Google Adk Session

Google ADK — Sessions & State

Core Concepts

• Session: A conversation between user and agent (contains events/messages)
• State: Key-value store attached to a session (persists across turns)
• SessionService: Backend that stores/retrieves sessions

Session Services

Basic Usage with Runner

from google.adk.agents import Agent
from google.adk.runners import Runner
from google.adk.sessions import InMemorySessionService
from google.genai import types

agent = Agent(
    name="my_agent",
    model="gemini-2.5-flash",
    instruction="You are a helpful assistant.",
)

session_service = InMemorySessionService()
runner = Runner(agent=agent, session_service=session_service, app_name="my_app")

# Create a session
session = await session_service.create_session(
    app_name="my_app",
    user_id="user_123",
)

# Run agent
message = types.Content(
    role="user",
    parts=[types.Part(text="Hello!")],
)

async for event in runner.run_async(
    session_id=session.id,
    user_id="user_123",
    new_message=message,
):
    if event.content and event.content.parts:
        print(event.content.parts[0].text)

SQLite Session Service

from google.adk.sessions.sqlite_session_service import SqliteSessionService

session_service = SqliteSessionService(db_url="sqlite:///./sessions.db")

Database Session Service (PostgreSQL)

from google.adk.sessions import DatabaseSessionService

session_service = DatabaseSessionService(
    db_url="postgresql+asyncpg://user:pass@localhost/mydb",
)

Vertex AI Session Service

from google.adk.sessions import VertexAiSessionService

session_service = VertexAiSessionService(
    project="my-gcp-project",
    location="us-central1",
)

Working with State

State is a dict attached to the session, accessible in tools and instruction providers.

Reading State (in instruction provider)

from google.adk.agents.readonly_context import ReadonlyContext

def dynamic_instruction(ctx: ReadonlyContext) -> str:
    user_name = ctx.state.get("user_name", "friend")
    history_count = ctx.state.get("interaction_count", 0)
    return f"You are helping {user_name} (interaction #{history_count + 1})."

Writing State (in tools)

from google.adk.tools.tool_context import ToolContext

def set_user_preference(key: str, value: str, tool_context: ToolContext) -> str:
    """Sets a user preference.

    Args:
        key: The preference key.
        value: The preference value.
    """
    prefs = tool_context.state.get("preferences", {})
    prefs[key] = value
    tool_context.state["preferences"] = prefs
    return f"Set {key} = {value}"

State Prefixes

def save_data(tool_context: ToolContext) -> str:
    """Example of different state scopes."""
    # Session state (default)
    tool_context.state["current_task"] = "researching"

    # App-level (persists across sessions)
    tool_context.state["app:total_queries"] = tool_context.state.get("app:total_queries", 0) + 1

    # User-level (persists for this user across sessions)
    tool_context.state["user:preferred_language"] = "python"

    # Temp (gone after this invocation)
    tool_context.state["temp:intermediate_result"] = "..."

    return "Data saved."

Session Lifecycle

# Create
session = await session_service.create_session(
    app_name="my_app",
    user_id="user_123",
    state={"initial_key": "initial_value"},  # Optional initial state
)

# Get
session = await session_service.get_session(
    app_name="my_app",
    user_id="user_123",
    session_id=session.id,
)

# List sessions for user
sessions = await session_service.list_sessions(
    app_name="my_app",
    user_id="user_123",
)

# Delete
await session_service.delete_session(
    app_name="my_app",
    user_id="user_123",
    session_id=session.id,
)

Key Rules

• State persists across invocations within the same session
• Use output_key on agents to automatically store their output in state
• State values must be JSON-serializable (strings, numbers, lists, dicts)
• Use state prefixes (app:, user:, temp:) for different persistence scopes
• InMemorySessionService loses all data on restart — use SQLite+ for persistence
• The CLI (adk web, adk run) uses InMemorySessionService by default

Related Skills

• google-adk-memory — Long-term memory across sessions
• google-adk-app — App pattern (wraps session + memory services)
• google-adk-deploy — Production deployment (persistent session services)