diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index c68e7b5..8a208f3 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -20,30 +20,34 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: [ '3.8', '3.9', '3.10', '3.11', '3.12' ]
+        python-version: [ '3.9', '3.10', '3.11', '3.12', '3.13' ]
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
-    - uses: actions/setup-python@v4
+    - uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
 
     - name: Upgrade pip
       run: python3 -m pip install --upgrade pip
 
+    - name: Ensure pip >= v25.1
+      run: python -m pip install "pip >= 25.1"
+
     - name: Install ypywidgets in dev mode
-      run: pip install -e ".[dev]"
+      run: pip install --group dev -e .
 
     - name: Check types
       run: mypy src
 
     - name: Run tests
+      if: ${{ !((matrix.python-version == '3.13') && (matrix.os == 'ubuntu-latest')) }}
       run: pytest ./tests -v --color=yes
 
     - name: Run code coverage
-      if: ${{ (matrix.python-version == '3.12') && (matrix.os == 'ubuntu-latest') }}
+      if: ${{ (matrix.python-version == '3.13') && (matrix.os == 'ubuntu-latest') }}
       run: |
         coverage run -m pytest tests
         coverage report --fail-under=100
diff --git a/pyproject.toml b/pyproject.toml
index 428c59e..562192d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,7 +8,7 @@ version = "0.9.7"
 description = "Y-based Jupyter widgets for Python"
 readme = "README.md"
 license = "MIT"
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 authors = [
     { name = "David Brochart", email = "david.brochart@gmail.com" },
 ]
@@ -24,9 +24,9 @@ dependencies = [
 ]
 
 [project.urls]
-Homepage = "https://github.com/davidbrochart/ypywidgets"
+Homepage = "https://github.com/QuantStack/ypywidgets"
 
-[project.optional-dependencies]
+[dependency-groups]
 dev = [
     "coverage >=7.0.0,<8.0.0",
     "mypy",
diff --git a/src/ypywidgets/comm.py b/src/ypywidgets/comm.py
index 89a5a89..757ae8f 100644
--- a/src/ypywidgets/comm.py
+++ b/src/ypywidgets/comm.py
@@ -1,5 +1,8 @@
 from __future__ import annotations
 
+from collections.abc import Callable
+from typing import Any
+
 import comm
 from pycrdt import (
     Doc,
@@ -41,6 +44,8 @@ def create_widget_comm(
 
 
 class CommProvider:
+    _on_receive: Callable[[bytes], None] | None
+
     def __init__(
         self,
         ydoc: Doc,
@@ -48,33 +53,45 @@ def __init__(
     ) -> None:
         self._ydoc = ydoc
         self._comm = comm
+        self._on_receive = None
         msg = create_sync_message(ydoc)
         self._comm.send(buffers=[msg])
         self._comm.on_msg(self._receive)
 
-    def _receive(self, msg):
+    def _receive(self, msg: dict[str, Any]):
         message = bytes(msg["buffers"][0])
-        if message[0] == YMessageType.SYNC:
-            reply = handle_sync_message(message[1:], self._ydoc)
+        message_type = message[0]
+        message_content = message[1:]
+        if message_type == YMessageType.SYNC:
+            reply = handle_sync_message(message_content, self._ydoc)
             if reply is not None:
                 self._comm.send(buffers=[reply])
             if message[1] == YSyncMessageType.SYNC_STEP2:
                 self._ydoc.observe(self._send)
+        elif message_type == 2:
+            if self._on_receive is not None:
+                self._on_receive(message_content)
 
     def _send(self, event: TransactionEvent):
         update = event.update
         message = create_update_message(update)
         self._comm.send(buffers=[message])
 
+    def on_receive(self, callback: Callable[[bytes], None]):
+        self._on_receive = callback
+
+    def send(self, message: bytes):
+        self._comm.send(buffers=[bytes([2]) + message])
+
 
 class CommWidget(Widget):
     def __init__(
-            self,
-            ydoc: Doc | None = None,
-            comm_data: dict | None = None,
-            comm_metadata: dict | None = None,
-            comm_id: str | None = None,
-        ):
+        self,
+        ydoc: Doc | None = None,
+        comm_data: dict | None = None,
+        comm_metadata: dict | None = None,
+        comm_id: str | None = None,
+    ):
         super().__init__(ydoc)
         model_name = self.__class__.__name__
         _model_name = self.ydoc["_model_name"] = Text()
@@ -85,7 +102,7 @@ def __init__(
                 create_ydoc=not ydoc,
             )
         self._comm = create_widget_comm(comm_data, comm_metadata, comm_id)
-        CommProvider(self.ydoc, self._comm)
+        self._provider = CommProvider(self.ydoc, self._comm)
 
     def _repr_mimebundle_(self, *args, **kwargs):  # pragma: nocover
         plaintext = repr(self)
@@ -100,3 +117,9 @@ def _repr_mimebundle_(self, *args, **kwargs):  # pragma: nocover
             }
         }
         return data
+
+    def on_receive(self, callback: Callable[[bytes], None]) -> None:
+        self._provider.on_receive(callback)
+
+    def send(self, message: bytes) -> None:
+        self._provider.send(message)
diff --git a/tests/conftest.py b/tests/conftest.py
index b7a0ea5..df54a65 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,18 +1,12 @@
+from __future__ import annotations
+
 import asyncio
 import time
-from typing import Optional
 
 import comm
 import pytest
-from pycrdt import (
-    YMessageType,
-    YSyncMessageType,
-    TransactionEvent,
-    create_sync_message,
-    create_update_message,
-    handle_sync_message,
-)
-from ypywidgets import Widget
+import pytest_asyncio
+from pycrdt import create_sync_message
 from ypywidgets.comm import CommWidget
 
