fix(bedrock/thinking/websearch): beta headers, thinking fixes, API key loading, guardrails null safety

[Quentin-M]

Summary

Collection of production fixes developed and battle-tested against AWS Bedrock + Claude Opus 4.5/4.6 with extended thinking and websearch interception.

Supersedes #20470 and #20489 (closed without merging). Builds on the foundation of #19818 (merged). Related: #20488 (open — independently addresses the same websearch thinking blocks issue as 4630793, which is already merged).

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Bedrock: Centralize Beta Header Filtering

Problem: Inconsistent anthropic-beta header handling across the 3 Bedrock API paths:

• Invoke Chat used a whitelist (safe)
• Converse and Messages used blacklists via UNSUPPORTED_BEDROCK_CONVERSE_BETA_PATTERNS (allows unsupported headers through, causing AWS API errors in production)
• Adding new Claude models required updating multiple hardcoded lists

Fix: New litellm/llms/bedrock/beta_headers_config.py with centralized BedrockBetaHeaderFilter:

• Whitelist of 11 supported beta headers with version-based model restrictions
• Applied uniformly to all 3 Bedrock API paths (Invoke Chat, Converse, Messages)
• Zero maintenance for new Claude models — version-based rather than model-list-based
• Preserves advanced-tool-use → tool-search-tool + tool-examples translation for backward compatibility
• 40+ unit tests + 13 integration tests

Bedrock: Strip context_management from Request Body

Problem: context_management is enabled via the context-management-2025-06-27 anthropic-beta header, NOT as a request body parameter. Leaving it in the body causes "context_management: Extra inputs are not permitted" across all 3 Bedrock API paths.

Fix: Pop context_management from the request body in Converse, Invoke Chat, and Invoke Messages transformations.

Bedrock: Remove Invalid :0 Suffix from Claude Opus 4.6 Model ID

Problem: anthropic.claude-opus-4-6-v1:0 was present in BEDROCK_CONVERSE_MODELS but AWS Bedrock does not recognize this identifier. Only anthropic.claude-opus-4-6-v1 (without :0) is valid.

Fix: Remove the incorrect anthropic.claude-opus-4-6-v1:0 entry.

Cherry-picked from search_tools_fix branch (adapted from efec746a17).

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Thinking: Drop Thinking Param for Text-Only Assistant Messages

Problem: The existing fix (a494503f4b) only dropped the thinking param when the last assistant message had tool_calls without thinking blocks. When the last assistant message has plain text content (no tool_calls), the check returned False and thinking was not dropped, causing: "Expected thinking or redacted_thinking, but found text"

Fix:

• Add last_assistant_message_has_no_thinking_blocks() to detect assistant messages with content but no thinking blocks
• Extract shared _message_has_thinking_blocks() helper checking both thinking_blocks field and content array
• Apply fix to both Anthropic and Bedrock Converse transformations

Thinking: Recognize adaptive Type in is_thinking_enabled

Problem: is_thinking_enabled() only checked for type="enabled", but Claude Opus 4.6 uses type="adaptive". Without recognizing adaptive, max_tokens auto-adjustment didn't trigger, causing API errors.

Fix: Check thinking_type in ("enabled", "adaptive") in is_thinking_enabled().

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Websearch Interception: Load API Keys from Router Configuration

Problem: _execute_search() only extracted search_provider from the router's search_tools config, not api_key or api_base. This caused "TAVILY_API_KEY is not set" errors when keys are configured in the proxy YAML config rather than environment variables.

Fix: Extract api_key and api_base from the search tool's litellm_params and pass them to litellm.asearch(), with fallback to environment variables.

Note: The websearch thinking blocks preservation (4630793) and the max_tokens budget validation (12691dc) are already merged into main. This PR adds the missing API key loading fix on top.

Related: #14194, #20488

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Bedrock Guardrails: PII Redaction Null Safety

Problem: Multiple .get("key", []) calls in bedrock_guardrails.py can still return None when the AWS API returns explicit null for a field. This causes TypeError: 'NoneType' is not iterable in _redact_pii_matches() and _check_guardrail_blocked().

Fix: Add or [] fallback after each .get(...) call (9 locations).

Authored by Ryan Goldblatt, cherry-picked from search_tools_fix branch.

