diff --git a/src/agentkit/calendar/extraction.py b/src/agentkit/calendar/extraction.py
new file mode 100644
index 0000000..41ac0d5
--- /dev/null
+++ b/src/agentkit/calendar/extraction.py
@@ -0,0 +1,129 @@
+"""Post-processing extraction of schedule info from conversation text.
+
+Two-stage approach (U4):
+1. Zero-LLM regex keyword gate — skip LLM entirely if no time-related keywords.
+2. LLM extraction — call the LLM gateway to pull structured event data.
+
+Extracted events are persisted via ``CalendarService.create_event`` with
+``source="post_extract"`` and the originating ``conversation_id`` for
+traceability (R15).
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import re
+
+from agentkit.calendar.service import CalendarService
+
+logger = logging.getLogger(__name__)
+
+
+class PostProcessingExtractor:
+    """Extract schedule info from conversation text after a chat turn.
+
+    Two-stage: regex keyword gate (zero LLM) → LLM extraction.
+    """
+
+    # Time-related keywords that trigger LLM extraction
+    _KEYWORD_RE = re.compile(
+        r"明天|后天|下周|本周|今天下午|今天上午|上午|下午|晚上|"
+        r"\d+点|\d+月\d+日|\d+号|开会|截止|deadline|schedule|"
+        r"reminder|提醒|预约|约定|安排",
+        re.IGNORECASE,
+    )
+
+    def __init__(self, calendar_service: CalendarService, llm_gateway=None):
+        self.service = calendar_service
+        self.llm_gateway = llm_gateway  # Optional, may be set later
+
+    async def extract(
+        self,
+        conversation_text: str,
+        conversation_id: str,
+        user_id: str,
+    ) -> list[dict]:
+        """Extract events from conversation text.
+
+        Returns list of created event dicts. Empty if no keywords or no events extracted.
+        Never raises — all failures are logged and swallowed.
+        """
+        # 1. Keyword gate — zero LLM cost if no match
+        if not self._KEYWORD_RE.search(conversation_text):
+            return []
+
+        # 2. LLM extraction
+        events_data = await self._llm_extract(conversation_text)
+        if not events_data:
+            return []
+
+        # 3. Create events with source="post_extract"
+        created = []
+        for event_data in events_data:
+            try:
+                event = await self.service.create_event(
+                    user_id=user_id,
+                    title=event_data.get("title", ""),
+                    start_time=event_data.get("start_time", ""),
+                    end_time=event_data.get("end_time", ""),
+                    description=event_data.get("description", ""),
+                    source="post_extract",
+                    conversation_id=conversation_id,
+                )
+                created.append(event.to_dict())
+            except Exception as e:
+                logger.warning(f"Failed to create extracted event: {e}")
+                continue
+
+        return created
+
+    async def _llm_extract(self, text: str) -> list[dict]:
+        """Call LLM gateway to extract events from text.
+
+        Returns list of event dicts: [{title, start_time, end_time, description}].
+        Returns [] on any error or empty result.
+        """
+        if self.llm_gateway is None:
+            return []
+
+        prompt = self._build_extraction_prompt(text)
+        try:
+            response = await self.llm_gateway.acomplete(
+                messages=[{"role": "user", "content": prompt}],
+                temperature=0.1,
+            )
+            return self._parse_llm_response(response)
+        except Exception as e:
+            logger.warning(f"LLM extraction failed: {e}")
+            return []
+
+    def _build_extraction_prompt(self, text: str) -> str:
+        """Build the LLM extraction prompt."""
+        return f"""Extract schedule/event information from the following conversation text.
+Return a JSON array of events. Each event should have: title, start_time (ISO 8601), end_time (ISO 8601), description.
+If no events are found, return an empty array [].
+
+Conversation text:
+{text}
+
+Respond with ONLY the JSON array, no other text."""
