diff --git a/pocketstation/__init__.py b/pocketstation/__init__.py
index 3dc1f76..a43259a 100644
--- a/pocketstation/__init__.py
+++ b/pocketstation/__init__.py
@@ -1 +1,12 @@
+"""PocketStation Python SDK. Phase 5."""
+from .client import PocketStation, PocketStationSession
+from .types import IceServer, PocketStationError, RoomCredentials
+
 __version__ = "0.1.0"
+__all__ = [
+    "PocketStation",
+    "PocketStationSession",
+    "RoomCredentials",
+    "IceServer",
+    "PocketStationError",
+]
diff --git a/pocketstation/client.py b/pocketstation/client.py
new file mode 100644
index 0000000..3fc3238
--- /dev/null
+++ b/pocketstation/client.py
@@ -0,0 +1,137 @@
+"""
+PocketStation Python async client SDK.
+
+Phase scope: Phase 5.
+
+Usage::
+
+    import asyncio
+    from pocketstation import PocketStation
+
+    async def main():
+        async with PocketStation.connect(
+            api_url="https://api.pocketstation.io",
+            relay_url="wss://relay.pocketstation.io",
+        ) as session:
+            print(f"Connected to room {session.room_id}")
+            creds = session.credentials
+            # Use creds.source_token / creds.listener_token for signaling
+
+    asyncio.run(main())
+"""
+from __future__ import annotations
+
+import json
+from contextlib import asynccontextmanager
+from typing import AsyncGenerator, Optional
+
+import httpx
+
+from .types import IceServer, PocketStationError, RoomCredentials
+
+
+class PocketStationSession:
+    """
+    Active PocketStation session.
+
+    Invariant: valid only within the ``async with PocketStation.connect()`` block.
+    Ownership: created and owned by PocketStation.connect(); do not instantiate directly.
+    Failure behavior: network errors raise PocketStationError.
+
+    Phase 5: HTTP room creation implemented. WebSocket signaling and WebRTC
+    publish/subscribe wiring are Phase 5 follow-up (requires native WebRTC
+    Python binding or aiortc).
+    """
+
+    def __init__(self, credentials: RoomCredentials) -> None:
+        self._credentials = credentials
+
+    @property
+    def credentials(self) -> RoomCredentials:
+        """Room credentials including TURN servers (ADR-023)."""
+        return self._credentials
+
+    @property
+    def room_id(self) -> str:
+        return self._credentials.room_id
+
+    @property
+    def source_token(self) -> str:
+        return self._credentials.source_token
+
+    @property
+    def listener_token(self) -> str:
+        return self._credentials.listener_token
+
+    @property
+    def ice_servers(self) -> list[IceServer]:
+        """TURN/STUN servers for WebRTC PeerConnection config."""
+        return self._credentials.ice_servers
+
+
+class PocketStation:
+    """
+    PocketStation async context manager.
+
+    Creates a room on enter, cleans up on exit.
+    """
+
+    @staticmethod
+    @asynccontextmanager
+    async def connect(
+        *,
+        api_url: str,
+        relay_url: str,
+        credentials: Optional[RoomCredentials] = None,
+    ) -> AsyncGenerator[PocketStationSession, None]:
+        """
+        Async context manager that creates a PocketStation session.
+
+        On entry: creates a new room via POST /v1/rooms (or uses provided credentials).
+        On exit: releases the session (future: sends LEAVE, closes WebSocket).
+
+        :param api_url: Base URL of the api-server.
+        :param relay_url: Base URL of the relay (wss://...).
+        :param credentials: Pre-obtained credentials. If None, a new room is created.
+        :raises PocketStationError: on network or protocol failure.
+        """
+        if credentials is None:
+            credentials = await PocketStation._create_room(api_url)
+
+        session = PocketStationSession(credentials)
+        try:
+            yield session
+        finally:
+            # Phase 5 TODO: send LEAVE via signaling WebSocket.
+            pass
+
+    @staticmethod
+    async def create_room(api_url: str) -> RoomCredentials:
+        """Create a new room and return credentials. Does not start a session."""
