Session stores

Session stores persist snapshots for server-managed agents. They are the storage layer behind sessionId, snapshotId, loadChat(), snapshot reads, branching, background execution, and aborting detached work.

Use the Sessions and state guide first when you are deciding between server-managed and client-managed state. Use this page when you know the server should own state and need to choose or implement the persistence layer.

Choose a store

In-memory store for tests, demos, local examples, and single-process experiments.
File store for local development, prototypes, CLIs, and single-host apps that need snapshots to survive process restarts.
Firestore store for production apps on Google Cloud or Firebase that want a managed, multi-instance database without writing a store.
Custom store for production apps that need a different database, centralized authorization, or retention policies that the built-in stores do not cover.

Most applications only configure a store on the agent. The agent runtime calls the store when it creates a snapshot, resumes with sessionId or snapshotId, serves loadChat(), reads a snapshot, starts detached work, or aborts an in-flight turn.

Use an in-memory store

InMemorySessionStore keeps snapshots in process memory. It is fast, requires no setup, and supports status-change callbacks inside the same process, which makes it useful for testing background execution and abort behavior locally.

import { InMemorySessionStore } from 'genkit/beta';

const store = new InMemorySessionStore<SupportState>();

export const supportAgent = ai.defineAgent({
  name: 'supportAgent',
  system: 'Help customers understand their order status.',
  stateSchema: SupportStateSchema,
  store,
});

Do not use the in-memory store when conversations must survive a process restart or when multiple server instances need to share sessions. Each process gets its own isolated map, so a sessionId created by one process is invisible to another.

The in-memory store accepts one option:

const store = new InMemorySessionStore<SupportState>({
  rejectBranchingSessions: true,
});

rejectBranchingSessions makes sessionId lookup fail when a session has more than one leaf snapshot. This is useful during development when you want accidental branching to be obvious. Clients can always resume by exact snapshotId.

Use a file-backed store

FileSessionStore stores each snapshot as a JSON file. It is a good fit for local development and single-host deployments where you want persistent state without operating a database.

import { FileSessionStore } from 'genkit/beta';

const store = new FileSessionStore<SupportState>(
  './.genkit/snapshots/support',
  {
    maxPersistedChainLength: 20,
    snapshotPathPrefix: ({ context }) => context?.auth?.uid ?? 'anonymous',
    rejectBranchingSessions: true,
    snapshotWatchPollIntervalMs: 1000,
  },
);

Snapshots are written under the directory passed to the constructor. By default, they go under a global subdirectory. When you provide snapshotPathPrefix, the prefix determines the subdirectory for every read and write.

Use maxPersistedChainLength to bound how many snapshots are retained in one parent chain. This helps local stores avoid growing forever. Because snapshots are full checkpoints, pruning an old ancestor removes it as a resume point, but surviving snapshots remain loadable.

Use snapshotPathPrefix to scope reads and writes to a subdirectory. Return a stable, app-controlled tenant or user segment from options.context, and do not return raw user input. The prefix becomes part of a filesystem path, so normalize or encode identifiers before returning them.

Use snapshotWatchPollIntervalMs to control the polling fallback for file watching. The file store uses directory watching plus polling to observe status changes, which helps one process notice an abort or completion written by another process sharing the same snapshot directory. The default is 2000 milliseconds.

The file store serializes writes per snapshot file and writes by renaming a temporary file into place. That helps avoid torn JSON files when concurrent reads happen during a write. It does not turn the filesystem into a multi-instance production database, so use a custom store when many app instances need to coordinate durable sessions.

Use a Firestore store

FirestoreSessionStore persists snapshots in Cloud Firestore. It is a managed, multi-instance store, so it is the built-in option for production apps where several server instances share sessions, and it supports snapshot watching for background execution and abort.

It ships in two packages with the same API. Use @genkit-ai/google-cloud on Google Cloud, or @genkit-ai/firebase when you already have a Firebase Admin app. Both export from the /beta entry point.

import { FirestoreSessionStore } from '@genkit-ai/google-cloud/beta';

const store = new FirestoreSessionStore<SupportState>({
  collection: 'genkit-sessions',
  snapshotPathPrefix: (options) => options?.context?.auth?.uid ?? 'global',
});

export const supportAgent = ai.defineAgent({
  name: 'supportAgent',
  system: 'Help customers understand their order status.',
  stateSchema: SupportStateSchema,
  store,
});

