fix: add support for thinking content blocks (anthropics#28)

## Summary

Fixes an issue where `thinking` content blocks in Claude Code responses
were not being parsed, resulting in empty `AssistantMessage` content
arrays.

## Changes
- Added `ThinkingBlock` dataclass to handle thinking content with
`thinking` and `signature` fields
- Updated client parsing logic in `_internal/client.py` to recognize and
create `ThinkingBlock` instances
- Added comprehensive test coverage for thinking block functionality

## Before

```python
# Claude Code response with thinking block resulted in:
AssistantMessage(content=[])  # Empty content!
```

## After

```python
# Now correctly parses to:
AssistantMessage(content=[
    ThinkingBlock(thinking="...", signature="...")
])
```

Fixes anthropics#27

---------

Co-authored-by: Dickson Tsai <dickson@anthropic.com>
Signed-off-by: Rushil Patel <rpatel@codegen.com>

Author: 2 people

src/claude_code_sdk/__init__.py

@@ -23,6 +23,7 @@
     ResultMessage,
     SystemMessage,
     TextBlock,
+    ThinkingBlock,
     ToolResultBlock,
     ToolUseBlock,
     UserMessage,
@@ -46,6 +47,7 @@
     "Message",
     "ClaudeCodeOptions",
     "TextBlock",
+    "ThinkingBlock",
     "ToolUseBlock",
     "ToolResultBlock",
     "ContentBlock",

src/claude_code_sdk/_internal/message_parser.py

@@ -11,6 +11,7 @@
     ResultMessage,
     SystemMessage,
     TextBlock,
+    ThinkingBlock,
     ToolResultBlock,
     ToolUseBlock,
     UserMessage,
@@ -53,6 +54,13 @@ def parse_message(data: dict[str, Any]) -> Message:
                                 user_content_blocks.append(
                                     TextBlock(text=block["text"])
                                 )
+                            case "thinking":
+                                user_content_blocks.append(
+                                    ThinkingBlock(
+                                        thinking=block["thinking"],
+                                        signature=block["signature"],
+                                    )
+                                )
                             case "tool_use":
                                 user_content_blocks.append(
                                     ToolUseBlock(
@@ -100,7 +108,9 @@ def parse_message(data: dict[str, Any]) -> Message:
                                 )
                             )
 
-                return AssistantMessage(content=content_blocks)
+                return AssistantMessage(
+                    content=content_blocks, model=data["message"]["model"]
+                )
             except KeyError as e:
                 raise MessageParseError(
                     f"Missing required field in assistant message: {e}", data

src/claude_code_sdk/types.py

@@ -47,6 +47,14 @@ class TextBlock:
     text: str
 
 
+@dataclass
+class ThinkingBlock:
+    """Thinking content block."""
+
+    thinking: str
+    signature: str
+
+
 @dataclass
 class ToolUseBlock:
     """Tool use content block."""
@@ -65,7 +73,7 @@ class ToolResultBlock:
     is_error: bool | None = None
 
 
-ContentBlock = TextBlock | ToolUseBlock | ToolResultBlock
+ContentBlock = TextBlock | ThinkingBlock | ToolUseBlock | ToolResultBlock
 
 
 # Message types
@@ -81,6 +89,7 @@ class AssistantMessage:
     """Assistant message with content blocks."""
 
     content: list[ContentBlock]
+    model: str
 
 
 @dataclass

tests/test_client.py

@@ -20,7 +20,9 @@ async def _test():
             ) as mock_process:
                 # Mock the async generator
                 async def mock_generator():
-                    yield AssistantMessage(content=[TextBlock(text="4")])
+                    yield AssistantMessage(
+                        content=[TextBlock(text="4")], model="claude-opus-4-1-20250805"
+                    )
 
                 mock_process.return_value = mock_generator()
 
@@ -43,7 +45,10 @@ async def _test():
             ) as mock_process:
 
                 async def mock_generator():
-                    yield AssistantMessage(content=[TextBlock(text="Hello!")])
+                    yield AssistantMessage(
+                        content=[TextBlock(text="Hello!")],
+                        model="claude-opus-4-1-20250805",
+                    )
 
                 mock_process.return_value = mock_generator()
 
