diff --git a/.coverage b/.coverage
deleted file mode 100644
index dab01fc..0000000
Binary files a/.coverage and /dev/null differ
diff --git a/chat.py b/chat.py
index bb37377..42346a2 100644
--- a/chat.py
+++ b/chat.py
@@ -3,6 +3,7 @@
 
 import asyncio
 
+from google import genai
 from google.adk.agents import LlmAgent
 from google.adk.runners import Runner
 from google.cloud.firestore_v1.async_client import AsyncClient
@@ -22,7 +23,11 @@ root_agent = LlmAgent(
 
 async def main() -> None:
     db = AsyncClient()
-    session_service = FirestoreSessionService(db=db)
+    session_service = FirestoreSessionService(
+        db=db,
+        compaction_token_threshold=800_000,
+        genai_client=genai.Client(),
+    )
 
     runner = Runner(
         app_name=APP_NAME,
@@ -30,11 +35,25 @@ async def main() -> None:
         session_service=session_service,
     )
 
-    session = await session_service.create_session(
-        app_name=APP_NAME,
-        user_id=USER_ID,
+    # Reuse existing session or create a new one
+    resp = await session_service.list_sessions(
+        app_name=APP_NAME, user_id=USER_ID
     )
-    print(f"Session {session.id} created. Type 'exit' to quit.\n")
+    if resp.sessions:
+        session = await session_service.get_session(
+            app_name=APP_NAME,
+            user_id=USER_ID,
+            session_id=resp.sessions[0].id,
+        )
+        print(f"Resuming session {session.id}.")
+    else:
+        session = await session_service.create_session(
+            app_name=APP_NAME,
+            user_id=USER_ID,
+        )
+        print(f"Session {session.id} created.")
+
+    print("Type 'exit' to quit.\n")
 
     while True:
         try:
diff --git a/src/adk_firestore_sessionmanager/firestore_session_service.py b/src/adk_firestore_sessionmanager/firestore_session_service.py
index f1fa67c..c0c4071 100644
--- a/src/adk_firestore_sessionmanager/firestore_session_service.py
+++ b/src/adk_firestore_sessionmanager/firestore_session_service.py
@@ -7,6 +7,7 @@ import time
 from typing import Any, Optional
 import uuid
 
+from google import genai
 from google.adk.errors.already_exists_error import AlreadyExistsError
 from google.adk.events.event import Event
 from google.adk.sessions import _session_util
@@ -19,6 +20,7 @@ from google.adk.sessions.session import Session
 from google.adk.sessions.state import State
 from google.cloud.firestore_v1.async_client import AsyncClient
 from google.cloud.firestore_v1.field_path import FieldPath
+from google.genai.types import Content, Part
 from typing_extensions import override
 
 logger = logging.getLogger("google_adk." + __name__)
@@ -45,9 +47,21 @@ class FirestoreSessionService(BaseSessionService):
         *,
         db: AsyncClient,
         collection_prefix: str = "adk",
+        compaction_token_threshold: int | None = None,
+        compaction_model: str = "gemini-2.5-flash",
+        compaction_keep_recent: int = 10,
+        genai_client: genai.Client | None = None,
     ) -> None:
+        if compaction_token_threshold is not None and genai_client is None:
+            raise ValueError(
+                "genai_client is required when compaction_token_threshold is set."
+            )
         self._db = db
         self._prefix = collection_prefix
+        self._compaction_threshold = compaction_token_threshold
+        self._compaction_model = compaction_model
+        self._compaction_keep_recent = compaction_keep_recent
+        self._genai_client = genai_client
 
     # ------------------------------------------------------------------
     # Document-reference helpers
@@ -100,6 +114,100 @@ class FirestoreSessionService(BaseSessionService):
             merged[State.USER_PREFIX + key] = value
         return merged
 
