As you know, Google began crawling some sites over HTTP/2 this month. While you can opt out of this, i.e. GoogleBot crawling your site over HTTP/2, you cannot opt in to it, at least not now.
John Mueller of Google said on Twitter "we don't manually pick sites for trials like that, it's more about whether it's possible & makes sense for crawling."
He also added that there is no ranking boost for being crawled over HTTP/2 - but we knew that.
Here are those tweets:
AFAIK we don't manually pick sites for trials like that, it's more about whether it's possible & makes sense for crawling. There's no ranking advantage.
— 🍌 John 🍌 (@JohnMu) November 19, 2020
In the short term, if you do not want Google crawling your site over HTTP/2, here is how to opt out. To opt out from crawling over HTTP/2, instruct the server that's hosting your site to respond with a 421 HTTP status code when Googlebot attempts to crawl your site over HTTP/2. If that's not feasible, you can send a message to the Googlebot team (however this solution is temporary).
And no, you cannot use that form to opt in.
Forum discussion at Twitter.
