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[Workers] update workers startup limits #25748

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Oct 10, 2025
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[Workers] update workers startup limits #25748

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[Workers] update workers startup limits
taylorlee Oct 10, 2025
3ae455a
Add changelog entry for increased startup time
mikenomitch Oct 10, 2025
9da5284
Update changelog for worker startup time increase
mikenomitch Oct 10, 2025
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15 changes: 15 additions & 0 deletions src/content/changelog/workers/2025-10-10-increased-startup-time.mdx
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---
title: Worker startup time increased to 1 second.
description: Worker startup time has been increased from 400 ms to 1s.
products:
- workers
date: 2025-10-10
---

import { Render, TypeScriptExample, WranglerConfig } from "~/components";

You can now upload a Worker that takes up 1 second to parse and execute its global scope. Previously, startup time was limited to 400 ms.

This allows you to run Workers that import more complex packages and execute more code prior to requests being handled.

For more information, see the documentation on [Workers startup limits](/workers/platform/limits/#worker-startup-time).
4 changes: 2 additions & 2 deletions src/content/docs/workers/platform/limits.mdx
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Expand Up @@ -18,7 +18,7 @@ import { Render, WranglerConfig, DashButton } from "~/components";
| [Environment variables](#environment-variables) | 64/Worker | 128/Worker |
| [Environment variable<br/>size](#environment-variables) | 5 KB | 5 KB |
| [Worker size](#worker-size) | 3 MB | 10 MB |
| [Worker startup time](#worker-startup-time) | 400 ms | 400 ms |
| [Worker startup time](#worker-startup-time) | 1 second | 1 second |
| [Number of Workers](#number-of-workers)<sup>1</sup> | 100 | 500 |
| Number of [Cron Triggers](/workers/configuration/cron-triggers/)<br/>per account | 5 | 250 |
| Number of [Static Asset](#static-assets) files per Worker version | 20,000 | 100,000 |
Expand Down Expand Up @@ -335,7 +335,7 @@ To reduce the upload size of a Worker, consider some of the following strategies

## Worker startup time

A Worker must be able to be parsed and execute its global scope (top-level code outside of any handlers) within 400 ms. Worker size can impact startup because there is more code to parse and evaluate. Avoiding expensive code in the global scope can keep startup efficient as well.
A Worker must be able to be parsed and execute its global scope (top-level code outside of any handlers) within 1 second. Worker size can impact startup because there is more code to parse and evaluate. Avoiding expensive code in the global scope can keep startup efficient as well.

You can measure your Worker's startup time by deploying it to Cloudflare using [Wrangler](/workers/wrangler/). When you run `npx wrangler@latest deploy` or `npx wrangler@latest versions upload`, Wrangler will output the startup time of your Worker in the command-line output, using the `startup_time_ms` field in the [Workers Script API](/api/resources/workers/subresources/scripts/methods/update/) or [Workers Versions API](/api/resources/workers/subresources/scripts/subresources/versions/methods/create/).

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