I got the email this morning.
"Important changes to your Google AdSense ad units."
"We're investing heavily in understanding the best ways to increase user interest in ads and how our ads perform. As a result, our formats are constantly being updated and improved. You may have noticed these new types of ads showing up on your sites."
"We’re committed to continuously investing in the modernization of our advertising products. As a result, there are some important changes we're making to some AdSense features that you have used or configured in the past. Your Ads tab will be updated in the coming weeks to reflect the following changes:
1. Ad sizes
We've made it easier to create and manage ad units. All ad units will be created Responsive by default to adjust to different screen sizes on mobile and desktop for increased performance and flexibility. If you do need further customization, you’ll still be able to create custom sized ad units.
2. Ad types
We’re moving towards richer ad formats, phasing out text-only and display-only ad units to further improve user experience, and to fully reflect the pool of ads we have in the market. As a result, the "Text ads only" and "Display ads only" ad units in your account have been renamed to “Display ads” and from early 2019 will be updated to serve all ad types.
3. Text ad styles
We’re deprecating text ad styles for "Text & display ads" ad units. From now on, you won’t be able to create ad styles for your new ad units. Your new ad units will have Google-optimized text ad styling. As this feature is being deprecated, your existing ad styles will also be optimized by Google in the following months. For customization and improved user experience, you can use native ads on your site.
4. Simplifying “If no ads available”
We’re continuously working to increase the quality and safety of our ad network and reduce the number of malicious ads that enter the AdSense network. As a result, we're removing the “If no ads available” option and we’ll be defaulting to collapsing the ad space or showing a blank space instead. If your current setting is a color or another URL, it will be updated in the near future your current settings will stop serving in the near future.
As a result of the above changes, we're also removing obsolete ad unit setting experiments. Any active ad unit experiments will stop in the following weeks. In conjunction with this, we are removing the experiments report from the Reports tab. For remaining experiment types, aggregate metrics will still be available in the experiment details page.
6. Synchronous code
Changing your ad code type to synchronous in your AdSense account won’t be available anymore. If you do need synchronous ad code, you can still manually update your ad code using this guide.
To tell us what you think, visit the Ad units page and click the Feedback button in the main navigation bar. We’re looking forward to receiving your feedback!"
(Numbering, Spacing, Bolding and Increased font sizes added by me, for clarity.)