 
@@ -47,10 +41,10 @@ async def receive(self):
 
 @pytest.fixture
 def widget_factories():
-    return CommWidget, Widget
+    return CommWidget, CommWidget
 
 
-@pytest.fixture
+@pytest_asyncio.fixture
 async def synced_widgets(widget_factories):
     local_widget = widget_factories[0]()
     remote_widget_manager = RemoteWidgetManager(widget_factories[1], local_widget._comm)
@@ -60,35 +54,31 @@ async def synced_widgets(widget_factories):
 
 class RemoteWidgetManager:
 
-    comm: Optional[MockComm]
-    widget: Optional[Widget]
+    comm: MockComm
+    widget: CommWidget | None
 
-    def __init__(self, widget_factory, comm):
+    def __init__(self, widget_factory, local_comm):
         self.widget_factory = widget_factory
-        self.comm = comm
+        self.local_comm = local_comm
         self.widget = None
         self.receive_task = asyncio.create_task(self.receive())
 
-    def send(self, event: TransactionEvent):
-        update = event.update
-        message = create_update_message(update)
-        self.comm.recv_queue.put_nowait({"buffers": [message]})
+    async def send(self):
+        while True:
+            msg_type, data, metadata, buffers, target_name, target_module = await self.widget._comm.send_queue.get()
+            if msg_type == "comm_msg":
+                self.local_comm.recv_queue.put_nowait({"buffers": buffers})
 
     async def receive(self):
         while True:
-            msg_type, data, metadata, buffers, target_name, target_module = await self.comm.send_queue.get()
+            msg_type, data, metadata, buffers, target_name, target_module = await self.local_comm.send_queue.get()
             if msg_type == "comm_open":
                 self.widget = self.widget_factory()
                 msg = create_sync_message(self.widget.ydoc)
-                self.comm.handle_msg({"buffers": [msg]})
+                self.local_comm.recv_queue.put_nowait({"buffers": [msg]})
+                self.send_task = asyncio.create_task(self.send())
             elif msg_type == "comm_msg":
-                message = buffers[0]
-                if message[0] == YMessageType.SYNC:
-                    reply = handle_sync_message(message[1:], self.widget.ydoc)
-                    if reply is not None:
-                        self.comm.handle_msg({"buffers": [reply]})
-                    if message[1] == YSyncMessageType.SYNC_STEP2:
-                        self.widget.ydoc.observe(self.send)
+                self.widget._comm.recv_queue.put_nowait({"buffers": buffers})
 
     async def get_widget(self, timeout=0.1):
         t = time.monotonic()
diff --git a/tests/test_attributes.py b/tests/test_attributes.py
index 4bcfe85..e20ca5c 100644
--- a/tests/test_attributes.py
+++ b/tests/test_attributes.py
@@ -23,7 +23,7 @@ def _watch_foo(self, old, new):
 
 @pytest.mark.asyncio
 async def test_create_ydoc(synced_widgets):
-    local_widget, remote_widget = await synced_widgets
+    local_widget, remote_widget = synced_widgets
 
     local_text = Text()
     local_widget.ydoc["text"] = local_text
@@ -39,7 +39,7 @@ async def test_create_ydoc(synced_widgets):
 @pytest.mark.asyncio
 @pytest.mark.parametrize("widget_factories", ((Widget1, Widget1),))
 async def test_sync_attribute(widget_factories, synced_widgets):
-    local_widget, remote_widget = await synced_widgets
+    local_widget, remote_widget = synced_widgets
 
     with pytest.raises(AttributeError):
         assert local_widget.wrong_attr1
@@ -61,7 +61,7 @@ async def test_sync_attribute(widget_factories, synced_widgets):
 @pytest.mark.asyncio
 @pytest.mark.parametrize("widget_factories", ((Widget1, Widget2),))
 async def test_watch_attribute(widget_factories, synced_widgets, capfd):
-    local_widget, remote_widget = await synced_widgets
+    local_widget, remote_widget = synced_widgets
 
     local_widget.foo = "foo"
 
diff --git a/tests/test_messages.py b/tests/test_messages.py
new file mode 100644
index 0000000..9c2ebdf
--- /dev/null
+++ b/tests/test_messages.py
@@ -0,0 +1,30 @@
+import asyncio
+
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_messages(synced_widgets):
+    local_messages = []
+    remote_messages = []
+    local_widget, remote_widget = synced_widgets
+
+    def on_local_message(message):
+        local_messages.append(message)
+
+    def on_remote_message(message):
+        remote_messages.append(message)
+        remote_widget.send(message + b", World!")
+
+    local_widget.on_receive(on_local_message)
+    remote_widget.on_receive(on_remote_message)
+
+    local_widget.send(b"Hello")
+    await asyncio.sleep(0.1)
+    assert remote_messages == [b"Hello"]
+    assert local_messages == [b"Hello, World!"]
+
+    remote_widget.send(b"msg")
+    await asyncio.sleep(0.1)
+    assert remote_messages == [b"Hello"]
+    assert local_messages == [b"Hello, World!", b"msg"]