---
title: Migrating from AWS Step Functions
description: Move an AWS Step Functions state machine to the Workflow SDK by replacing JSON state definitions, Task states, Choice/Wait/Parallel states, Retry/Catch blocks, and .waitForTaskToken callbacks with Workflows, Steps, Hooks, and idiomatic TypeScript control flow.
type: guide
summary: Translate an AWS Step Functions state machine into the Workflow SDK with side-by-side code examples.
prerequisites:
  - /docs/getting-started/next
  - /docs/foundations/workflows-and-steps
related:
  - /docs/foundations/starting-workflows
  - /docs/foundations/errors-and-retries
  - /docs/foundations/hooks
  - /docs/foundations/streaming
  - /docs/deploying/world/vercel-world
---

# Migrating from AWS Step Functions



Move an AWS Step Functions state machine to the Workflow SDK by replacing JSON state definitions with TypeScript functions. This guide shows the direct mapping between ASL states and Workflow SDK primitives.

<Callout type="info">
  Install the Workflow SDK migration skill:

  ```bash
  npx skills add https://github.com/vercel/workflow --skill migrating-to-workflow-sdk
  ```
</Callout>

## Why migrate to the Workflow SDK

* Orchestration code is TypeScript, not JSON ASL. Transitions are `await`, branches are `if`/`switch`, and parallelism is `Promise.all`.
* Streaming is built in. Write durable progress from steps with `getWritable()` and named streams. No DynamoDB or SNS glue to surface status to clients.
* Infrastructure lives in one deployment. No separate state machine, per-task Lambda, IAM role wiring, or callback SQS queues.
* Error handling is TypeScript-native: step-level retries, `RetryableError`, and `FatalError` replace per-state Retry/Catch blocks.
* Agent-first tooling: the `npx workflow` CLI, `@workflow/ai` integration, and the Claude skill are available out of the box.

## What changes when you leave Step Functions?

AWS Step Functions defines workflows as JSON state machines using Amazon States Language (ASL). Each state (Task, Choice, Wait, Parallel, Map) is a node in a declarative graph. Lambda functions handle tasks, Retry/Catch blocks configure per-state error handling, and `.waitForTaskToken` manages callbacks.

The Workflow SDK replaces that JSON DSL with TypeScript. `"use workflow"` functions orchestrate `"use step"` functions in the same file. Branching is `if`/`else`. Waiting is `sleep()`. Parallelism is `Promise.all()`. Retries move down to the step level.

The migration replaces declarative configuration with idiomatic TypeScript and collapses the orchestrator and compute split. Business logic stays the same.

## Concept mapping

| AWS Step Functions                             | Workflow SDK                                 | Migration note                                               |
| ---------------------------------------------- | -------------------------------------------- | ------------------------------------------------------------ |
| State machine (ASL JSON)                       | `"use workflow"` function                    | The workflow function is the state machine.                  |
| Task state / Lambda                            | `"use step"` function                        | Side effects go in steps. No separate Lambda.                |
| Choice state                                   | `if` / `else` / `switch`                     | Native TypeScript control flow.                              |
| Wait state                                     | `sleep()`                                    | Import `sleep` from `workflow`.                              |
| Parallel state                                 | `Promise.all()`                              | Standard concurrency primitives.                             |
| Map state                                      | Loop + `Promise.all()` or child workflows    | Iterate with `for`/`map`.                                    |
| Retry / Catch                                  | Step retries, `RetryableError`, `FatalError` | Retry logic moves to step boundaries.                        |
| `.waitForTaskToken`                            | `createHook()` or `createWebhook()`          | Hooks for typed signals; webhooks for HTTP.                  |
| Child state machine (`StartExecution`)         | `"use step"` around `start()` / `getRun()`   | Return the `Run` object, await its result from another step. |
| Execution event history                        | Workflow event log                           | Same durable replay model.                                   |
| Progress via DynamoDB / SNS for client polling | `getWritable()` + named streams              | Stream durable updates; clients read from the stream.        |

<Callout type="info">
  `.waitForTaskToken` becomes `createHook()` or `createWebhook()`. Choice states become `if`/`else`. Map states become `Promise.all()`. Retry policies move from per-state configuration to step-level defaults.
</Callout>

