Google said they are rolling out AMP in the core mobile results, as they said they would back in August. We saw it pretty early on Monday, as did some others.
John Mueller of Google shared that this is a gradual rollout and not everyone will see it fully yet. It may take time he said:
Malte Ubl from Google, the lead tech on AMP, reiterated there is no ranking boost for going AMP specifically:
As announced before, this is not a ranking change. We simply link to AMP if there is such a version of a given doc.— Malte Ubl (@cramforce) September 20, 2016
Here is a GIF of the experience:
Again, you can only experience this on Google mobile search.