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Test Plan

• pytest tests/test_litellm/llms/bedrock/test_beta_headers_config.py -v
• pytest tests/test_litellm/llms/bedrock/test_anthropic_beta_support.py -v
• pytest tests/test_litellm/test_utils.py -v -k thinking
• pytest tests/test_litellm/proxy/guardrails/ -v
• Lint: make lint-ruff

All changes validated end-to-end: Claude Code → LiteLLM Proxy → AWS Bedrock → Claude Opus 4.5/4.6 with extended thinking and websearch.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview, Comment	Mar 17, 2026 4:12am

[greptile-apps]

Greptile Summary

This PR bundles several production fixes for AWS Bedrock + Claude Opus 4.5/4.6 deployments: centralised beta-header filtering via a new BedrockBetaHeaderFilter, context_management body-param stripping across all three Bedrock API paths, a model-ID correction for Opus 4.6, adaptive thinking-type recognition, guardrail null-safety, and websearch API-key loading from YAML config. Most of the fixes are well-executed and battle-tested. The one issue found:

• Dead code path for the "found text" thinking fix — The PR adds or last_assistant_message_has_no_thinking_blocks(messages) to the thinking-drop condition in both litellm/llms/anthropic/chat/transformation.py and litellm/llms/bedrock/chat/converse_transformation.py. However, the function has an internal guard (if not any_assistant_message_has_thinking_blocks(messages): return False) that is mutually exclusive with the outer condition's and not any_assistant_message_has_thinking_blocks(messages). When no prior thinking blocks exist (the scenario the fix targets), the function returns False; when prior thinking blocks do exist the outer guard prevents the drop. The result is that the new branch is permanently unreachable, and the "Expected thinking or redacted_thinking, but found text" error will continue to surface. The _message_has_thinking_blocks refactoring and the isolated unit tests are correct; the issue is only in how the function interacts with the call-site guard.
• All other fixes (centralized beta-header filtering, context_management stripping, is_thinking_enabled adaptive support, guardrail null-safety, websearch key loading) look correct and are well-tested.

Confidence Score: 3/5

• Safe to merge for all fixes except the thinking-drop path, which remains broken and will still surface "Expected thinking or redacted_thinking, but found text" at runtime.
• The PR ships many well-tested, clearly scoped fixes. One logic bug — the last_assistant_message_has_no_thinking_blocks dead code path — leaves a stated bug unfixed without surfacing a new error. All other changes are sound.
• litellm/utils.py (dead code path), litellm/llms/anthropic/chat/transformation.py, and litellm/llms/bedrock/chat/converse_transformation.py (both consume the broken function).

Important Files Changed

Filename	Overview
litellm/utils.py	Adds _message_has_thinking_blocks helper and last_assistant_message_has_no_thinking_blocks, but the new function has an internal guard that contradicts the outer condition, making the intended fix for "Expected thinking or redacted_thinking, but found text" a no-op.
litellm/llms/bedrock/beta_headers_config.py	New centralized whitelist-based beta header filter for all three Bedrock API paths; well-structured with version and family restrictions, thorough doc comments, and fixes noted in previous review rounds have been addressed.
litellm/llms/anthropic/chat/transformation.py	Adds last_assistant_message_has_no_thinking_blocks to the thinking-drop condition, but the new OR branch can never trigger due to the contradictory internal/outer guards (see utils.py comment).
litellm/llms/bedrock/chat/converse_transformation.py	Replaces ad-hoc blacklist filtering with the new centralized BedrockBetaHeaderFilter, strips context_management from the request body, and applies the same (dead-code) thinking-drop logic as the Anthropic path.
litellm/llms/bedrock/messages/invoke_transformations/anthropic_claude3_transformation.py	Removes hardcoded model-specific helpers, now correctly adds both tool-search-tool-2025-10-19 and tool-examples-2025-10-29 together before handing off to the centralized filter, and strips context_management from the body.
litellm/proxy/guardrails/guardrail_hooks/bedrock_guardrails.py	Straightforward null-safety fix adding or [] fallback after .get(...) calls to prevent TypeError: 'NoneType' is not iterable when AWS returns explicit null for policy fields.
litellm/integrations/websearch_interception/handler.py	Correctly extracts api_key and api_base from the search tool's litellm_params and passes them to litellm.asearch, fixing the TAVILY_API_KEY is not set error when keys are in YAML config rather than environment variables.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Incoming Request with thinking param] --> B{messages is not None?}
    B -- No --> Z[Keep thinking param]
    B -- Yes --> C{last_assistant_with_tool_calls\nhas_no_thinking_blocks?}

    C -- True --> D{not any_assistant_message\n_has_thinking_blocks?}
    C -- False --> E{last_assistant_message\n_has_no_thinking_blocks?}

    E -- True: only when some\nmessages have thinking --> D
    E -- False --> Z

    D -- True: no prior\nthinking exists --> F[Drop thinking param\n✅ works for tool_calls path]
    D -- False: prior thinking\nexists → BLOCKS DROP --> G["❌ last_assistant_message\npath is dead code\n(inner guard requires prior thinking;\nouter guard forbids prior thinking)"]

    G --> Z

    style G fill:#ffcccc,stroke:#cc0000
    style F fill:#ccffcc,stroke:#009900

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Comments Outside Diff (1)

1. litellm/utils.py, line 7677-7720 (link)

   New code path is dead — contradictory guards make fix a no-op

   last_assistant_message_has_no_thinking_blocks has an internal early-return that makes it impossible to ever trigger the thinking-drop at the call sites in anthropic/chat/transformation.py and bedrock/chat/converse_transformation.py.