All options are optional:

db is an explicit Firestore instance. It defaults to a new client that picks up Application Default Credentials and the FIRESTORE_EMULATOR_HOST environment variable.
collection is the collection that holds snapshot documents. It defaults to genkit-sessions. Two companion collections, <collection>-pointers and <collection>-shards, are derived from it for per-session pointers and sharded state.
snapshotPathPrefix returns a per-tenant prefix from the call’s SessionStoreOptions, such as the authenticated user ID from options.context. When set, snapshots, pointers, and shards are nested under a tenant-scoped subcollection, so one tenant can never read another tenant’s snapshots even with a snapshotId. It defaults to global.
checkpointInterval is the number of turns between full-state checkpoints. Between checkpoints the store writes diffs. A larger value writes fewer full snapshots but reconstructs over more diffs. It defaults to 25.
shardSize is the maximum size in bytes of a single shard or diff document. State is split into chunks of this size so no document approaches Firestore’s 1 MiB limit. It defaults to 512 KiB.

On Firebase, import from @genkit-ai/firebase/beta instead and pass firebaseApp to derive the Firestore instance from an existing Admin app:

import { FirestoreSessionStore } from '@genkit-ai/firebase/beta';

const store = new FirestoreSessionStore<SupportState>({
  firebaseApp: app,
  collection: 'genkit-sessions',
});

The Firestore store watches snapshot documents to observe status changes, so background execution and aborts work across instances without polling. It does not prune snapshots, so plan retention for long-running or artifact-heavy conversations as described in Production guidance.

Implement a production store

When the built-in Firestore store does not fit, implement a custom SessionStore so snapshots live in your own production data layer. This is the right approach for Cloud SQL, Spanner, Postgres, Redis-backed systems with durability, or application-specific storage that already handles user and tenant authorization.

A custom store implements three capabilities:

getSnapshot() loads either one exact snapshot or the latest snapshot for a session.
saveSnapshot() applies an atomic read-modify-write.
onSnapshotStateChange() lets the runtime observe status changes for abort and background work.

import type {
  SessionSnapshot,
  SessionStore,
  SessionStoreOptions,
  SnapshotMutator,
} from 'genkit/beta';

type SnapshotLookup = {
  snapshotId?: string;
  sessionId?: string;
  context?: SessionStoreOptions['context'];
};

class DatabaseSessionStore<S> implements SessionStore<S> {
  async getSnapshot(
    opts: SnapshotLookup,
  ): Promise<SessionSnapshot<S> | undefined> {
    // Load by opts.snapshotId, or load the latest leaf for opts.sessionId.
    throw new Error('Not implemented');
  }

  async saveSnapshot(
    snapshotId: string | undefined,
    mutator: SnapshotMutator<S>,
    options?: SessionStoreOptions,
  ): Promise<string | null> {
    // Atomically read the current snapshot, call mutator, and persist the result.
    throw new Error('Not implemented');
  }

  onSnapshotStateChange(
    snapshotId: string,
    callback: (snapshot: SessionSnapshot<S>) => void,
    options?: SessionStoreOptions,
  ): void | (() => void) {
    // Optional, but needed for responsive abort and background status updates.
  }
}

getSnapshot() must support exactly one lookup mode at a time:

snapshotId loads that exact snapshot.
sessionId loads the latest leaf snapshot for that session.

Here, “latest” means the latest leaf snapshot in the session history. A leaf is a snapshot that no other snapshot references as its parent. If branching exists, the built-in stores either select the most recently created leaf or throw when rejectBranchingSessions is enabled.

saveSnapshot() must be atomic. In a database, wrap the read, mutator call, and write in a transaction or use optimistic concurrency with retries. The mutator may return a snapshot to save, return null to skip the write, or throw to fail the operation. If your retry logic can call the mutator more than once, keep the mutator invocation free of external side effects.

When snapshotId is undefined, the store should assign a new snapshot ID. When a snapshot ID is provided, the store should write that ID even if the mutator returns a different one.

Implement onSnapshotStateChange() when detached background work should respond quickly to aborts or when clients should observe status changes without polling. Return an unsubscribe function when the store opens a listener, subscription, or timer. If a custom store omits this method, normal server-managed state still works, but background abort behavior is limited.

Production guidance

Store snapshots as sensitive user data. They can contain message history, custom state, artifacts, tool inputs, and generated outputs.

Scope every read and write by authenticated user, organization, or tenant. Do not rely on snapshot IDs alone as authorization. Use SessionStoreOptions.context to pass request context into store operations.

Index by snapshot ID, session ID, parent ID, and creation time. sessionId lookup should be efficient because it is the common path for continuing a conversation. Parent relationships matter for leaf selection.

Plan retention before launch. Snapshots are full conversation checkpoints, so long-running conversations and artifact-heavy agents can grow quickly.