## Translate your first workflow

Start with a single Task state. In ASL, even "call one Lambda" requires a state machine shell:

```json title="stateMachine.asl.json (Step Functions)"
"LoadOrder": {
  "Type": "Task",
  "Resource": "arn:aws:states:::lambda:invoke",
  "Parameters": { "FunctionName": "loadOrder", "Payload.$": "$" },
  "End": true
}
```

```typescript title="workflow/workflows/order.ts (Workflow SDK)"
export async function processOrder(orderId: string) {
  'use workflow'; // [!code highlight]
  return await loadOrder(orderId);
}

async function loadOrder(orderId: string) {
  'use step'; // [!code highlight]
  const res = await fetch(`https://example.com/api/orders/${orderId}`);
  return res.json() as Promise<{ id: string }>;
}
```

What changed: the ASL state machine and its Lambda collapse into two directive-tagged functions in one file.

### Adding a second step

In ASL, a second Task means a new state and a `"Next"` transition. In the Workflow SDK, it's another `await`:

```typescript
export async function processOrder(orderId: string) {
  'use workflow';
  const order = await loadOrder(orderId);
  await reserveInventory(order.id); // [!code highlight]
  return { orderId: order.id, status: 'reserved' };
}
```

`await` replaces `"Next"`. Each new step is a new function with `"use step"`; no additional deployment.

### Starting from an API route

Step Functions starts a run via `StartExecution` (AWS SDK or API Gateway integration). The Workflow SDK starts a run with `start()` from a route handler:

```typescript title="app/api/orders/route.ts"
import { start } from 'workflow/api';
import { processOrder } from '@/workflows/order';

export async function POST(request: Request) {
  const { orderId } = (await request.json()) as { orderId: string };
  const run = await start(processOrder, [orderId]); // [!code highlight]
  return Response.json({ runId: run.runId });
}
```

## Wait for an external signal

The minimal ASL for a callback is a Task with `.waitForTaskToken`:

```json title="approval.asl.json (Step Functions)"
"WaitForApproval": {
  "Type": "Task",
  "Resource": "arn:aws:states:::sqs:sendMessage.waitForTaskToken",
  "Parameters": {
    "QueueUrl": "https://sqs.us-east-1.amazonaws.com/123456789012/approvals",
    "MessageBody": {
      "refundId.$": "$.refundId",
      "TaskToken.$": "$$.Task.Token"
    }
  },
  "End": true
}
```

```typescript title="workflow/workflows/refund.ts (Workflow SDK)"
import { createHook } from 'workflow';

export async function refundWorkflow(refundId: string) {
  'use workflow';
  using approval = createHook<{ approved: boolean }>({ // [!code highlight]
    token: `refund:${refundId}:approval`,
  });
  return await approval;
}
```

What changed: no SQS queue, no task token, no callback Lambda. The hook suspends the workflow durably until it is resumed.

### Resuming the hook

Step Functions resumes by calling `SendTaskSuccess` with the task token. The Workflow SDK resumes by calling `resumeHook` with the hook's token:

```typescript title="app/api/refunds/[refundId]/approve/route.ts"
import { resumeHook } from 'workflow/api';

export async function POST(req: Request, { params }: { params: Promise<{ refundId: string }> }) {
  const { refundId } = await params;
  const { approved } = (await req.json()) as { approved: boolean };
  await resumeHook(`refund:${refundId}:approval`, { approved }); // [!code highlight]
  return Response.json({ ok: true });
}
```

### Branching on the result

In ASL, branching after the wait requires a Choice state. In TypeScript, it's just `if`/`else`:

```json title="approval.asl.json (Step Functions)"
"CheckApproval": {
  "Type": "Choice",
  "Choices": [
    { "Variable": "$.approved", "BooleanEquals": true, "Next": "Approved" }
  ],
  "Default": "Rejected"
}
```

{/* @skip-typecheck: continuation snippet */}

```typescript title="workflow/workflows/refund.ts (Workflow SDK)"
const { approved } = await approval;
if (approved) return { refundId, status: 'approved' }; // [!code highlight]
return { refundId, status: 'rejected' };
```

## Spawn a child workflow

In ASL, a parent machine calls `StartExecution` (usually via `.sync` or `.waitForTaskToken`) to launch a child. In the Workflow SDK, `start()` and `getRun()` are runtime APIs, so wrap them in `"use step"` functions. Returning the `Run` object from the spawn step lets workflow observability deep-link to the child run.

