You no longer have to manually start Gemini summaries for long email chains, but you can also opt out if you don't want them.

When Gemini launched in the side panel of Gmail last year, one of the features allowed users to summarize their long email threads, along with other tools like those to draft email messages or see suggested responses,

Ever since Google started integrating its Gemini AI into all its apps, users have complained about seeing the optional AI-powered Summarize button in their Gmail threads. Now, Google is so confident about this feature that it’s enabling automatic summaries for all paying Google Workspace accounts with Gemini access.