. Adds test for reasoning_effort adaptive mapping for Sonnet 4.6. All tests are properly mocked.
tests/test_litellm/test_claude_opus_4_6_config.py	Updates region validation test to expect jp. and apac. entries in addition to existing au. alias. Adds Sonnet 4.6 regional registration assertions.

Flowchart

flowchart TD
    A[incoming model string] --> B{_is_claude_opus_4_6?}
    A --> C{_is_claude_sonnet_4_6?}
    
    B -->|Yes| D[adaptive thinking]
    C -->|Yes| D
    B -->|No| E{other reasoning model?}
    C -->|No| E
    E -->|Yes| F[budget-based thinking]
    E -->|No| G[no thinking param]

    A --> H{response_format check}
    H -->|model matches 4.5/4.6 set| I[native output_format]
    H -->|other model| J[tool-based workaround]

    A --> K{output_config.effort == max?}
    K -->|Yes| B2{_is_claude_opus_4_6?}
    B2 -->|Yes| L[allow max effort]
    B2 -->|No| M[raise ValueError]
    K -->|No| N[allow effort value]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Allow reasoning_effort for dotted Claude 4.6 aliases

This adds dotted alias handling to _map_reasoning_effort, but the normal completion flow validates params against get_supported_openai_params() before this mapping runs, and that list only includes reasoning_effort when supports_reasoning(model) is true. Because the Anthropic model map does not include claude-opus-4.6* / claude-sonnet-4.6* keys, those aliases still fail support detection and reasoning_effort is rejected as unsupported in utils._check_valid_arg, so the new dotted-alias reasoning mapping is unreachable in production requests.

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[PeterDaveHello]

Close due to #21448, opened a new #21487 to replace this one.