As of today incoming request data includes an extra bit of information on the X-analytics header. 

If an incoming request to any wikipedia project had no cookies whatsoever it will be tagged with nocookie=1. A requests without any cookies could correspond to a fresh browser session, a user browsing with cookies disabled or, most likely, a bot request as most bots will not accept cookies. We *might* be able to use this setting as a cheap proxy to quantify bot traffic.

Documentation about this change can be found here: 

Thanks, 

Nuria