Google is telling those who used the Google Ads API to make sure to migrate the Feed-based extensions to supported Asset-based extensions soon. I believe the deadline will be October 20, 2021. Also, Google announced the new {extensionid} ValueTrack parameter will be available beginning June 24, 2021.

All existing Feed-based extensions will automatically migrate to Asset-based extensions in batches. Callout, Promotion, Sitelink and Structured Snippet extension types will automatically migrate on October 20, 2021 and then sunset on February 15, 2022. App, Call, Hotel Callout and Price extension types will automatically migrate on February 15, 2022 and then sunset on April 8, 2022. Asset-based Image extensions will not be available in the Google Ads API until 2022.

Google said that the new {extensionid} ValueTrack parameter will be available beginning June 24, 2021. You can use this parameter to track clicks on your Asset-based extensions. The {extensionid} parameter for Asset-based extensions mirrors the behavior of the existing {feeditemid} parameter for Feed-based extensions.

Forum discussion at Twitter.