workflow/docs/worlds/vercel.mdx

Workflow SDK - Build durable, resilient, and observable workflows

---
title: Vercel World
description: Fully managed World for Vercel deployments with automatic storage, queuing, and authentication.
type: integration
summary: Deploy workflows to Vercel with fully managed storage, queuing, and authentication.
prerequisites:
  - /docs/deploying
related:
  - /docs/how-it-works/encryption
  - /worlds/local
  - /worlds/postgres
---

The Vercel World is a fully managed workflow backend for applications deployed on Vercel. It provides scalable storage, distributed queuing, and automatic authentication without configuration.

When you deploy to Vercel, workflows automatically use the Vercel World without requiring setup.

## Usage

Deploy your application to Vercel:

```bash
vercel deploy
```

Vercel automatically:

- Selects the Vercel World backend
- Configures authentication using OIDC tokens
- Provisions storage and queuing infrastructure
- Isolates data per environment (production, preview, development)

<FluidComputeCallout />

## System environment variables

Workflow recognizes a Vercel deployment by `VERCEL_DEPLOYMENT_ID`. Vercel exposes that variable, along with the rest of its [system environment variables](https://vercel.com/docs/environment-variables/system-environment-variables), only when the project opts in. Check this before your first deployment:

1. Open your project in the [Vercel dashboard](https://vercel.com/dashboard).
2. Go to **Settings**, then **Environment Variables**.
3. Select the **Enable access to System Environment Variables** checkbox.
4. Redeploy. The setting applies to new deployments; it does not change deployments that already exist.

`VERCEL_DEPLOYMENT_ID` is available at both build time and runtime, and Workflow reads it in both. The build uses it to decide whether to emit Vercel Function output, including the queue-triggered flow handler, or local development output. The runtime uses it to [select the World](/docs/configuration/worlds#workflow_target_world).

<Callout type="warn">
  With the checkbox cleared, a Vercel deployment is indistinguishable from a
  non-Vercel environment as far as Workflow is concerned: the build emits local
  output and, unless `WORKFLOW_TARGET_WORLD` is set, the runtime selects the
  [Local World](/worlds/local), which stores workflow state on the filesystem.
  A deployment's filesystem is read-only, so with this default selection,
  every run fails before its first step.
</Callout>

### Diagnosing a missing deployment ID

With no `WORKFLOW_TARGET_WORLD` override, nothing in the deployment announces the wrong World, so the failure is easy to mistake for a bug in the SDK:

- Runs fail with the Local World reporting that it cannot create its data directory, naming a filesystem code such as `EROFS`.
- No runs appear in the Vercel dashboard, because none were ever created in the Vercel World.
- The SDK's "the local (filesystem) world is running inside a Vercel deployment" warning does **not** appear. That check keys off `VERCEL_DEPLOYMENT_ID` as well, so the same missing variable hides it.

To confirm, log `process.env.VERCEL_DEPLOYMENT_ID` from a deployed function. If it is undefined (as is `VERCEL`), the setting is off.

Setting `WORKFLOW_TARGET_WORLD=vercel` is not a workaround. The Vercel World needs the deployment ID itself, to address queue messages to the deployment that created each run and to derive that deployment's encryption keys, so it fails with an error naming the missing `VERCEL_DEPLOYMENT_ID`. Enable the checkbox and redeploy.

## Vercel platform documentation

For complete details on pricing, usage limits, and included allotments on Vercel, see the official Vercel documentation:

- **[Vercel Workflow](https://vercel.com/docs/workflows)**: Pricing details, concepts, and observability for Workflow on Vercel
- **[Vercel limits](https://vercel.com/docs/limits)**: Platform-wide limits, including Workflow-specific constraints
- **[Vercel Hobby plan](https://vercel.com/docs/plans/hobby)**: Free-tier included usage for Workflow and other resources

For self-hosted deployments, use the [Postgres World](/worlds/postgres). For local development, use the [Local World](/worlds/local).

