fix: preserve Anthropic thinking blocks and signatures in LiteLLM round-trip#4999
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giulio-leone wants to merge 4 commits intogoogle:mainfrom
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fix: preserve Anthropic thinking blocks and signatures in LiteLLM round-trip#4999giulio-leone wants to merge 4 commits intogoogle:mainfrom
giulio-leone wants to merge 4 commits intogoogle:mainfrom
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…nd-trip When using Claude models through LiteLLM, extended thinking blocks (with signatures) were lost after the first turn because: 1. _extract_reasoning_value() only read reasoning_content (flattened string without signatures), ignoring thinking_blocks 2. _content_to_message_param() set reasoning_content on the outgoing message, which LiteLLM's anthropic_messages_pt() template silently drops This fix: - Adds _is_anthropic_provider() helper to detect anthropic/bedrock/ vertex_ai providers - Updates _extract_reasoning_value() to prefer thinking_blocks (with per-block signatures) over reasoning_content - Updates _convert_reasoning_value_to_parts() to handle ChatCompletionThinkingBlock dicts, preserving thought_signature - Updates _content_to_message_param() to embed thinking blocks directly in the message content list for Anthropic providers, bypassing the broken reasoning_content path Fixes google#4801
Cover the model-driven LiteLLM Anthropic round-trip with a regression test.
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Summary
Fixes #4801 — Adaptive thinking is broken when using Claude models through LiteLLM.
Root Cause
When Claude produces extended thinking with
thinking_blocks(each containing atype,thinkingtext, andsignature), the round-trip through ADK's LiteLLM integration silently loses them:_extract_reasoning_value()only readreasoning_content(a flattened string without signatures), ignoring the richerthinking_blocksfield_content_to_message_param()setreasoning_contenton the outgoingChatCompletionAssistantMessage, but LiteLLM'santhropic_messages_pt()prompt template silently drops thereasoning_contentfield entirelyFix
Three coordinated changes in
lite_llm.py:_is_anthropic_provider()helperanthropic,bedrock,vertex_aiproviders_extract_reasoning_value()thinking_blocks(with per-block signatures) overreasoning_content_convert_reasoning_value_to_parts()ChatCompletionThinkingBlockdicts, preservingthought_signature_content_to_message_param()contentlist as{"type": "thinking", ...}dicts — this format passes through LiteLLM'santhropic_messages_pt()correctlyFor non-Anthropic providers (OpenAI, etc.), behavior is unchanged —
reasoning_contentis still used.Verification
anthropic_messages_pt()was tested to confirm:reasoning_contentfield → DROPPED (existing LiteLLM bug)contentas list with{"type": "thinking", ...}→ PRESERVED ✅Tests
Added 7 targeted tests covering:
_is_anthropic_provider()— provider detection_extract_reasoning_value()— prefersthinking_blocksoverreasoning_content_convert_reasoning_value_to_parts()— signature preservation from block dicts_convert_reasoning_value_to_parts()— plain string fallback (no signature)_content_to_message_param()— Anthropic: thinking blocks embedded in content list_content_to_message_param()— OpenAI: reasoning_content field used (unchanged)_content_to_message_param()— Anthropic thinking + tool calls combinedFull test suite: 4732 passed, 0 failures