The Workers' date
The compatibility date every Worker on cf runs at: the build date of the workerd that cf
installs, through miniflare. workerd's version carries it, as in 1.20261012.1. It's the newest
date the local runtime knows, so dev and tests run what production does, and it moves only
when pnpm align moves cf.
From 2026-08-04, the date turns on Node.js compatibility, so no Worker sets a flag for it.
import { createRequire } from "node:module";
const fromCf = createRequire(createRequire(import.meta.url).resolve("cf/package.json"));
const fromMiniflare = createRequire(fromCf.resolve("miniflare/package.json"));
const workerd = fromMiniflare("workerd/package.json") as { version: string };
const built = /^\d+\.(\d{4})(\d{2})(\d{2})\./.exec(workerd.version);
if (!built) throw new Error(`workerd ${workerd.version} doesn't carry a date`);
export const COMPATIBILITY_DATE = `${built[1]}-${built[2]}-${built[3]}`;