Today, Stadia has launched for iOS devices via the Safaria browser. The news comes from an official Twitter post:
Relatedly, GeForce Now is also supported on iOS devices.
Apple has been silent so far on cloud gaming services circumventing their Apple Store policies. They have said, though, that they cannot offer cloud gaming apps because Apple would need to vet every game playable via the service. Apple may take action to block the streaming services from Safari in the near future, but we’ll keep you updated.