AWS pushed out the docs for this new feature but then quickly pulled them down. Likely it will be announced during re:invent coming up.
The original doc url (taken down now) was: https://docs.aws.amazon.com/lambda/latest/dg/invocation-urls.html
Google has a cache here: https://webcache.googleusercontent.com/search?q=cache:Qr4xUaiHjAsJ:https://docs.aws.amazon.com/lambda/latest/dg/invocation-urls.html+&cd=1&hl=en&ct=clnk&gl=us
Very exciting as I just spent a few hours cobbling together the cloudformation for a simple API gateway -> Node lambda. The lambda just calls a few AWS APIs. Cutting out the API gateway will be a plus.