feat(types): add PostCompact hook event support

Add PostCompact hook event type, input, and specific output types
to match Claude Code CLI v2.1.76+. PostCompact fires after compact
operations complete, providing trigger type and compact summary.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: husniadil

src/claude_agent_sdk/__init__.py

@@ -50,6 +50,8 @@
     PermissionResultAllow,
     PermissionResultDeny,
     PermissionUpdate,
+    PostCompactHookInput,
+    PostCompactHookSpecificOutput,
     PostToolUseFailureHookInput,
     PostToolUseFailureHookSpecificOutput,
     PostToolUseHookInput,
@@ -403,6 +405,8 @@ async def call_tool(name: str, arguments: dict[str, Any]) -> Any:
     "StopHookInput",
     "SubagentStopHookInput",
     "PreCompactHookInput",
+    "PostCompactHookInput",
+    "PostCompactHookSpecificOutput",
     "NotificationHookInput",
     "SubagentStartHookInput",
     "PermissionRequestHookInput",

src/claude_agent_sdk/types.py

@@ -170,6 +170,7 @@ class PermissionResultDeny:
     | Literal["Stop"]
     | Literal["SubagentStop"]
     | Literal["PreCompact"]
+    | Literal["PostCompact"]
     | Literal["Notification"]
     | Literal["SubagentStart"]
     | Literal["PermissionRequest"]
@@ -273,6 +274,14 @@ class PreCompactHookInput(BaseHookInput):
     custom_instructions: str | None
 
 
+class PostCompactHookInput(BaseHookInput):
+    """Input data for PostCompact hook events."""
+
+    hook_event_name: Literal["PostCompact"]
+    trigger: Literal["manual", "auto"]
+    compact_summary: str
+
+
 class NotificationHookInput(BaseHookInput):
     """Input data for Notification hook events."""
 
@@ -308,6 +317,7 @@ class PermissionRequestHookInput(BaseHookInput, _SubagentContextMixin):
     | StopHookInput
     | SubagentStopHookInput
     | PreCompactHookInput
+    | PostCompactHookInput
     | NotificationHookInput
     | SubagentStartHookInput
     | PermissionRequestHookInput
@@ -354,6 +364,13 @@ class SessionStartHookSpecificOutput(TypedDict):
     additionalContext: NotRequired[str]
 
 
+class PostCompactHookSpecificOutput(TypedDict):
+    """Hook-specific output for PostCompact events."""
+
+    hookEventName: Literal["PostCompact"]
+    additionalContext: NotRequired[str]
+
+
 class NotificationHookSpecificOutput(TypedDict):
     """Hook-specific output for Notification events."""
 
@@ -381,6 +398,7 @@ class PermissionRequestHookSpecificOutput(TypedDict):
     | PostToolUseFailureHookSpecificOutput
     | UserPromptSubmitHookSpecificOutput
     | SessionStartHookSpecificOutput
+    | PostCompactHookSpecificOutput
     | NotificationHookSpecificOutput
     | SubagentStartHookSpecificOutput
     | PermissionRequestHookSpecificOutput

tests/test_tool_callbacks.py

@@ -744,6 +744,63 @@ async def pre_tool_hook(
         )
         assert result["hookSpecificOutput"]["permissionDecision"] == "allow"
 
