Session stores

Beta

The Agents API is in Beta. It can introduce breaking changes in minor version releases.

Session stores persist snapshots for server-managed agents. They are the storage layer behind sessionId and snapshotId resumption, 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 web apps that need a different database, cloud storage, centralized authorization, retention policies, or tenant-aware persistence that the built-in stores do not cover.

Most applications only pass a store to aix.WithSessionStore(store). The agent runtime calls the store when it creates a snapshot, resumes with aix.WithSessionID or aix.WithSnapshotID, serves Agent.GetSnapshot, Agent.GetLatestSnapshot, and Agent.WaitForSnapshot, starts detached work, or aborts an in-flight turn with Agent.Abort.

The snapshot record

Every store method reads or writes an aix.SessionSnapshot[State]. Both the built-in stores and a custom store move this value verbatim:

type SessionSnapshot[State any] struct {
    SnapshotID   string               `json:"snapshotId"`
    SessionID    string               `json:"sessionId,omitempty"`
    ParentID     string               `json:"parentId,omitempty"`
    State        *SessionState[State] `json:"state,omitempty"`
    Status       SnapshotStatus       `json:"status,omitempty"`
    FinishReason AgentFinishReason    `json:"finishReason,omitempty"`
    Error        *status.Error        `json:"error,omitempty"`
    CreatedAt    time.Time            `json:"createdAt"`
    UpdatedAt    time.Time            `json:"updatedAt,omitempty"`
    HeartbeatAt  *time.Time           `json:"heartbeatAt,omitempty"`
}

The runtime owns the meaning of SnapshotID, SessionID, ParentID, State, Status, FinishReason, Error, and HeartbeatAt. The store owns durable persistence: it must preserve SessionID across rewrites, and it must not advance UpdatedAt on a heartbeat-only refresh, so liveness stays distinct from state changes. SessionState[State] is described on Sessions and state.

Status is an aix.SnapshotStatus, a string with six constants: pending, aborting, completed, failed, aborted, expired. Terminal() reports whether a status is settled, which is every one except pending and aborting.

Important implementation details:

• The identifier field is SnapshotID.
• State is a pointer and is nil on a pending or aborting snapshot, because a detached invocation commits its state only when it settles. It is also nil on a metadata-only read. Check for nil before reading snap.State.Messages, snap.State.Custom, or snap.State.Artifacts.
• An empty Status should be treated as completed for backwards compatibility. SnapshotStatusExpired is not directly persisted; it is computed on read from a stale HeartbeatAt, while the underlying record remains pending or aborting.

Full field documentation is on pkg.go.dev.

Use an in-memory store

localstore.NewInMemorySessionStore keeps snapshots in process memory. It is fast, requires no setup, and implements aix.SnapshotSubscriber and aix.SnapshotMetadataReader, which makes it useful for testing background execution and abort behavior locally.

import (
    aix "github.com/firebase/genkit/go/ai/exp"
    "github.com/firebase/genkit/go/ai/exp/localstore"
    genkitx "github.com/firebase/genkit/go/genkit/exp"
)

store := localstore.NewInMemorySessionStore[SupportState]()

supportAgent := genkitx.DefineAgent(g, "supportAgent",
    aix.InlinePrompt{
        ai.WithSystem("Help customers understand their order status."),
    },
    aix.WithSessionStore(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 session created by one process is invisible to another.

The in-memory store does not have configuration options. If you need retention or tenant-scoped local files, use the file store.

Use a file-backed store

localstore.NewFileSessionStore 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.

store, err := localstore.NewFileSessionStore[SupportState](
    "./.genkit/snapshots/support",
    localstore.WithMaxPersistedChainLength(20),
    localstore.WithSnapshotPathPrefix(func(ctx context.Context) string {
        return tenantIDFromContext(ctx)
    }),
    localstore.WithPollInterval(time.Second),
)
if err != nil {
    // Fails if the snapshot directory cannot be created or an option is
    // invalid, such as a path prefix that escapes the store directory.
    log.Fatalf("open support store: %v", err)
}

NewFileSessionStore[State] returns (*localstore.FileSessionStore[State], error). The in-memory and Firestore constructors likewise return their concrete types, *localstore.InMemorySessionStore[State] and (*firebasex.FirestoreSessionStore[State], error). All of them satisfy aix.SessionStore[State], so hold one in a struct field or pass it around typed as the interface:

type Service struct {
    Store aix.SessionStore[SupportState]
}

Type the value concretely only when you need methods that a specific store adds.

Snapshots are written under the directory passed to NewFileSessionStore, inside a subdirectory named by the path prefix. Without the option, every session shares one global subdirectory. Each agent in go/samples/basic-agents keeps its own file store under ./.genkit/snapshots/<agent>/, so conversations survive a restart of the command-line client.