## Per-run limits

The Vercel World caps how large a single run can get. It caps the run's [event log](/docs/how-it-works/event-sourcing), and separately caps how many steps one run may create; see [Workflow run limits](https://vercel.com/docs/workflows/pricing#workflow-run-limits) for the current values. A run that exhausts its event budget fails with `MAX_EVENTS_EXCEEDED` and cannot be continued.

Treat both caps as backstops, not budgets. Replay cost grows with the log, so a run slows down well before it fails. We recommend splitting a run into [child workflows](/cookbook/advanced/child-workflows) once a run would grow past a few thousand events. Size for that recommendation rather than for the cap.

Vercel raises the per-run event and step limits on request, so an unusually large run that genuinely cannot be split is worth raising with support rather than working around.

## Multi-region

The Vercel World runs in every [Vercel Function region](https://vercel.com/docs/regions). Each workflow run is pinned to a single region at creation time. Its stored state, queue dispatch, and streams are all served from that region without cross-region round trips on the hot path. When your application is deployed in the run's region, as described below, step execution is also region-local.

<Callout type="info">
  Multi-region requires `workflow` version **5.0.0** or later. The 4.x
  release line does not support region pinning. Runs created by 4.x always
  live in `iad1`.
</Callout>

### Automatic region pinning

No configuration is needed. A run is pinned to the region of the function that creates it:

- Deploy your app to a single region (via [`regions`](https://vercel.com/docs/project-configuration/vercel-json#regions) in `vercel.json` or the project settings), and every run lives there.
- Deploy to multiple regions for a globally distributed audience, and each run is pinned to the region that served the user who triggered it. Workflow data and streaming stay close to that user.

### Explicit region selection

To pin a specific run somewhere else, pass the `region` option to [`start()`](/docs/api-reference/workflow-api/start):

```typescript
import { start } from "workflow/api";
import { myWorkflow } from "@/workflows/my-workflow";

const run = await start(myWorkflow, [input], { region: "sfo1" });
```

<Callout type="warn">
  The `region` option controls where the run's **data is stored** and where
  its **queue messages are dispatched from**. It does not deploy your code
  there. Your workflow and step functions execute in the regions your
  application is deployed to. For execution to actually happen in the
  specified region, your app must be deployed there through
  [`regions`](https://vercel.com/docs/project-configuration/vercel-json#regions) in
  `vercel.json` or the Function Regions setting in your project settings.
  If it isn't, the run's data lives in the requested region but its steps
  execute in the nearest region your app is deployed to.
</Callout>

### Good to know

- Reads, hook resumes, and stream consumers can come from anywhere. The platform routes them to the run's region automatically.
- Runs created by 4.x SDKs, including runs that existed before you upgraded, live in `iad1` and are unaffected by an upgrade. There is no migration.
- **Hook tokens are currently stored in `iad1`** for every run, regardless of the run's region. The token-to-run mapping that powers [`getHookByToken()`](/docs/api-reference/workflow-api/get-hook-by-token) and [`resumeHook()`](/docs/api-reference/workflow-api/resume-hook) lives there so tokens without region information can always be resolved. Hook *payloads* are not affected. A received payload is recorded on the run's event log, which lives in the run's region like all other run data. This token placement may become a project-level setting in the future.

## Limitations

- **No run migration**: A run's region is fixed at creation. Existing runs cannot be moved to a different region.
- **Hook minimum retention**: [`experimental_minRetention`](/docs/api-reference/workflow/create-hook#keep-a-token-unavailable-after-the-run-ends) cannot exceed 30 days.

## Observability

Workflow observability is built into the Vercel dashboard on your project page. It respects your existing authentication and project permission settings.

The Vercel World implements the optional [`world.analytics`](/docs/api-reference/workflow-runtime/world/analytics) interface, backed by the same observability data pipeline as the dashboard. Two behaviors are specific to this implementation. Listings scan faster when bounded with a `startTime`/`endTime` window, and your plan's observability lookback caps the queryable window. Requesting an older window fails with `observability-upgrade-required`, and responses include `pageInfo` with the current and maximum lookback so tools can size date ranges.