+    @pytest.mark.asyncio
+    async def test_post_compact_hook_callback(self):
+        """Test that a PostCompact hook callback receives correct input and returns output."""
+        hook_calls: list[dict[str, Any]] = []
+
+        async def post_compact_hook(
+            input_data: HookInput, tool_use_id: str | None, context: HookContext
+        ) -> HookJSONOutput:
+            hook_calls.append({"input": input_data, "tool_use_id": tool_use_id})
+            return {
+                "hookSpecificOutput": {
+                    "hookEventName": "PostCompact",
+                    "additionalContext": "Compaction logged successfully",
+                }
+            }
+
+        transport = MockTransport()
+        query = Query(
+            transport=transport, is_streaming_mode=True, can_use_tool=None, hooks={}
+        )
+
+        callback_id = "test_post_compact_hook"
+        query.hook_callbacks[callback_id] = post_compact_hook
+
+        request = {
+            "type": "control_request",
+            "request_id": "test-post-compact",
+            "request": {
+                "subtype": "hook_callback",
+                "callback_id": callback_id,
+                "input": {
+                    "session_id": "sess-1",
+                    "transcript_path": "/tmp/t",
+                    "cwd": "/home",
+                    "hook_event_name": "PostCompact",
+                    "trigger": "auto",
+                    "compact_summary": "Conversation summary...",
+                },
+                "tool_use_id": None,
+            },
+        }
+
+        await query._handle_control_request(request)
+
+        assert len(hook_calls) == 1
+        assert hook_calls[0]["input"]["hook_event_name"] == "PostCompact"
+        assert hook_calls[0]["input"]["trigger"] == "auto"
+        assert hook_calls[0]["input"]["compact_summary"] == "Conversation summary..."
+
+        response_data = json.loads(transport.written_messages[-1])
+        result = response_data["response"]["response"]
+        assert result["hookSpecificOutput"]["hookEventName"] == "PostCompact"
+        assert (
+            result["hookSpecificOutput"]["additionalContext"]
+            == "Compaction logged successfully"
+        )
+
 
 class TestHookInitializeRegistration:
     """Test that new hook events can be registered through the initialize flow."""

tests/test_types.py

@@ -7,6 +7,8 @@
     NotificationHookSpecificOutput,
     PermissionRequestHookInput,
     PermissionRequestHookSpecificOutput,
+    PostCompactHookInput,
+    PostCompactHookSpecificOutput,
     ResultMessage,
     SubagentStartHookInput,
     SubagentStartHookSpecificOutput,
@@ -286,6 +288,34 @@ def test_permission_request_hook_input_with_suggestions(self):
         }
         assert len(hook_input["permission_suggestions"]) == 1
 
+    def test_post_compact_hook_input(self):
+        """Test PostCompactHookInput construction."""
+        hook_input: PostCompactHookInput = {
+            "session_id": "sess-1",
+            "transcript_path": "/tmp/transcript.jsonl",
+            "cwd": "/home/user/project",
+            "hook_event_name": "PostCompact",
+            "trigger": "auto",
+            "compact_summary": "Summary of the compacted conversation...",
+        }
+        assert hook_input["hook_event_name"] == "PostCompact"
+        assert hook_input["trigger"] == "auto"
+        assert (
+            hook_input["compact_summary"] == "Summary of the compacted conversation..."
+        )
+
+    def test_post_compact_hook_input_manual_trigger(self):
+        """Test PostCompactHookInput with manual trigger."""
+        hook_input: PostCompactHookInput = {
+            "session_id": "sess-2",
+            "transcript_path": "/tmp/transcript.jsonl",
+            "cwd": "/home/user/project",
+            "hook_event_name": "PostCompact",
+            "trigger": "manual",
+            "compact_summary": "User-initiated compaction summary",
+        }
+        assert hook_input["trigger"] == "manual"
+
 
 class TestHookSpecificOutputTypes:
     """Test hook-specific output type definitions."""
@@ -332,6 +362,15 @@ def test_post_tool_use_output_has_updated_mcp_tool_output(self):
         }
         assert output["updatedMCPToolOutput"] == {"result": "modified"}
 
+    def test_post_compact_hook_specific_output(self):
+        """Test PostCompactHookSpecificOutput construction."""
+        output: PostCompactHookSpecificOutput = {
+            "hookEventName": "PostCompact",
+            "additionalContext": "Compaction complete, summary logged",
+        }
+        assert output["hookEventName"] == "PostCompact"
+        assert output["additionalContext"] == "Compaction complete, summary logged"
+
 
 class TestMcpServerStatusTypes:
     """Test MCP server status type definitions."""