diff --git a/litellm/litellm_core_utils/prompt_templates/factory.py b/litellm/litellm_core_utils/prompt_templates/factory.py index 86cfbf70255..7a48bdfe102 100644 --- a/litellm/litellm_core_utils/prompt_templates/factory.py +++ b/litellm/litellm_core_utils/prompt_templates/factory.py @@ -2288,15 +2288,21 @@ def sanitize_messages_for_tool_calling( def _is_unsignable_thinking_block(block: object) -> bool: """A `thinking` block that Anthropic cannot accept on input. - Anthropic verifies the thinking signature cryptographically, so a block whose - signature is null, empty, or missing (e.g. from an open-source reasoning model) - is rejected with a 400 and must be dropped rather than blanked or repaired. - `redacted_thinking` blocks carry no signature and are always kept. + Anthropic verifies the signature cryptographically, so a block with a null, + empty, or missing signature (e.g. from an open-source reasoning model) is + rejected with a 400. It also rejects a `thinking` block whose text is empty + or whitespace-only ("each thinking block must contain thinking"), regardless + of signature, e.g. when a `thinking_blocks` history item from a non-Anthropic + reasoning provider is replayed through this path. `redacted_thinking` blocks + carry no signature and are always kept. """ if not isinstance(block, dict) or block.get("type") != "thinking": return False signature: Final = block.get("signature") - return not (isinstance(signature, str) and len(signature) > 0) + if not (isinstance(signature, str) and len(signature) > 0): + return True + thinking_text: Final = block.get("thinking") + return not (isinstance(thinking_text, str) and len(thinking_text.strip()) > 0) def _drop_unsignable_thinking_blocks( diff --git a/tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py b/tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py index 6265779b90d..7b3902ae3f4 100644 --- a/tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py +++ b/tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py @@ -3578,3 +3578,151 @@ async def test_bedrock_converse_pdf_only_user_message_gets_text_block_async(): assert len(result) == 1 assert any("document" in block for block in result[0]["content"]) assert _text_blocks(result[0]) == [BEDROCK_DOCUMENT_PLACEHOLDER_TEXT] + + +def test_anthropic_messages_pt_drops_empty_but_signed_thinking_block(): + """An empty-but-signed thinking block must still be dropped.""" + from litellm.litellm_core_utils.prompt_templates.factory import ( + anthropic_messages_pt, + ) + + messages = [ + {"role": "user", "content": "What's 2+2?"}, + { + "role": "assistant", + "content": "4", + "thinking_blocks": [ + { + "type": "thinking", + "thinking": "", + "signature": "sig_abc123_looks_valid", + } + ], + }, + ] + + result = anthropic_messages_pt( + messages=messages, + model="claude-sonnet-4-5-20250929", + llm_provider="anthropic", + ) + + assistant_msg = result[1] + assert isinstance(assistant_msg["content"], list) + content_types = [block.get("type") for block in assistant_msg["content"]] + assert "thinking" not in content_types, "empty-text thinking block must be dropped even though it has a signature" + + +def test_anthropic_messages_pt_keeps_non_empty_signed_thinking_block(): + """Regression: a non-empty, signed thinking block passes through unchanged.""" + from litellm.litellm_core_utils.prompt_templates.factory import ( + anthropic_messages_pt, + ) + + messages = [ + {"role": "user", "content": "What's 2+2?"}, + { + "role": "assistant", + "content": "4", + "thinking_blocks": [ + { + "type": "thinking", + "thinking": "Let me add these numbers together.", + "signature": "sig_abc123_looks_valid", + } + ], + }, + ] + + result = anthropic_messages_pt( + messages=messages, + model="claude-sonnet-4-5-20250929", + llm_provider="anthropic", + ) + + assistant_msg = result[1] + assert isinstance(assistant_msg["content"], list) + thinking_block = next((b for b in assistant_msg["content"] if b.get("type") == "thinking"), None) + assert thinking_block is not None, "non-empty signed thinking block must be kept" + assert thinking_block["thinking"] == "Let me add these numbers together." + assert thinking_block["signature"] == "sig_abc123_looks_valid" + + +def test_anthropic_messages_pt_keeps_redacted_thinking_block(): + """Regression: redacted_thinking blocks are unaffected by the emptiness check.""" + from litellm.litellm_core_utils.prompt_templates.factory import ( + anthropic_messages_pt, + ) + + messages = [ + {"role": "user", "content": "What's 2+2?"}, + { + "role": "assistant", + "content": "4", + "thinking_blocks": [ + { + "type": "redacted_thinking", + "data": "encrypted_opaque_blob", + } + ], + }, + ] + + result = anthropic_messages_pt( + messages=messages, + model="claude-sonnet-4-5-20250929", + llm_provider="anthropic", + ) + + assistant_msg = result[1] + assert isinstance(assistant_msg["content"], list) + content_types = [block.get("type") for block in assistant_msg["content"]] + assert "redacted_thinking" in content_types, "redacted_thinking blocks must always be kept" + + +def test_anthropic_messages_pt_drops_unsigned_thinking_block(): + """Regression: an unsigned thinking block is still dropped, regardless of text.""" + from litellm.litellm_core_utils.prompt_templates.factory import ( + anthropic_messages_pt, + ) + + messages = [ + {"role": "user", "content": "What's 2+2?"}, + { + "role": "assistant", + "content": "4", + "thinking_blocks": [ + { + "type": "thinking", + "thinking": "Let me add these numbers together.", + "signature": "", + } + ], + }, + ] + + result = anthropic_messages_pt( + messages=messages, + model="claude-sonnet-4-5-20250929", + llm_provider="anthropic", + ) + + assistant_msg = result[1] + assert isinstance(assistant_msg["content"], list) + content_types = [block.get("type") for block in assistant_msg["content"]] + assert "thinking" not in content_types, "unsigned thinking block must still be dropped" + + +def test_is_unsignable_thinking_block_treats_whitespace_only_as_empty(): + """Whitespace-only `thinking` text is treated as empty and dropped.""" + from litellm.litellm_core_utils.prompt_templates.factory import ( + _is_unsignable_thinking_block, + ) + + whitespace_only_block = { + "type": "thinking", + "thinking": " \n\t ", + "signature": "sig_abc123_looks_valid", + } + + assert _is_unsignable_thinking_block(whitespace_only_block) is True