+        return await PocketStation._create_room(api_url)
+
+    @staticmethod
+    async def _create_room(api_url: str) -> RoomCredentials:
+        url = api_url.rstrip("/") + "/v1/rooms"
+        try:
+            async with httpx.AsyncClient() as http:
+                response = await http.post(url, json={})
+        except httpx.RequestError as exc:
+            raise PocketStationError(
+                f"network error creating room: {exc}", "network_error"
+            ) from exc
+
+        if not response.is_success:
+            raise PocketStationError(
+                f"relay returned HTTP {response.status_code}: {response.text}",
+                "http_error",
+            )
+
+        try:
+            data = response.json()
+        except json.JSONDecodeError as exc:
+            raise PocketStationError(
+                f"failed to parse room creation response: {exc}", "parse_error"
+            ) from exc
+
+        return RoomCredentials.from_dict(data)
diff --git a/pocketstation/types.py b/pocketstation/types.py
new file mode 100644
index 0000000..17d5549
--- /dev/null
+++ b/pocketstation/types.py
@@ -0,0 +1,45 @@
+"""PocketStation SDK type definitions. Phase 5."""
+from __future__ import annotations
+from dataclasses import dataclass, field
+from typing import Optional
+
+
+@dataclass
+class IceServer:
+    """ICE server configuration (ADR-023 embedded TURN)."""
+    urls: list[str]
+    username: Optional[str] = None
+    credential: Optional[str] = None
+
+
+@dataclass
+class RoomCredentials:
+    """Credentials returned by POST /v1/rooms."""
+    room_id: str
+    source_token: str
+    listener_token: str
+    ice_servers: list[IceServer] = field(default_factory=list)
+
+    @classmethod
+    def from_dict(cls, data: dict) -> "RoomCredentials":
+        ice_servers = [
+            IceServer(
+                urls=srv.get("urls", []),
+                username=srv.get("username"),
+                credential=srv.get("credential"),
+            )
+            for srv in data.get("ice_servers", [])
+        ]
+        return cls(
+            room_id=data["room_id"],
+            source_token=data["source_token"],
+            listener_token=data["listener_token"],
+            ice_servers=ice_servers,
+        )
+
+
+class PocketStationError(Exception):
+    """Base error for all PocketStation SDK failures."""
+    def __init__(self, message: str, code: str = "error") -> None:
+        super().__init__(message)
+        self.code = code
diff --git a/pyproject.toml b/pyproject.toml
index 20f68e4..70500f9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,3 +1,20 @@
 [project]
-name="pocketstation"
-version="0.1.0"
+name = "pocketstation"
+version = "0.1.0"
+description = "PocketStation Python client SDK"
+requires-python = ">=3.11"
+license = { text = "MIT" }
+dependencies = [
+    "httpx>=0.27",
+    "websockets>=12.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0",
+    "pytest-asyncio>=0.23",
+    "respx>=0.21",
+]
+
+[tool.pytest.ini_options]
+asyncio_mode = "auto"
diff --git a/tests/test_client.py b/tests/test_client.py
new file mode 100644
index 0000000..3bf2de9
--- /dev/null
+++ b/tests/test_client.py
@@ -0,0 +1,98 @@
+"""Unit tests for pocketstation.client. Phase 5."""
