Error importing `cloudflare:workers`

I am trying to use a Cloudflare Durable Object in development. This requires

import { DurableObject } from "cloudflare:workers";

import { DurableObject } from "cloudflare:workers";

import { DurableObject } from "cloudflare:workers";

import { DurableObject } from "cloudflare:workers";, which fails with the following error:

Error: Cannot find module 'cloudflare:workers' imported from '<path/to/sourcefile>`

Error: Cannot find module 'cloudflare:workers' imported from '<path/to/sourcefile>`

Error: Cannot find module 'cloudflare:workers' imported from '<path/to/sourcefile>`

Error: Cannot find module 'cloudflare:workers' imported from '<path/to/sourcefile>`