According to the FAQ[1], they also offer 9.9.9.10, which passes client subnet at the cost of other features.
It appears 1.1.1.1 also does not pass client-subnet, atleast not by default. Queries to my authoritative from Google always includes client subnet, OpenDNS required request for whitelist. For Cloudflare its unclear.
Wow, this is actually a huge issue. Just as a simple test, I tried nslookup google.com for both 1.1.1.1 and 8.8.8.8, and Cloudflare's responses ping at about 200ms, whereas Google's responses ping at ~10ms.
dig @8.8.8.8 o-o.myaddr.test.l.google.com txt +short
"74.125.46.11"
"edns0-client-subnet 94.181.44.185/32"
dig @9.9.9.10 o-o.myaddr.test.l.google.com txt +short
"2620:171:57::240"