Ginny Marvin, the Google Ads Liaison, said the Google Ads team has updated its additional best practices for Performance Max help document with more details on how final URL expansion works in this context. This was supposedly added within the past few weeks.

Ginny added these additions were added mostly based on questions asked on social – so clarify any of those questions.

Here is what was added:

• If you create a Performance Max campaign for online sales goals with a Google Merchant Center product feed, we strongly recommend that you include additional creative assets in order to help drive the best performance. If creative assets are not provided, in some cases, we may help auto-generate the following assets on your behalf:
• Videos are auto-generated based on the provided text and image assets.
• If you turn on the final URL expansion feature, headlines and descriptions may be auto-generated for Search text ads based on the provided final URL. This is not available to campaigns with exclusively store goals.
• Headlines and descriptions are auto-generated based on the provided final URL. This is not available to campaigns with exclusively store goals.

Here is the confirmation tweet from Google:

Yes, we’ve added more about how final URL expansion works in this context, largely as a result of the questions asked here, so thank you.

We’ll continue to update & add clarifications to Help Center pages, particularly as Performance Max evolves.

— AdsLiaison (@adsliaison) May 3, 2022

Forum discussion at Twitter.