Not direct access, yet (they're not sufficiently programmable and isolatable). But as mikecb alludes to, we have a number of services like Translate, Vision, Speech, and a few others in Alpha that may be trained using TPUs (see https://cloud.google.com/ml for more).

For models you write yourself and have the Cloud ML service train, they will use our regular VMs today and as this blog post says, GCE will soon have GPUs (and therefore, Cloud ML will expose them, too).

Disclsoure: I work on Google Cloud (and sorry for the confusion!)

If you use the cloud ml service.