+    # ------------------------------------------------------------------
+    # Compaction helpers
+    # ------------------------------------------------------------------
+
+    @staticmethod
+    def _events_to_text(events: list[Event]) -> str:
+        lines: list[str] = []
+        for event in events:
+            if event.content and event.content.parts:
+                text = "".join(p.text or "" for p in event.content.parts)
+                if text:
+                    role = "User" if event.author == "user" else "Assistant"
+                    lines.append(f"{role}: {text}")
+        return "\n\n".join(lines)
+
+    async def _generate_summary(
+        self, existing_summary: str, events: list[Event]
+    ) -> str:
+        conversation_text = self._events_to_text(events)
+        previous = (
+            "Previous summary of earlier conversation:\n"
+            f"{existing_summary}\n\n"
+            if existing_summary
+            else ""
+        )
+        prompt = (
+            "Summarize the following conversation between a user and an "
+            "assistant. Preserve:\n"
+            "- Key decisions and conclusions\n"
+            "- User preferences and requirements\n"
+            "- Important facts, names, and numbers\n"
+            "- The overall topic and direction of the conversation\n"
+            "- Any pending tasks or open questions\n\n"
+            f"{previous}"
+            f"Conversation:\n{conversation_text}\n\n"
+            "Provide a clear, comprehensive summary."
+        )
+        assert self._genai_client is not None
+        response = await self._genai_client.aio.models.generate_content(
+            model=self._compaction_model,
+            contents=prompt,
+        )
+        return response.text or ""
+
+    async def _compact_session(self, session: Session) -> None:
+        app_name = session.app_name
+        user_id = session.user_id
+        session_id = session.id
+
+        events_ref = self._events_col(app_name, user_id, session_id)
+        query = events_ref.order_by("timestamp")
+        event_docs = await query.get()
+
+        if len(event_docs) <= self._compaction_keep_recent:
+            return
+
+        all_events = [
+            Event.model_validate(doc.to_dict()) for doc in event_docs
+        ]
+        events_to_summarize = all_events[: -self._compaction_keep_recent]
+
+        session_snap = await self._session_ref(
+            app_name, user_id, session_id
+        ).get()
+        existing_summary = (session_snap.to_dict() or {}).get(
+            "conversation_summary", ""
+        )
+
+        try:
+            summary = await self._generate_summary(
+                existing_summary, events_to_summarize
+            )
+        except Exception:
+            logger.exception("Compaction summary generation failed; skipping.")
+            return
+
+        docs_to_delete = event_docs[: -self._compaction_keep_recent]
+        for i in range(0, len(docs_to_delete), 500):
+            batch = self._db.batch()
+            for doc in docs_to_delete[i : i + 500]:
+                batch.delete(doc.reference)
+            await batch.commit()
+
+        await self._session_ref(app_name, user_id, session_id).update(
+            {"conversation_summary": summary}
+        )
+
+        logger.info(
+            "Compacted session %s: summarised %d events, kept %d.",
+            session_id,
+            len(docs_to_delete),
+            self._compaction_keep_recent,
+        )
+
     # ------------------------------------------------------------------
     # BaseSessionService implementation
     # ------------------------------------------------------------------
@@ -190,6 +298,47 @@ class FirestoreSessionService(BaseSessionService):
         if config and config.num_recent_events:
             events = events[-config.num_recent_events :]
 
+        # Prepend conversation summary as synthetic context events
+        conversation_summary = session_data.get("conversation_summary")
+        if conversation_summary:
+            summary_event = Event(
+                id="summary-context",
+                author="user",
+                content=Content(
+                    role="user",
+                    parts=[
+                        Part(
+                            text=(
+                                "[Conversation context from previous"
+                                " messages]\n"
+                                f"{conversation_summary}"
+                            )
+                        )
+                    ],
+                ),
+                timestamp=0.0,
+                invocation_id="compaction-summary",
+            )
+            ack_event = Event(
+                id="summary-ack",
+                author=app_name,
+                content=Content(
+                    role="model",
+                    parts=[
+                        Part(
+                            text=(
+                                "Understood, I have the context from our"
+                                " previous conversation and will continue"
+                                " accordingly."
+                            )
+                        )
+                    ],
+                ),
+                timestamp=0.001,
+                invocation_id="compaction-summary",
+            )
+            events = [summary_event, ack_event] + events
+
         # Merge scoped state
         app_state = await self._get_app_state(app_name)
         user_state = await self._get_user_state(app_name, user_id)
@@ -313,4 +462,14 @@ class FirestoreSessionService(BaseSessionService):
         else:
             await session_ref.update({"last_update_time": event.timestamp})
 
+        # Trigger compaction if total token count exceeds threshold
+        if (
+            self._compaction_threshold is not None
+            and event.usage_metadata
+            and event.usage_metadata.total_token_count
+            and event.usage_metadata.total_token_count
+            >= self._compaction_threshold
+        ):
+            await self._compact_session(session)
+
         return event
diff --git a/tests/conftest.py b/tests/conftest.py
index 1ca3382..93e9424 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -11,7 +11,7 @@ from google.cloud.firestore_v1.async_client import AsyncClient
 
 from adk_firestore_sessionmanager import FirestoreSessionService
 
-os.environ.setdefault("FIRESTORE_EMULATOR_HOST", "localhost:8161")
+os.environ.setdefault("FIRESTORE_EMULATOR_HOST", "localhost:8219")
 