The `workflow` CLI commands open a browser window deeplinked to the Vercel dashboard:

```bash
# List workflow runs (opens Vercel dashboard)
npx workflow inspect runs --backend vercel

# Launch the web UI (opens Vercel dashboard)
npx workflow web --backend vercel
```

The CLI automatically retrieves authentication from the Vercel CLI (`vercel login`) and infers project/team IDs from your local Vercel project linking.

To use the local observability UI instead of the Vercel dashboard:

```bash
npx workflow web --backend vercel --localUi
```

To override the automatic configuration:

```bash
npx workflow inspect runs \
  --backend vercel \
  --env production \
  --project my-project \
  --team my-team \
  --authToken <your-token>
```

Learn more in the [Observability](/docs/observability) documentation.

## Testing & compatibility

<WorldTestingPerformance worldId="vercel" />

## Configuration

In a Vercel deployment, you do not configure the Vercel World yourself. The platform injects everything the runtime needs, including `VERCEL_DEPLOYMENT_ID`, `VERCEL_PROJECT_ID`, per-request OIDC tokens, and `VERCEL_DEPLOYMENT_KEY` for encryption.

Do not set those platform-provided values yourself. You do have to leave [system environment variables](#system-environment-variables) enabled for the project, though: that setting is what makes `VERCEL_DEPLOYMENT_ID` available in the first place.

Most users never need to set the `WORKFLOW_VERCEL_*` variables below. They are only overrides for tools running outside Vercel, such as your laptop or CI, when those tools need to inspect or test a remote Vercel Workflow project and cannot infer the project, team, token, or target environment automatically.

For example, you might set them when running `workflow inspect runs --backend vercel` from CI without an interactive `vercel login`, or when running tests against a specific preview deployment. In normal local development, the CLI infers these values from your `.vercel` directory and Vercel CLI login. In a deployed Vercel function, these variables have no effect on runtime configuration, and the runtime warns if they are set there.

### `WORKFLOW_VERCEL_ENV`

The Vercel environment to target. Options: `production`, `preview`. Default: `production`.

### `WORKFLOW_VERCEL_AUTH_TOKEN`

Vercel API authentication token. Keep this secret in your environment, not in code. Falls back to `VERCEL_TOKEN`, then to your Vercel CLI login.

### `WORKFLOW_VERCEL_PROJECT`

Vercel project ID (`prj_...`).

### `WORKFLOW_VERCEL_PROJECT_NAME`

Vercel project name/slug, used for dashboard links.

### `WORKFLOW_VERCEL_TEAM`

Vercel team ID.

### `WORKFLOW_VERCEL_BACKEND_URL`

Custom base URL for the Vercel workflow API proxy. Default: `https://api.vercel.com/v1/workflow`.

### `VERCEL_WORKFLOW_SERVER_URL`

Custom workflow-server URL for direct runtime requests, or for the proxy to forward to via `WORKFLOW_VERCEL_BACKEND_URL`. Default: unset; normal deployments should not need this.

### `WORKFLOW_SEQUENTIAL_REPLAYS`

Set `WORKFLOW_SEQUENTIAL_REPLAYS=1` to guarantee that **at most one orchestrator (flow) invocation runs at a time per workflow run**. This behavior is off by default; without it, the runtime relies on idempotency and the event log to tolerate concurrent flow invocations of the same run.

When enabled, each run's orchestrator messages are given their own queue topic and the flow trigger is configured with `maxConcurrency: 1`, so [Vercel Queues](https://vercel.com/docs/queues) processes replays for a given run strictly one at a time. Step executions (which ride the flow topic in the combined handler model) get a per-step topic, so steps keep full parallelism.

<Callout type="warn">
  This variable is read at **both build time and runtime**, so it must be set as a project-level environment variable that applies to your build and your deployed functions. Setting it for only one will produce an inconsistent configuration. The same applies to framework integrations that write their own queue trigger configuration instead of using `getWorkflowQueueTrigger()` from `@workflow/builders`: they only get the runtime half (per-run topics) unless they also emit `maxConcurrency: 1` on their flow trigger.
</Callout>

Because it routes each run's flow invocations through a dedicated `maxConcurrency: 1` queue topic, enabling this might lead to higher queue performance overhead.

