What's the appropriate typescript type (within Env) for a binding to another worker?

For instance, for a durable object it would be:

interface Env {
  MY_DO: DurableObjectNamespace
  MY_WORKER: ???
}

interface Env {
  MY_DO: DurableObjectNamespace
  MY_WORKER: ???
}

interface Env {
  MY_DO: DurableObjectNamespace
  MY_WORKER: ???
}

interface Env {
  MY_DO: DurableObjectNamespace
  MY_WORKER: ???
}

Guessing it could just be a fetch handler, but would be nice to know what TS type is expected specifically