 
 @pytest_asyncio.fixture
diff --git a/tests/test_compaction.py b/tests/test_compaction.py
new file mode 100644
index 0000000..788f937
--- /dev/null
+++ b/tests/test_compaction.py
@@ -0,0 +1,282 @@
+"""Tests for conversation compaction in FirestoreSessionService."""
+
+from __future__ import annotations
+
+import time
+from unittest.mock import AsyncMock, MagicMock
+import uuid
+
+import pytest
+import pytest_asyncio
+from google import genai
+from google.adk.events.event import Event
+from google.cloud.firestore_v1.async_client import AsyncClient
+from google.genai.types import Content, GenerateContentResponseUsageMetadata, Part
+
+from adk_firestore_sessionmanager import FirestoreSessionService
+
+pytestmark = pytest.mark.asyncio
+
+
+@pytest_asyncio.fixture
+async def mock_genai_client():
+    client = MagicMock(spec=genai.Client)
+    response = MagicMock()
+    response.text = "Summary of the conversation so far."
+    client.aio.models.generate_content = AsyncMock(return_value=response)
+    return client
+
+
+@pytest_asyncio.fixture
+async def compaction_service(db: AsyncClient, mock_genai_client):
+    prefix = f"test_{uuid.uuid4().hex[:8]}"
+    return FirestoreSessionService(
+        db=db,
+        collection_prefix=prefix,
+        compaction_token_threshold=100,
+        compaction_keep_recent=2,
+        genai_client=mock_genai_client,
+    )
+
+
+# ------------------------------------------------------------------
+# __init__ validation
+# ------------------------------------------------------------------
+
+
+class TestCompactionInit:
+    async def test_requires_genai_client(self, db):
+        with pytest.raises(ValueError, match="genai_client is required"):
+            FirestoreSessionService(
+                db=db,
+                compaction_token_threshold=1000,
+            )
+
+    async def test_no_threshold_no_client_ok(self, db):
+        svc = FirestoreSessionService(db=db)
+        assert svc._compaction_threshold is None
+
+
+# ------------------------------------------------------------------
+# Compaction trigger
+# ------------------------------------------------------------------
+
+
+class TestCompactionTrigger:
+    async def test_compaction_triggered_above_threshold(
+        self, compaction_service, mock_genai_client, app_name, user_id
+    ):
+        session = await compaction_service.create_session(
+            app_name=app_name, user_id=user_id
+        )
+
+        # Add 5 events, last one with usage_metadata above threshold
+        base = time.time()
+        for i in range(4):
+            e = Event(
+                author="user" if i % 2 == 0 else app_name,
+                content=Content(
+                    role="user" if i % 2 == 0 else "model",
+                    parts=[Part(text=f"message {i}")],
+                ),
+                timestamp=base + i,
+                invocation_id=f"inv-{i}",
+            )
+            await compaction_service.append_event(session, e)
+
+        # This event crosses the threshold
+        trigger_event = Event(
+            author=app_name,
+            content=Content(
+                role="model", parts=[Part(text="final response")]
+            ),
+            timestamp=base + 4,
+            invocation_id="inv-4",
+            usage_metadata=GenerateContentResponseUsageMetadata(
+                total_token_count=200,
+            ),
+        )
+        await compaction_service.append_event(session, trigger_event)
+
+        # Summary generation should have been called
+        mock_genai_client.aio.models.generate_content.assert_called_once()
+
+        # Fetch session: should have summary + only keep_recent events
+        fetched = await compaction_service.get_session(
+            app_name=app_name, user_id=user_id, session_id=session.id
+        )
+        # 2 synthetic summary events + 2 kept real events
+        assert len(fetched.events) == 4
+        assert fetched.events[0].id == "summary-context"
+        assert fetched.events[1].id == "summary-ack"
+        assert "Summary of the conversation" in fetched.events[0].content.parts[0].text
+
+    async def test_no_compaction_below_threshold(
+        self, compaction_service, mock_genai_client, app_name, user_id
+    ):
+        session = await compaction_service.create_session(
+            app_name=app_name, user_id=user_id
+        )
+        event = Event(
+            author=app_name,
+            content=Content(
+                role="model", parts=[Part(text="short reply")]
+            ),
+            timestamp=time.time(),
+            invocation_id="inv-1",
+            usage_metadata=GenerateContentResponseUsageMetadata(
+                total_token_count=50,
+            ),
+        )
+        await compaction_service.append_event(session, event)
+
+        mock_genai_client.aio.models.generate_content.assert_not_called()
+
+    async def test_no_compaction_without_usage_metadata(
+        self, compaction_service, mock_genai_client, app_name, user_id
+    ):
+        session = await compaction_service.create_session(
+            app_name=app_name, user_id=user_id
+        )
+        event = Event(
+            author="user",
+            content=Content(
+                role="user", parts=[Part(text="hello")]
+            ),
+            timestamp=time.time(),
+            invocation_id="inv-1",
+        )
+        await compaction_service.append_event(session, event)
+
+        mock_genai_client.aio.models.generate_content.assert_not_called()
+
+
+# ------------------------------------------------------------------