   Trace through the two scenarios the PR targets:

   Scenario A — thinking never used before (the stated fix):

   messages = [user, assistant("Hello!"), user, assistant("Sure!")]
   thinking = {"type": "enabled"}  # first-time enable
   

   • any_assistant_message_has_thinking_blocks(messages) → False
   • The internal guard at line 7696 fires: if not any_assistant_message_has_thinking_blocks(messages): return False
   • last_assistant_message_has_no_thinking_blocks returns False
   • Outer condition: (False or False) and not False = False
   • Thinking NOT dropped → error "Expected thinking or redacted_thinking, but found text" still raised ❌

   Scenario B — thinking was used before, last message has no blocks:

   messages = [user, assistant[thinking+text], user, assistant("text")]
   

   • any_assistant_message_has_thinking_blocks(messages) → True (earlier message has thinking)
   • Internal guard passes; last_assistant_message_has_no_thinking_blocks returns True
   • Outer condition: (... or True) and not True = False (outer guard kills it)
   • Thinking NOT dropped ❌ (but dropping here would also break things — it would trigger "When thinking is disabled, an assistant message cannot contain thinking" for the earlier messages with thinking blocks)

   The internal guard (if not any_assistant_message_has_thinking_blocks(messages): return False) and the outer guard (and not any_assistant_message_has_thinking_blocks(messages)) are mutually exclusive — when one is satisfied the other is not — making the new or last_assistant_message_has_no_thinking_blocks(messages) branch permanently unreachable.

   The tests exercise the function in isolation and correctly document the expected return value, but no test exercises the full compound condition through transform_request / _transform_request_helper. A minimal end-to-end test would catch this:

   # Scenario A: enable thinking for the first time with a text-only history
   optional_params = {"thinking": {"type": "enabled"}}
   messages = [
       {"role": "user", "content": "hi"},
       {"role": "assistant", "content": "hello"},
   ]
   # After transformation, thinking should be dropped (with modify_params=True)
   # Currently it is NOT dropped, so the API call will fail.

   The likely fix is to remove the internal early-return inside last_assistant_message_has_no_thinking_blocks and let the outer and not any_assistant_message_has_thinking_blocks(messages) guard handle both branches uniformly, since that guard already prevents the dangerous Scenario B case.

_{Last reviewed commit: bdf1260}

[greptile-apps]

Hardcoded model-specific flags violate codebase convention

BETA_HEADER_MINIMUM_VERSION and BETA_HEADER_FAMILY_RESTRICTIONS encode model capability knowledge directly in code. Per the repo's own convention (see the custom instructions), model-specific capability flags should live in model_prices_and_context_window.json and be accessed via get_model_info / supports_* helpers — not hardcoded as Python dicts. This is exactly the same pattern the convention calls out as "BAD":

# BAD example from the convention
"interleaved-thinking-2025-05-14": 4.0,   # ← hardcoded version knowledge
"effort-2025-11-24": ["opus"],             # ← hardcoded family knowledge

The practical consequence is that each time Anthropic/AWS expands a beta flag to a new model generation, someone needs to update this file — the same maintenance burden the convention explicitly wants to avoid.

The intended good approach would be to consult get_model_info or a supports_* function (e.g., supports_reasoning, supports_computer_use) derived from model_prices_and_context_window.json, making the filter self-updating as model entries are added.

Rule Used: What: Do not hardcode model-specific flags in the ... (source)

_{Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!}

[Quentin-M]

Respectfully pushing back on this one. model_prices_and_context_window.json has no per-beta-header capability fields — it would require updating 100+ model entries every time AWS adds support for a new header. The version-based approach in BETA_HEADER_MINIMUM_VERSION is intentionally more maintainable: new Claude models require zero code changes, and only new capability restrictions (not expansions) need an entry. This is exactly the future-proof design called out in the module docstring.

[codspeed-hq]

Merging this PR will not alter performance

✅ 16 untouched benchmarks

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_{Comparing Quentin-M:fix/websearch-bedrock-thinking (bdf1260) with main (278c9ba)}