+
+    def _parse_llm_response(self, response: str) -> list[dict]:
+        """Parse LLM response as JSON array. Returns [] on any error."""
+        try:
+            # Strip markdown code fences if present
+            cleaned = response.strip()
+            if cleaned.startswith("```"):
+                cleaned = cleaned.split("\n", 1)[1] if "\n" in cleaned else cleaned[3:]
+            if cleaned.endswith("```"):
+                cleaned = cleaned[:-3]
+            cleaned = cleaned.strip()
+
+            data = json.loads(cleaned)
+            if not isinstance(data, list):
+                return []
+            return [item for item in data if isinstance(item, dict) and "title" in item]
+        except (json.JSONDecodeError, TypeError) as e:
+            logger.warning(f"Failed to parse LLM response as JSON: {e}")
+            return []
diff --git a/tests/unit/calendar/test_extraction.py b/tests/unit/calendar/test_extraction.py
new file mode 100644
index 0000000..6f0d17f
--- /dev/null
+++ b/tests/unit/calendar/test_extraction.py
@@ -0,0 +1,385 @@
+"""Tests for PostProcessingExtractor (U4)."""
+
+from __future__ import annotations
+
+import asyncio
+import json
+from pathlib import Path
+
+import pytest
+
+from agentkit.calendar.db import init_calendar_db
+from agentkit.calendar.extraction import PostProcessingExtractor
+from agentkit.calendar.service import CalendarService
+
+
+# ---------------------------------------------------------------------------
+# Fixtures
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture
+def calendar_db_path(tmp_path: Path) -> Path:
+    path = tmp_path / "test_calendar.db"
+    asyncio.run(init_calendar_db(path))
+    return path
+
+
+@pytest.fixture
+def service(calendar_db_path: Path) -> CalendarService:
+    return CalendarService(db_path=calendar_db_path)
+
+
+@pytest.fixture
+def extractor(service: CalendarService) -> PostProcessingExtractor:
+    return PostProcessingExtractor(calendar_service=service)
+
+
+class MockLLMGateway:
+    """Minimal async mock for the LLM gateway."""
+
+    def __init__(self, response: str) -> None:
+        self.response = response
+        self.called = False
+        self.call_count = 0
+
+    async def acomplete(self, messages, temperature: float = 0.1) -> str:
+        self.called = True
+        self.call_count += 1
+        return self.response
+
+
+# ---------------------------------------------------------------------------
+# Keyword regex gate
+# ---------------------------------------------------------------------------
+
+
+def test_keyword_regex_matches_chinese_time_words(extractor: PostProcessingExtractor) -> None:
+    """Chinese time words trigger the keyword gate."""
+    assert extractor._KEYWORD_RE.search("明天下午3点开会") is not None
+    assert extractor._KEYWORD_RE.search("后天截止") is not None
+    assert extractor._KEYWORD_RE.search("下周安排一下") is not None
+    # No time words — should not match
+    assert extractor._KEYWORD_RE.search("继续优化吧") is None
+    assert extractor._KEYWORD_RE.search("好的，没问题") is None
+
+
+def test_keyword_regex_matches_english_time_words(extractor: PostProcessingExtractor) -> None:
+    """English time words trigger the keyword gate (case-insensitive)."""
+    assert extractor._KEYWORD_RE.search("deadline tomorrow") is not None
+    assert extractor._KEYWORD_RE.search("Schedule a meeting") is not None
+    assert extractor._KEYWORD_RE.search("set a reminder") is not None
+    # No time words — should not match
+    assert extractor._KEYWORD_RE.search("hello world") is None
+    assert extractor._KEYWORD_RE.search("how are you") is None
+
+
+# ---------------------------------------------------------------------------
+# Keyword gate skips LLM
+# ---------------------------------------------------------------------------
+
+
+async def test_no_keyword_skips_llm_call(
+    extractor: PostProcessingExtractor, service: CalendarService
+) -> None:
+    """No keyword in text → LLM gateway never called, returns []."""