Use WithMaxPersistedChainLength to bound how many snapshots are retained in one parent chain. A value of 1 keeps only the latest snapshot in a chain. Omitting the option leaves pruning disabled. Pruning follows parent links, so sibling branches are pruned independently when they are extended.

Use WithSnapshotPathPrefix to scope reads and writes to a subdirectory. Return a stable tenant or user identity from context.Context so one caller cannot read another caller’s snapshots. Prefixes may contain / for nested directories, but values that escape the store directory are rejected. See Scope a store by tenant for where the identity in ctx comes from.

Use WithPollInterval to control how often the file store checks for status changes written by another process or store instance sharing the same directory. The default is one second. A value less than or equal to zero disables cross-process polling, so subscriptions observe only changes written through the same store instance.

The file store is safe for concurrent use inside one process, writes snapshots atomically with temporary files and rename, and implements aix.SnapshotSubscriber and aix.SnapshotMetadataReader. It is still a local filesystem store, so use a custom store when many app instances need to coordinate durable sessions.

Scope a store by tenant

Both WithSnapshotPathPrefix options take a func(ctx context.Context) string. The ctx they receive is the request context the handler built, so the tenant identity travels from the HTTP request into the store through the action context.

Populate the action context with genkit.WithContextProviders when you mount the routes:

import (
    "context"
    "net/http"

    "github.com/firebase/genkit/go/core"
    "github.com/firebase/genkit/go/genkit"
    genkitx "github.com/firebase/genkit/go/genkit/exp"
)

for _, route := range genkitx.AgentRoutes(supportAgent) {
    mux.HandleFunc(route.Pattern(), route.Handler(
        genkit.WithContextProviders(func(ctx context.Context, req core.RequestData) (core.ActionContext, error) {
            // Authenticate the request first, then return the identity it proved.
            return core.ActionContext{"tenantId": req.Headers["x-tenant-id"]}, nil
        }),
    ))
}

Read it back out inside the prefix function with core.FromContext:

func tenantIDFromContext(ctx context.Context) string {
    tenantID, _ := core.FromContext(ctx)["tenantId"].(string)
    if tenantID == "" {
        return "global"
    }
    return tenantID
}

The prefix is recomputed from context.Context on every store call, so there is no operator bypass. A privileged reader such as a support console or a back-office approval queue must authorize the operator first, then build a context whose prefix function resolves to the target tenant, and only then read:

ctx = core.WithActionContext(ctx, core.ActionContext{"tenantId": targetTenant})

snap, err := supportAgent.GetSnapshot(ctx, snapshotID)

Do the authorization check outside the prefix function. The prefix is a scoping mechanism, not an access-control check.

Concurrent turns on one session

The runtime does not serialize invocations that share a sessionId. Two concurrent turns both resume from the same latest snapshot and both commit, creating sibling snapshots with the same ParentID. The next GetLatestSnapshot returns whichever was created last, so the other turn’s changes stop being reachable without its snapshotId.

Serialize turns per session in your application: a per-session lock, a queue, or disabling the send button client-side. To detect a fork after the fact, compare the snapshotId you resumed from with AgentOutput.SnapshotID.

An *aix.Agent is read-only after definition and safe to share across goroutines. An *aix.AgentConnection is a single-owner value: do not call Output() from one goroutine while another iterates Receive().

Use a Firestore store

firebasex.NewFirestoreSessionStore 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 implements aix.SnapshotSubscriber for background execution and abort.

The store resolves its Firestore client from the Firebase plugin registered with the Genkit instance, so pass the Firebase plugin to genkit.Init before constructing the store.

import (
    "github.com/firebase/genkit/go/plugins/firebase"
    firebasex "github.com/firebase/genkit/go/plugins/firebase/exp"
)

g := genkit.Init(ctx,
    genkit.WithExperimental(),
    genkit.WithPlugins(&firebase.Firebase{ProjectId: "my-project"}),
)

store, err := firebasex.NewFirestoreSessionStore[SupportState](ctx, g,
    firebasex.WithCollection("genkit-sessions"),
    firebasex.WithSnapshotPathPrefix(func(ctx context.Context) string {
        return tenantIDFromContext(ctx)
    }),
)
if err != nil {
    // Fails if the Firebase plugin is not registered on g or the Firestore
    // client cannot be resolved.
    log.Fatalf("open Firestore store: %v", err)
}

supportAgent := genkitx.DefineAgent(g, "supportAgent",
    aix.InlinePrompt{
        ai.WithSystem("Help customers understand their order status."),
    },
    aix.WithSessionStore(store),
)

The State type parameter is the user-defined custom-state type carried in the session state; it must be JSON-serializable.

