Migrating from v1

Alchemy v1 uses async/await with top-level await for orchestration. Alchemy v2 replaces this with Effect generators for type-safe error handling, composable retries, and declarative resource wiring.

Your existing async fetch handlers do not need to change — you can keep them as-is and still get all the benefits of the new engine.

Step 1: Replace the Stack

In v1, you create an app with await alchemy(...) and finalize it at the end:

// v1 — alchemy.run.ts
import alchemy from "alchemy";
import { Worker, Bucket } from "alchemy/cloudflare";

const app = await alchemy("my-app", {});

const bucket = await Bucket("bucket", {});
const worker = await Worker("worker", {
  entrypoint: "./src/worker.ts",
  bindings: { BUCKET: bucket },
});

console.log(worker.url);

await app.finalize();

In v2, you export a default Alchemy.Stack and use yield* instead of await:

// v2 — alchemy.run.ts
import * as Alchemy from "alchemy";
import * as Cloudflare from "alchemy/Cloudflare";
import * as Effect from "effect/Effect";

export const Bucket = Cloudflare.R2.Bucket("Bucket");

export const Worker = Cloudflare.Worker("Worker", {
  main: "./src/worker.ts",
  env: { Bucket },
});

export default Alchemy.Stack(
  "MyApp",
  { providers: Cloudflare.providers(), state: Cloudflare.state() },
  Effect.gen(function* () {
    const worker = yield* Worker;
    return { url: worker.url };
  }),
);

Key differences:

• entrypoint is now called main
• await is now yield*
• No more finalize() — the Stack handles lifecycle automatically

Step 2: Keep your async handler

Your existing Worker runtime code does not need to change. The async pattern declares bindings on the Worker’s env prop and uses Cloudflare.InferEnv to type the env object:

alchemy.run.ts

export type WorkerEnv = Cloudflare.InferEnv<typeof Worker>;

export const Worker = Cloudflare.Worker("Worker", {
  main: "./src/worker.ts",
  env: { Bucket },
});

Your handler stays the same — just update the type import:

src/worker.ts

import type { Env } from "../alchemy.run.ts";
import type { WorkerEnv } from "../alchemy.run.ts";

export default {
  async fetch(request: Request, env: Env) {
  async fetch(request: Request, env: WorkerEnv) {
    const object = await env.BUCKET.get("key");
    const object = await env.Bucket.get("key");
    return new Response(object?.body ?? null);
  },
};

Cloudflare.InferEnv derives a fully typed env object from the env declared on the Worker. You get type safety on the binding names and their APIs without using Effect in your runtime code.

Tip

This is the recommended migration path. Get your infrastructure on v2 first, then optionally adopt Effect for runtime code later.

Step 3: Deploy

The CLI commands are the same:

alchemy deploy
alchemy destroy

Your v1 state is not compatible with v2. On your first deploy, Alchemy creates new resources. You should destroy your v1 stack first, then deploy with v2.

(Optional) Adopt Effect for runtime code

When you’re ready, you can switch to Effect-native Workers. This gives you typed errors, composable retries, and Effect’s HttpServer integration.

Instead of declaring env bindings on the resource props, you bind resources in the Worker’s Init phase using yield*:

src/worker.ts

import * as Cloudflare from "alchemy/Cloudflare";
import * as Effect from "effect/Effect";
import { HttpServerRequest } from "effect/unstable/http/HttpServerRequest";
import * as HttpServerResponse from "effect/unstable/http/HttpServerResponse";
import { Bucket } from "./bucket.ts";

export default {
   async fetch(request: Request, env: WorkerEnv) {
     const object = await env.Bucket.get("key");
     return new Response(object?.body ?? null);
   },
};
export default Cloudflare.Worker("Worker",
   { main: import.meta.url },
   Effect.gen(function* () {
     const bucket = yield* Cloudflare.R2.ReadWriteBucket(Bucket);
 
     return {
       fetch: Effect.gen(function* () {
         const request = yield* HttpServerRequest;
         const key = request.url.split("/").pop()!;
         const object = yield* bucket.get(key);
         return object
           ? HttpServerResponse.text(yield* object.text())
           : HttpServerResponse.text("Not found", { status: 404 });
       }),
     };
   }),
);

The Worker resource declaration moves from alchemy.run.ts into the Worker file itself (using import.meta.url as the main), and the Stack just yield*-s the imported Worker:

alchemy.run.ts

import * as Alchemy from "alchemy";
import * as Cloudflare from "alchemy/Cloudflare";
import * as Effect from "effect/Effect";
import Worker from "./src/worker.ts";
import { Bucket } from "./src/bucket.ts";

export type WorkerEnv = Cloudflare.InferEnv<typeof Worker>;
 
export const Worker = Cloudflare.Worker("Worker", {
   main: "./src/worker.ts",
   env: { Bucket },
});

export default Alchemy.Stack(
  "MyApp",
  { providers: Cloudflare.providers(), state: Cloudflare.state() },
  Effect.gen(function* () {
    const bucket = yield* Bucket;
    const worker = yield* Worker;
    return { url: worker.url };
  }),
);

Summary

	v1 (async)	v2 (async style)	v2 (Effect style)
Stack	await alchemy("name")	Alchemy.Stack("name", ...)	Alchemy.Stack("name", ...)
Resources	await Bucket(...)	Cloudflare.R2.Bucket(...)	Cloudflare.R2.Bucket(...)
Worker entry	entrypoint	main	main: import.meta.url
Bindings	bindings: { KEY: resource }	env: { Key: resource }	yield* Binding(ref)
Runtime code	async fetch(req, env)	async fetch(req, env)	Effect.gen(function* () { ... })
Lifecycle	await app.finalize()	automatic	automatic
Type safety	runtime errors	typed env via InferEnv	full Effect type system

Where next

• Tutorial — build a full app on v2 from scratch, on Cloudflare or AWS
• Bindings — what replaced v1 bindings:
• Cloudflare — the Cloudflare provider hub
• AWS — the AWS provider hub