+    gateway = MockLLMGateway(response="[]")
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="好的，我们继续优化代码吧",
+        conversation_id="conv-1",
+        user_id="user-1",
+    )
+
+    assert result == []
+    assert gateway.called is False
+    assert gateway.call_count == 0
+
+
+# ---------------------------------------------------------------------------
+# Keyword hit triggers LLM extraction
+# ---------------------------------------------------------------------------
+
+
+async def test_keyword_hit_triggers_llm_extraction(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """Keyword present → LLM called → event created with source='post_extract'."""
+    llm_response = json.dumps(
+        [
+            {
+                "title": "团队会议",
+                "start_time": "2026-07-01T10:00:00+00:00",
+                "end_time": "2026-07-01T11:00:00+00:00",
+                "description": "周会",
+            }
+        ]
+    )
+    gateway = MockLLMGateway(response=llm_response)
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="明天下午3点开个会",
+        conversation_id="conv-42",
+        user_id="user-1",
+    )
+
+    assert gateway.called is True
+    assert gateway.call_count == 1
+    assert len(result) == 1
+    event = result[0]
+    assert event["title"] == "团队会议"
+    assert event["source"] == "post_extract"
+    assert event["start_time"] == "2026-07-01T10:00:00+00:00"
+    assert event["end_time"] == "2026-07-01T11:00:00+00:00"
+    assert event["description"] == "周会"
+
+
+# ---------------------------------------------------------------------------
+# LLM returns empty array
+# ---------------------------------------------------------------------------
+
+
+async def test_llm_returns_empty_array_creates_nothing(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """LLM returns [] → no events created."""
+    gateway = MockLLMGateway(response="[]")
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="明天有个安排",
+        conversation_id="conv-1",
+        user_id="user-1",
+    )
+
+    assert result == []
+    assert gateway.called is True
+
+
+# ---------------------------------------------------------------------------
+# Malformed LLM response
+# ---------------------------------------------------------------------------
+
+
+async def test_malformed_llm_response_handled_gracefully(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """Invalid JSON response → no crash, returns []."""
+    gateway = MockLLMGateway(response="this is not json at all")
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="明天开会",
+        conversation_id="conv-1",
+        user_id="user-1",
+    )
+
+    assert result == []
+
+
+async def test_malformed_llm_response_json_object_not_array(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """JSON object (not array) → treated as no events."""
+    gateway = MockLLMGateway(response='{"title": "会议"}')
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="明天开会",
+        conversation_id="conv-1",
+        user_id="user-1",
+    )
+
+    assert result == []
+
+
+# ---------------------------------------------------------------------------
+# conversation_id traceability
+# ---------------------------------------------------------------------------
+
+
+async def test_extracted_events_have_conversation_id(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """Extracted events carry the conversation_id for traceability."""
+    llm_response = json.dumps(
+        [
+            {
+                "title": "评审会",
+                "start_time": "2026-07-01T14:00:00+00:00",
+                "end_time": "2026-07-01T15:00:00+00:00",
+                "description": "",
+            }
+        ]
+    )
+    gateway = MockLLMGateway(response=llm_response)
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="后天下午2点评审会",
+        conversation_id="conv-trace-99",
+        user_id="user-7",
+    )
+
+    assert len(result) == 1
+    assert result[0]["conversation_id"] == "conv-trace-99"
+    assert result[0]["user_id"] == "user-7"
+
+
+# ---------------------------------------------------------------------------
+# Async / non-blocking
+# ---------------------------------------------------------------------------
+
+
+async def test_extraction_does_not_block_chat_response(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """extract() is awaitable and returns a list (inherent async guarantee)."""
+    gateway = MockLLMGateway(response="[]")
+    extractor.llm_gateway = gateway
+
+    # Awaiting must yield a list, not a coroutine or other object.
