The Tor Project are currently using Fastly as the default for domain fronting in their Snowflake plugin, with cdn.sstatic.net (which serves various assets for Stack Exchange sites) as the front host, and snowflake-broker.torproject.net.global.prod.fastly.net as the target host.

Prior to this, they were fronting via Azure, using ajax.aspnetcdn.com as the front for target snowflake-broker.azureedge.net. But they switched to Fastly after Microsoft announced they'd be changing their policy to explicitly block domain fronting: https://www.microsoft.com/security/blog/2021/03/26/securing-...