### `VERCEL_QUEUE_MAX_DELAY_SECONDS`

Maximum delay, in seconds, that Workflow uses for one Vercel Queues continuation message when implementing `sleep()`. If a workflow sleeps longer than this, the runtime schedules another continuation message when the first one fires, repeating until the sleep's target time is reached. Default: `82800` (23 hours).

Vercel Queues can delay messages for up to 7 days, capped by the message TTL. Because the default TTL is 24 hours, Workflow uses a 23-hour continuation hop to stay safely inside that default.

### `WORKFLOW_REQUEST_TIMEOUT_MS`

Per-request timeout, in milliseconds, for Vercel World HTTP calls to workflow-server. Default: `60000`. Clamped to `10000`-`120000`; a value outside that range is pulled into it and warns once.

Below the floor the deadline starts canceling requests that would have succeeded, since a cold route or a large event page can take seconds, and a canceled request is redriven through the queue rather than making progress. The ceiling matches the longest a backend route holds a response. Requests that legitimately outlast it (stream reads and writes, event batches) opt out of the deadline entirely rather than relying on this value.

### `WORKFLOW_MAX_CHUNKS_PER_REQUEST`

Maximum stream chunks written in one Vercel World request. Larger batches are split across multiple requests. Default: `1000`. Minimum: `1`.

### `WORKFLOW_STREAMS_TRANSPORT`

Stream writes upgrade to a WebSocket (`workflow-stream-ws/v1`) instead of one HTTP request per write group. Default: `ws`.

Set `WORKFLOW_STREAMS_TRANSPORT=http` to opt out. That value is matched case-insensitively and ignoring surrounding whitespace; any other value, including unset, empty, or `ws`, uses the WebSocket. Stream reads always use HTTP.

The setting is ignored when the World is configured with `projectConfig` and routes through the `api-workflow` proxy, which does not forward a WebSocket upgrade, so stream writes stay on HTTP.

The client only offers the upgrade. The server accepts or declines each one, and a writer whose upgrade is declined or fails writes over HTTP for the rest of its lifetime. This setting does not decide which tenants may upgrade and does not infer server support from package versions. The protocol route (`/websockets/v1`) is versioned independently from REST v2/v4 and persisted workflow `specVersion` values.

A writer's first write group always goes over HTTP, and so does its second. The socket starts opening in the background once the second group's request is sent, and later groups keep going over HTTP until it opens, so no write waits for the upgrade. A writer that closes after one or two groups never uses the socket. If the socket has not opened within 10 seconds, or the upgrade fails or is declined, the writer stays on HTTP.

Writes and close requests execute serially, so a write never overtakes an earlier one on the other transport. After the socket accepts a write, a missing acknowledgement has an unknown outcome: the writer fails rather than replaying the write over HTTP and risking a duplicate append. A throttled (429) write or close did not apply, so the writer retries it after the server's `Retry-After`, as the HTTP writer does, on the socket if it stays open (or its replacement, after a drain) and otherwise over HTTP. Past 30 seconds of cumulative wait, the write moves to HTTP, whose own 429 retry applies. A close that fails with a 5xx is retried over HTTP, since close is idempotent.

Once a released writer's writes drain, its socket closes without closing the shared stream, and later writes through that same handle go over HTTP. Writers acquired with `getWritable()` inside a step release their socket when the step completes. External `getRun(runId).getWritable()` handles release it on the first `releaseLock()` after pending writes drain, so hold the writer lock for the whole burst to keep writing over the socket.

Before routine authentication expiry or server max duration, the server sends a v1 `drain` control. The client stops sending, lets an already-admitted request receive its reply, and reconnects after the server closes with code 1001. If the new socket is not open within 250 ms, the writer continues over HTTP. Authentication drains re-resolve a fresh bearer. A request that was sent but receives no reply before close still has an unknown outcome and is never replayed.