### Parent starts a child

```typescript title="workflow/workflows/parent.ts"
import { start } from 'workflow/api';

async function spawnChild(item: string) {
  'use step'; // [!code highlight]
  return start(childWorkflow, [item]);
}

export async function parentWorkflow(item: string) {
  'use workflow';
  const run = await spawnChild(item);
  return { childRunId: run.runId };
}
```

### Awaiting the child's result

Add a second step that wraps `getRun()` and awaits `returnValue`:

```typescript
import { getRun } from 'workflow/api';

async function collectResult(runId: string) {
  'use step'; // [!code highlight]
  const run = getRun(runId);
  return (await run.returnValue) as { item: string; result: string };
}
```

Then in the workflow: `const result = await collectResult(run.runId);`. The child workflow itself (`childWorkflow`) is defined elsewhere with `"use workflow"`.

## What you stop operating

Moving off Step Functions removes these surfaces from the application:

* ASL state machine JSON and its reference syntax.
* Per-task Lambda functions, their IAM roles, and CloudFormation/CDK wiring.
* Task-token delivery infrastructure (SQS queues, callback Lambdas).
* Separate progress channels (DynamoDB, SNS) for client-visible updates.
* CloudWatch and X-Ray configuration for orchestrator observability.

Workflow and step functions live in the same deployment as the application. State transitions are `await` calls. Progress streaming, retries, and observability are built in.

## Step-by-step first migration

Pick one state machine and migrate it end-to-end before touching the rest. The steps below describe the smallest viable path.

### Step 1: Install the Workflow SDK

Add the `workflow` runtime package.

```bash
pnpm add workflow
```

### Step 2: Rewrite the state machine as a `"use workflow"` function

Transitions become `await` calls. Control flow (`Choice`, `Wait`, `Parallel`, `Map`) becomes `if`/`switch`, `sleep`, `Promise.all`, and loops.

```ts title="workflows/order.ts"
export async function processOrder(orderId: string) {
  "use workflow"; // [!code highlight]
  const order = await loadOrder(orderId);
  if (order.total > 1000) await reviewManually(order);
  await chargePayment(order);
}
```

### Step 3: Move each Lambda into a step function

Inline the Lambda body into a function with `"use step"` on the first line. Step functions keep full Node.js access, so existing SDK calls work unchanged.

```ts
async function loadOrder(id: string) {
  "use step"; // [!code highlight]
  return fetch(`/api/orders/${id}`).then((r) => r.json());
}
```

### Step 4: Replace `.waitForTaskToken` with a hook

Swap the task-token callback Lambda for `createHook()`. Callers `resumeHook(token, payload)` instead of `SendTaskSuccess`.

### Step 5: Start runs from an API route

Delete the `StartExecution` call and IAM wiring. Launch runs directly from a route handler:

```ts title="app/api/orders/route.ts"
import { start } from "workflow/api";
import { processOrder } from "@/workflows/order";

export async function POST(req: Request) {
  const { orderId } = await req.json();
  const run = await start(processOrder, [orderId]);
  return Response.json({ runId: run.runId });
}
```

### Step 6: Retire the Step Functions infrastructure

Delete the ASL JSON, per-task Lambda deployments, IAM roles, and callback queues. Remove CloudWatch and X-Ray wiring used for orchestrator observability. Verify the run in `npx workflow web` before shipping.

## Quick-start checklist

* Replace the ASL state machine with a single `"use workflow"` function. Transitions become `await` calls.
* Convert each Task / Lambda into a `"use step"` function in the same file.
* Replace Choice states with `if`/`else`/`switch`.
* Replace Wait states with `sleep()` from `workflow`.
* Replace Parallel states with `Promise.all()`.
* Replace Map states with loops or `Promise.all()`. For large fan-outs, wrap `start()` in a step.
* Replace `StartExecution` child machines with `"use step"` wrappers around `start()` and `getRun()`.
* Replace `.waitForTaskToken` with `createHook()` (internal callers) or `createWebhook()` (HTTP callers).
* Move Retry/Catch to step boundaries using `maxRetries`, `RetryableError`, and `FatalError`.
* Use `getStepMetadata().stepId` as the idempotency key for external side effects.
* Stream progress from steps with `getWritable()` instead of polling DynamoDB or SNS.
* Deploy and verify runs end-to-end with built-in observability.


## Sitemap
[Overview of all docs pages](/sitemap.md)