+    result = await extractor.extract(
+        conversation_text="明天deadline",
+        conversation_id="conv-1",
+        user_id="user-1",
+    )
+    assert isinstance(result, list)
+
+
+# ---------------------------------------------------------------------------
+# No LLM gateway configured
+# ---------------------------------------------------------------------------
+
+
+async def test_no_llm_gateway_returns_empty(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """llm_gateway=None + keyword hit → returns [] without error."""
+    assert extractor.llm_gateway is None
+
+    result = await extractor.extract(
+        conversation_text="明天开会",
+        conversation_id="conv-1",
+        user_id="user-1",
+    )
+
+    assert result == []
+
+
+# ---------------------------------------------------------------------------
+# Code-fenced LLM response
+# ---------------------------------------------------------------------------
+
+
+async def test_llm_response_with_code_fences_parsed(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """LLM wraps JSON in ```json ... ``` fences → parsed correctly."""
+    payload = json.dumps(
+        [
+            {
+                "title": "站会",
+                "start_time": "2026-07-01T09:00:00+00:00",
+                "end_time": "2026-07-01T09:15:00+00:00",
+                "description": "每日站会",
+            }
+        ]
+    )
+    fenced = f"```json\n{payload}\n```"
+    gateway = MockLLMGateway(response=fenced)
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="明天上午开站会",
+        conversation_id="conv-1",
+        user_id="user-1",
+    )
+
+    assert len(result) == 1
+    assert result[0]["title"] == "站会"
+    assert result[0]["description"] == "每日站会"
+
+
+# ---------------------------------------------------------------------------
+# Multiple events
+# ---------------------------------------------------------------------------
+
+
+async def test_multiple_events_extracted(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """LLM returns 3 events → 3 events created."""
+    llm_response = json.dumps(
+        [
+            {
+                "title": "会议A",
+                "start_time": "2026-07-01T09:00:00+00:00",
+                "end_time": "2026-07-01T10:00:00+00:00",
+                "description": "",
+            },
+            {
+                "title": "会议B",
+                "start_time": "2026-07-02T14:00:00+00:00",
+                "end_time": "2026-07-02T15:00:00+00:00",
+                "description": "",
+            },
+            {
+                "title": "截止日期",
+                "start_time": "2026-07-05T23:59:00+00:00",
+                "end_time": "2026-07-05T23:59:00+00:00",
+                "description": "提交报告",
+            },
+        ]
+    )
+    gateway = MockLLMGateway(response=llm_response)
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="本周有几个安排和截止",
+        conversation_id="conv-multi",
+        user_id="user-1",
+    )
+
+    assert len(result) == 3
+    titles = {e["title"] for e in result}
+    assert titles == {"会议A", "会议B", "截止日期"}
+    for event in result:
+        assert event["source"] == "post_extract"
+        assert event["conversation_id"] == "conv-multi"
+
+
+# ---------------------------------------------------------------------------
+# Items without 'title' key are filtered out
+# ---------------------------------------------------------------------------
+
+
+async def test_items_without_title_filtered(
+    extractor: PostProcessingExtractor,
+) -> None:
+    """Dict items missing 'title' are dropped by the parser."""
+    llm_response = json.dumps(
+        [
+            {
+                "title": "有效会议",
+                "start_time": "2026-07-01T09:00:00+00:00",
+                "end_time": "2026-07-01T10:00:00+00:00",
+                "description": "",
+            },
+            {"start_time": "2026-07-02T09:00:00+00:00", "end_time": "2026-07-02T10:00:00+00:00"},
+            "not-a-dict",
+        ]
+    )
+    gateway = MockLLMGateway(response=llm_response)
+    extractor.llm_gateway = gateway
+
+    result = await extractor.extract(
+        conversation_text="明天开会",
+        conversation_id="conv-1",
+        user_id="user-1",
+    )
+
+    assert len(result) == 1
+    assert result[0]["title"] == "有效会议"