The server sends WebSocket pings to keep an idle socket open, and the client must answer them. The `ws` library the Vercel World uses answers pings automatically, so there is nothing to configure.

Each stream WebSocket message is at most [`WORKFLOW_WS_MAX_MESSAGE_BYTES`](#workflow_ws_max_message_bytes) bytes. A write group larger than the limit is sent as several ordered write requests. A single chunk too large for one message is written over HTTP instead, as are the rest of its writer's writes.

### `WORKFLOW_EVENTS_TRANSPORT`

Workflow run events ship to the Vercel World over a WebSocket instead of one HTTP request each. Default: `ws`.

Set `WORKFLOW_EVENTS_TRANSPORT=http` to opt out. Only that exact value disables the WebSocket — any other value, including unset or empty, takes it — so a typo fails toward the default rather than silently pinning a deployment to HTTP.

The setting is ignored when the World is configured with `projectConfig` and therefore routes through the `api-workflow` proxy: that endpoint is an HTTP-only REST gateway and does not forward a WebSocket upgrade, so events stay on HTTP. The fallback is silent — now that the WebSocket is the default, nothing asked for it — and is reported once per process under `DEBUG=workflow:*`. `workflow.events.transport` on the per-write span records which transport actually carried a run.

Event writes use the WebSocket only while that run's events channel is open. The queue handler opens it for every delivery, so workflows need nothing extra. Code that writes a run's events outside a delivery, such as a custom driver or a long-lived process, opens the channel with `openEventsChannel(runId)`, or those writes go over HTTP. Call the returned release when you're done, because an open socket keeps the process alive:

{/*@skip-typecheck: incomplete code sample*/}

```typescript title="write-events.ts" lineNumbers
import { createWorld, openEventsChannel } from "@workflow/world-vercel";

const world = createWorld();
const release = openEventsChannel(runId);
try {
  await world.events.create(runId, event);
} finally {
  release?.();
}
```

`openEventsChannel()` returns `undefined`, and writes stay on HTTP, when the transport is disabled or the World cannot hold a socket, such as a `projectConfig` World.

Tracing is unaffected by the choice. Each event write emits an `http POST` client span against the same `url.full`, regardless of which transport carries it. On the WebSocket path, the span is synthesized around the frame because no HTTP request is made. Attributes distinguish the transports:

| Attribute | HTTP | WebSocket |
| --- | --- | --- |
| `workflow.events.transport` | `http` | `ws` |
| `workflow.event.type` | the event type, e.g. `step_started` | same |
| `network.protocol.name` | — | `websocket` |
| `workflow.events.ws.url` | — | the socket the frame went over |
| `workflow.events.ws.req_id` | — | per-connection request id, matching the server's log line |
| `workflow.events.ws.request_parts` | — | messages the request was sent as, when it was split |
| `workflow.events.ws.reply_parts` | — | messages the reply arrived as, when it was split |

The WebSocket handshake is itself a span, `workflow.events.ws.connect`, so the cost of opening (or eagerly reopening) a connection is attributable rather than showing up as unexplained time inside the first write.

### `WORKFLOW_EVENTS_TRANSPORT_WS_OVERRIDE_WORKFLOWS`

Comma-separated workflows whose runs use the WebSocket events transport even when [`WORKFLOW_EVENTS_TRANSPORT`](#workflow_events_transport) is `http`. Use it to move selected workflows onto the WebSocket while the rest of the deployment stays on HTTP. Default: none.

Each entry is a workflow's function name, such as `processOrder`, or its full workflow name, such as `workflow//./src/workflows/order//processOrder`. Matching is exact and case-sensitive. A function name matches every workflow with that name, in any file.

```bash
WORKFLOW_EVENTS_TRANSPORT_WS_OVERRIDE_WORKFLOWS=processOrder,syncInventory
```

The override applies to the events channel the queue handler opens for each delivery of a listed workflow's run. The workflow name comes from the delivery's queue, so it covers the run's workflow and step invocations alike. `openEventsChannel(runId, config, { workflowName })` applies it to channels you open yourself; without `workflowName`, a deployment with `WORKFLOW_EVENTS_TRANSPORT=http` opens none. Unless `WORKFLOW_EVENTS_TRANSPORT=http` is set, every workflow already uses the WebSocket and the override has no effect.