+import pytest
+import httpx
+import respx
+
+from pocketstation import PocketStation, PocketStationError, RoomCredentials
+
+
+VALID_ROOM_RESPONSE = {
+    "room_id": "room-py-001",
+    "source_token": "src-py",
+    "listener_token": "lst-py",
+}
+
+
+@respx.mock
+@pytest.mark.asyncio
+async def test_given_valid_api_server_when_connect_then_session_has_credentials():
+    # Given
+    respx.post("http://api.example.com/v1/rooms").mock(
+        return_value=httpx.Response(201, json=VALID_ROOM_RESPONSE)
+    )
+    # When
+    async with PocketStation.connect(
+        api_url="http://api.example.com",
+        relay_url="ws://relay.example.com",
+    ) as session:
+        # Then
+        assert session.room_id == "room-py-001"
+        assert session.source_token == "src-py"
+        assert session.listener_token == "lst-py"
+        assert session.ice_servers == []
+
+
+@respx.mock
+@pytest.mark.asyncio
+async def test_given_api_server_with_turn_when_connect_then_ice_servers_forwarded():
+    # Given
+    respx.post("http://api.example.com/v1/rooms").mock(
+        return_value=httpx.Response(201, json={
+            **VALID_ROOM_RESPONSE,
+            "ice_servers": [
+                {"urls": ["stun:relay.example.com:3478"]},
+                {"urls": ["turn:relay.example.com:3478"], "username": "u", "credential": "p"},
+            ],
+        })
+    )
+    # When
+    async with PocketStation.connect(
+        api_url="http://api.example.com",
+        relay_url="ws://relay.example.com",
+    ) as session:
+        # Then
+        assert len(session.ice_servers) == 2
+        assert session.ice_servers[1].username == "u"
+
+
+@respx.mock
+@pytest.mark.asyncio
+async def test_given_api_server_500_when_connect_then_raises():
+    # Given
+    respx.post("http://api.example.com/v1/rooms").mock(
+        return_value=httpx.Response(500, text="internal error")
+    )
+    # When / Then
+    with pytest.raises(PocketStationError) as exc_info:
+        async with PocketStation.connect(
+            api_url="http://api.example.com",
+            relay_url="ws://relay.example.com",
+        ):
+            pass
+    assert exc_info.value.code == "http_error"
+
+
+@pytest.mark.asyncio
+async def test_given_preexisting_credentials_when_connect_then_no_http_call():
+    # Given — no network mock; any http call would error
+    creds = RoomCredentials.from_dict(VALID_ROOM_RESPONSE)
+    # When
+    async with PocketStation.connect(
+        api_url="http://should-not-be-called.example.com",
+        relay_url="ws://relay.example.com",
+        credentials=creds,
+    ) as session:
+        # Then — session uses provided credentials without making any HTTP call
+        assert session.room_id == "room-py-001"
+
+
+@pytest.mark.asyncio
+async def test_given_session_when_credentials_property_then_returns_room_credentials():
+    creds = RoomCredentials.from_dict(VALID_ROOM_RESPONSE)
+    async with PocketStation.connect(
+        api_url="http://unused.example.com",
+        relay_url="ws://relay.example.com",
+        credentials=creds,
+    ) as session:
+        assert isinstance(session.credentials, RoomCredentials)
+        assert session.credentials.room_id == "room-py-001"
diff --git a/tests/test_types.py b/tests/test_types.py
new file mode 100644
index 0000000..5613418
--- /dev/null
+++ b/tests/test_types.py
@@ -0,0 +1,54 @@
+"""Unit tests for pocketstation.types. Phase 5."""
+import pytest
+from pocketstation.types import IceServer, PocketStationError, RoomCredentials
+
+
+def test_given_valid_dict_when_from_dict_then_credentials_parsed():
+    # Given
+    data = {
+        "room_id": "room-abc",
+        "source_token": "src-tok",
+        "listener_token": "lst-tok",
+    }
+    # When
+    creds = RoomCredentials.from_dict(data)
+    # Then
+    assert creds.room_id == "room-abc"
+    assert creds.source_token == "src-tok"
+    assert creds.listener_token == "lst-tok"
+    assert creds.ice_servers == []
+
+
+def test_given_ice_servers_when_from_dict_then_parsed():
+    # Given
+    data = {
+        "room_id": "room-turn",
+        "source_token": "s",
+        "listener_token": "l",
+        "ice_servers": [
+            {"urls": ["stun:relay.example.com:3478"]},
+            {"urls": ["turn:relay.example.com:3478"], "username": "u", "credential": "p"},
+        ],
+    }
+    # When
+    creds = RoomCredentials.from_dict(data)
+    # Then
+    assert len(creds.ice_servers) == 2
+    assert creds.ice_servers[0].urls == ["stun:relay.example.com:3478"]
+    assert creds.ice_servers[1].username == "u"
+    assert creds.ice_servers[1].credential == "p"
+
+
+def test_given_pocketstation_error_when_raised_then_code_set():
+    # Given / When / Then
+    with pytest.raises(PocketStationError) as exc_info:
+        raise PocketStationError("connection failed", "network_error")
+    assert exc_info.value.code == "network_error"
+    assert "connection failed" in str(exc_info.value)
+
+
+def test_given_ice_server_when_constructed_then_fields_accessible():
+    srv = IceServer(urls=["stun:example.com:3478"])
+    assert srv.urls == ["stun:example.com:3478"]
+    assert srv.username is None
+    assert srv.credential is None