@@ -83,6 +88,7 @@ async def mock_receive():
                         "message": {
                             "role": "assistant",
                             "content": [{"type": "text", "text": "Done"}],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
                     yield {

tests/test_integration.py

@@ -38,6 +38,7 @@ async def mock_receive():
                         "message": {
                             "role": "assistant",
                             "content": [{"type": "text", "text": "2 + 2 equals 4"}],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
                     yield {
@@ -103,6 +104,7 @@ async def mock_receive():
                                     "input": {"file_path": "/test.txt"},
                                 },
                             ],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
                     yield {
@@ -179,6 +181,7 @@ async def mock_receive():
                                     "text": "Continuing from previous conversation",
                                 }
                             ],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
 

tests/test_message_parser.py

@@ -142,7 +142,8 @@ def test_parse_valid_assistant_message(self):
                         "name": "Read",
                         "input": {"file_path": "/test.txt"},
                     },
-                ]
+                ],
+                "model": "claude-opus-4-1-20250805",
             },
         }
         message = parse_message(data)

tests/test_streaming_client.py

@@ -187,6 +187,7 @@ async def mock_receive():
                         "message": {
                             "role": "assistant",
                             "content": [{"type": "text", "text": "Hello!"}],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
                     yield {
@@ -229,6 +230,7 @@ async def mock_receive():
                         "message": {
                             "role": "assistant",
                             "content": [{"type": "text", "text": "Answer"}],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
                     yield {
@@ -250,6 +252,7 @@ async def mock_receive():
                                 {"type": "text", "text": "Should not see this"}
                             ],
                         },
+                        "model": "claude-opus-4-1-20250805",
                     }
 
                 mock_transport.receive_messages = mock_receive
@@ -335,6 +338,7 @@ async def mock_receive():
                         "message": {
                             "role": "assistant",
                             "content": [{"type": "text", "text": "Response 1"}],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
                     await asyncio.sleep(0.1)
@@ -531,13 +535,15 @@ async def mock_receive():
                         "message": {
                             "role": "assistant",
                             "content": [{"type": "text", "text": "Hello"}],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
                     yield {
                         "type": "assistant",
                         "message": {
                             "role": "assistant",
                             "content": [{"type": "text", "text": "World"}],
+                            "model": "claude-opus-4-1-20250805",
                         },
                     }
                     yield {

tests/test_types.py

@@ -5,7 +5,13 @@
     ClaudeCodeOptions,
     ResultMessage,
 )
-from claude_code_sdk.types import TextBlock, ToolResultBlock, ToolUseBlock, UserMessage
+from claude_code_sdk.types import (
+    TextBlock,
+    ThinkingBlock,
+    ToolResultBlock,
+    ToolUseBlock,
+    UserMessage,
+)
 
 
 class TestMessageTypes:
@@ -19,10 +25,20 @@ def test_user_message_creation(self):
     def test_assistant_message_with_text(self):
         """Test creating an AssistantMessage with text content."""
         text_block = TextBlock(text="Hello, human!")
-        msg = AssistantMessage(content=[text_block])
+        msg = AssistantMessage(content=[text_block], model="claude-opus-4-1-20250805")
         assert len(msg.content) == 1
         assert msg.content[0].text == "Hello, human!"
 
+    def test_assistant_message_with_thinking(self):
+        """Test creating an AssistantMessage with thinking content."""
+        thinking_block = ThinkingBlock(thinking="I'm thinking...", signature="sig-123")
+        msg = AssistantMessage(
+            content=[thinking_block], model="claude-opus-4-1-20250805"
+        )
+        assert len(msg.content) == 1
+        assert msg.content[0].thinking == "I'm thinking..."
+        assert msg.content[0].signature == "sig-123"
+
     def test_tool_use_block(self):
         """Test creating a ToolUseBlock."""
         block = ToolUseBlock(