Like other environment variables, the setting is fixed for each deployment, and a run stays on the deployment it started on. Changing it takes effect for runs started on the next deployment; runs already in progress keep the transport of the deployment they're pinned to.

### `WORKFLOW_WS_MAX_MESSAGE_BYTES`

Largest WebSocket message the Vercel World sends, header included, on both the events and stream-write transports. Default: `12582912` (12 MiB).

Some WebSocket paths limit the size of a single message, commonly to 16 MiB. Event payloads can be larger: a step's input or output is carried inside its event. A frame over this limit is sent as several messages, and the other side rebuilds it before handling it. Stream writes split a large write group into several ordered write requests instead (see [`WORKFLOW_STREAMS_TRANSPORT`](#workflow_streams_transport)). Frames at or under the limit are unaffected. Integer values are clamped to `2097152`-`16777216` (2–16 MiB) with a warning; other values use the default.

The client splits its own large requests, which needs a Vercel World backend that accepts split frames. It lists `frame-parts` in the `x-workflow-ws-flags` header of the WebSocket upgrade, and the backend splits large replies only for a client that does, so older clients keep receiving whole replies.

### Programmatic configuration

`createWorld()` accepts explicit API configuration. It does not read `WORKFLOW_VERCEL_*` automatically, so pass the environment values yourself when you want a configured World module:

{/*@skip-typecheck: incomplete code sample*/}

```typescript title="my-world.ts" lineNumbers
import { createWorld } from "@workflow/world-vercel";

export default createWorld({
  token: process.env.WORKFLOW_VERCEL_AUTH_TOKEN,
  projectConfig: {
    projectId: "prj_...",
    teamId: "team_...",
    environment: "production",
  },
});
```

```bash title=".env"
WORKFLOW_TARGET_WORLD="./my-world.ts"
```

## Versioning

On Vercel, workflow runs are pegged to the deployment that started them. This means:

- Existing workflow runs continue executing on their original deployment, even as new code is deployed
- New workflow runs start on the latest deployment
- Code changes won't break in-flight workflows

This ensures long-running workflows complete reliably without being affected by subsequent deployments.

For the full model, including rerunning on latest and explicit upgrade boundaries, see [Versioning](/docs/foundations/versioning).

## Security

### Consumer function security

Workflow handler functions on Vercel are not accessible through public endpoints. During the build step, the Workflow SDK registers the combined flow handler as only reachable by [Vercel Queue](https://vercel.com/docs/queues), using the `experimentalTriggers` configuration in `.vc-config.json`:

```json title=".vc-config.json (flow handler)"
{
  "experimentalTriggers": [
    {
      "type": "queue/v2beta",
      "topic": "__wkf_workflow_*",
      "consumer": "default",
    }
  ]
}
```

Practically, this means:

- You don't need to add authentication or authorization logic to workflow handlers
- Unauthorized requests can never reach workflow or step execution
- Only messages delivered through Vercel Queues can trigger execution
- Handlers receive only a message ID that must be retrieved from Vercel's backend, making it impossible to craft custom payloads

<Callout>
  The Workflow SDK build step manages this configuration. If you are writing a custom integration, see [Framework integrations: Security](/docs/how-it-works/framework-integrations#security) for more details.
</Callout>

## How it works

The Vercel World uses Vercel's infrastructure for workflow execution:

- **Storage**: Workflow data is stored in Vercel's cloud with automatic replication and [end-to-end encryption](/docs/how-it-works/encryption)
- **Queuing**: Steps are distributed across Vercel Functions through [Vercel Queues](https://vercel.com/docs/queues) with automatic retries and [consumer function security](#consumer-function-security)
- **Authentication**: OIDC tokens provide secure, automatic authentication

For more details, see the [Vercel Workflow documentation](https://vercel.com/docs/workflows).