At CloudFlare we've not explicitly treated traffic from Tor any differently, however users of the Tor browser have been more likely to have their browsing experience interrupted by CAPTCHAs or other restrictions. This is because, like all IP addresses that connect to our network, we check the requests that they make and assign a threat score to the IP. Unfortunately, since such a high percentage of requests that are coming from the Tor network are malicious, the IPs of the Tor exit nodes often have a very high threat score.
With most browsers, we can use the reputation of the browser from other requests it’s made across our network to override the bad reputation of the IP address connecting to our network. For instance, if you visit a coffee shop that is only used by hackers, the IP of the coffee shop's WiFi may have a bad reputation. But, if we've seen your browser behave elsewhere on the Internet acting like a regular web surfer and not a hacker, then we can use your browser’s good reputation to override the bad reputation of the hacker coffee shop's IP.
The design of the Tor browser intentionally makes building a reputation for an individual browser very difficult. And that's a good thing. The promise of Tor is anonymity. Tracking a browser's behavior across requests would sacrifice that anonymity. So, while we could probably do things using super cookies or other techniques to try to get around Tor's anonymity protections, we think that would be creepy and choose not to because we believe that anonymity online is important. Unfortunately, that then means all we can rely on when a request connects to our network is the reputation of the IP and the contents of the request itself.