I'm not really sure - maybe Max knows? I know we vary on an `optin` cookie - maybe that will provide some clues?
Christian's response (below) tells us the "mf-m" key in the X-Analytics header has the information we need here. So we're all set. "a" means alpha site and "b" means beta.
[From Christian]:
For X-Analytics stuff,
would be the go-to place. I guess you're after the “mf-m” key there. That key is not set in varnish, but is set in the backend (MobileFrontendExtension), and it is still getting logged. But I am not aware of any reports still using that key.
Thanks Christian, sorry I didn't read the obvious documentation before dumping vague memories for awesome volunteers to help with.