All options are optional:

• WithCollection sets the root collection that holds snapshot documents. It defaults to genkit-sessions. Two companion collections, <collection>-shards and <collection>-pointers, are derived from it for sharded checkpoint state and per-session pointers.
• WithSnapshotPathPrefix derives a per-tenant prefix from context.Context, such as an authenticated user or organization ID. When set, snapshots, shards, and pointers are nested under a tenant-scoped subcollection, so one tenant can never read another tenant’s snapshots even with a snapshot ID. The value must be a single valid Firestore document ID (no / separators) and stable for a snapshot’s lifetime, since every read recomputes it. An empty result falls back to global, which is also the default when the option is omitted.
• WithCheckpointInterval sets the number of turns between full-state checkpoints. Between checkpoints the store writes JSON Patch diffs; a larger value writes fewer full checkpoints but reconstructs over more diffs. The number of diff documents read or written per turn is bounded by this value rather than by total session length. Must be at least 1; defaults to 25.
• WithShardSize sets the maximum size in bytes of a single shard or diff document. Checkpoint state is split into chunks of this size, and any diff exceeding it is promoted to a sharded checkpoint, so no document approaches Firestore’s 1 MiB limit. Must be positive; defaults to 512 KiB.

The store picks up Application Default Credentials and the FIRESTORE_EMULATOR_HOST environment variable through the Firebase plugin, so the same code runs against the Firestore emulator for local testing.

Because it implements aix.SnapshotSubscriber over Firestore’s native real-time listeners, a status change such as an abort committed by one process is observed by the process running the detached turn even across instances, without polling. It also implements aix.SnapshotMetadataReader, so a read with aix.WithMetadataOnly() costs one document read where a full read reconstructs the state from its checkpoint shards and diff chain. The store 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 aix.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.

aix.SessionStore is the pair of smaller interfaces aix.SnapshotReader and aix.SnapshotWriter, so a custom store implements snapshot reading and writing:

type SessionStore[State any] interface {
    GetSnapshot(ctx context.Context, snapshotID string) (*aix.SessionSnapshot[State], error)
    GetLatestSnapshot(ctx context.Context, sessionID string) (*aix.SessionSnapshot[State], error)
    SaveSnapshot(
        ctx context.Context,
        snapshotID string,
        fn func(existing *aix.SessionSnapshot[State]) (*aix.SessionSnapshot[State], error),
    ) (*aix.SessionSnapshot[State], error)
}

• GetSnapshot loads a snapshot by exact ID.
• GetLatestSnapshot loads the most recently created snapshot for a session, whatever its status. Use CreatedAt for recency, not UpdatedAt, because heartbeat writes update liveness without changing the conversation state. If two snapshots have the same CreatedAt, break ties deterministically. Parent IDs are lineage metadata for this lookup, not how the latest session snapshot is resolved.
• SaveSnapshot must be atomic. In a database, run the read, callback, and write in one transaction or use optimistic concurrency with retries. The callback may return a snapshot to save, return nil, nil to skip the write, or return an error to fail the operation. Stores that retry on contention may call the callback more than once, so keep the callback free of external side effects.

The store owns identity. If snapshotID is empty, generate a fresh ID. If snapshotID is provided, persist that ID even if the callback returns a different one. Preserve a row’s existing session ID on update.

To support detached background work and abort, also implement aix.SnapshotSubscriber.

type SnapshotSubscriber interface {
    OnSnapshotStatusChange(ctx context.Context, snapshotID string) <-chan aix.SnapshotStatus
}

The channel should yield the current status when a subscription starts, then yield later status changes until the context is canceled. The runtime uses this to notice when an abort flips a pending snapshot to aborting, and WaitForSnapshot uses it to return as soon as a row settles. Yield a status whenever a save changes it, including a save that edits the row in place.

Stores that do not implement SnapshotSubscriber can still support server-managed state, snapshots, and GetLatestSnapshot. The runtime rejects detach attempts because it cannot signal background work to stop.

An abort is two guarded writes through SaveSnapshot: the flip from pending to aborting, and the finalize from aborting to aborted with the state. Heartbeats refresh HeartbeatAt on both statuses and change nothing else. Because each mutator checks the status it starts from, a store that runs the callback inside a transaction gets these transitions right for free.

A store may also implement aix.SnapshotMetadataReader, both methods or neither:

type SnapshotMetadataReader[State any] interface {
    GetSnapshotMetadata(ctx context.Context, snapshotID string) (*aix.SessionSnapshot[State], error)
    GetLatestSnapshotMetadata(ctx context.Context, sessionID string) (*aix.SessionSnapshot[State], error)
}

They serve reads made with aix.WithMetadataOnly(), which the runtime uses wherever it only needs to know where a row stands: waiting on a snapshot, deciding whether a background task can be continued. Return the row with State nil. Without the interface the runtime reads in full and drops the state, so the capability is a cost saving rather than a requirement.

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. Derive tenancy from context.Context and apply it consistently in every store method.

Index by snapshot ID and by session ID plus creation time. GetLatestSnapshot should be efficient because it is the common path for continuing a conversation by sessionId.

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