+# Compaction with too few events (nothing to compact)
+# ------------------------------------------------------------------
+
+
+class TestCompactionEdgeCases:
+    async def test_skip_when_fewer_events_than_keep_recent(
+        self, compaction_service, mock_genai_client, app_name, user_id
+    ):
+        session = await compaction_service.create_session(
+            app_name=app_name, user_id=user_id
+        )
+        # Only 2 events, keep_recent=2 → nothing to summarize
+        for i in range(2):
+            e = Event(
+                author="user",
+                content=Content(
+                    role="user", parts=[Part(text=f"msg {i}")]
+                ),
+                timestamp=time.time() + i,
+                invocation_id=f"inv-{i}",
+            )
+            await compaction_service.append_event(session, e)
+
+        # Trigger compaction manually even though threshold wouldn't fire
+        await compaction_service._compact_session(session)
+
+        mock_genai_client.aio.models.generate_content.assert_not_called()
+
+    async def test_summary_generation_failure_is_non_fatal(
+        self, compaction_service, mock_genai_client, app_name, user_id
+    ):
+        session = await compaction_service.create_session(
+            app_name=app_name, user_id=user_id
+        )
+        for i in range(5):
+            e = Event(
+                author="user",
+                content=Content(
+                    role="user", parts=[Part(text=f"msg {i}")]
+                ),
+                timestamp=time.time() + i,
+                invocation_id=f"inv-{i}",
+            )
+            await compaction_service.append_event(session, e)
+
+        # Make summary generation fail
+        mock_genai_client.aio.models.generate_content = AsyncMock(
+            side_effect=RuntimeError("API error")
+        )
+
+        # Should not raise
+        await compaction_service._compact_session(session)
+
+        # All events should still be present
+        fetched = await compaction_service.get_session(
+            app_name=app_name, user_id=user_id, session_id=session.id
+        )
+        assert len(fetched.events) == 5
+
+
+# ------------------------------------------------------------------
+# get_session with summary
+# ------------------------------------------------------------------
+
+
+class TestGetSessionWithSummary:
+    async def test_no_summary_no_synthetic_events(
+        self, compaction_service, app_name, user_id
+    ):
+        session = await compaction_service.create_session(
+            app_name=app_name, user_id=user_id
+        )
+        event = Event(
+            author="user",
+            content=Content(
+                role="user", parts=[Part(text="hello")]
+            ),
+            timestamp=time.time(),
+            invocation_id="inv-1",
+        )
+        await compaction_service.append_event(session, event)
+
+        fetched = await compaction_service.get_session(
+            app_name=app_name, user_id=user_id, session_id=session.id
+        )
+        assert len(fetched.events) == 1
+        assert fetched.events[0].author == "user"
+
+
+# ------------------------------------------------------------------
+# _events_to_text
+# ------------------------------------------------------------------
+
+
+class TestEventsToText:
+    def test_formats_user_and_assistant(self):
+        events = [
+            Event(
+                author="user",
+                content=Content(
+                    role="user", parts=[Part(text="Hi there")]
+                ),
+                timestamp=1.0,
+                invocation_id="inv-1",
+            ),
+            Event(
+                author="bot",
+                content=Content(
+                    role="model", parts=[Part(text="Hello!")]
+                ),
+                timestamp=2.0,
+                invocation_id="inv-2",
+            ),
+        ]
+        text = FirestoreSessionService._events_to_text(events)
+        assert "User: Hi there" in text
+        assert "Assistant: Hello!" in text
+
+    def test_skips_events_without_text(self):
+        events = [
+            Event(
+                author="user",
+                timestamp=1.0,
+                invocation_id="inv-1",
+            ),
+        ]
+        text = FirestoreSessionService._events_to_text(events)
+        assert text == ""
diff --git a/view_summary.py b/view_summary.py
new file mode 100644
index 0000000..e60c73e
--- /dev/null
+++ b/view_summary.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+"""Print the conversation summary for a specific user's session."""
+
+import asyncio
+
+from google.cloud.firestore_v1.async_client import AsyncClient
+
+from adk_firestore_sessionmanager import FirestoreSessionService
+
+APP_NAME = "test_agent"
+USER_ID = "dev_user"
+
+
+async def main() -> None:
+    db = AsyncClient()
+    session_service = FirestoreSessionService(db=db)
+
+    resp = await session_service.list_sessions(
+        app_name=APP_NAME, user_id=USER_ID
+    )
+
+    if not resp.sessions:
+        print("No sessions found.")
+        return
+
+    for s in resp.sessions:
+        ref = session_service._session_ref(APP_NAME, USER_ID, s.id)
+        snap = await ref.get()
+        data = snap.to_dict() or {}
+        summary = data.get("conversation_summary")
+
+        print(f"Session: {s.id}")
+        if summary:
+            print(f"Summary:\n{summary}")
+        else:
+            print("No summary yet.")
+        print()
+
+
+if __name__ == "__main__":
+    asyncio.run(main())