Almost no sites disabled Dynamic Page Cache! 135475 using it, 138764 using Page Cache (so 97.6% of sites using Page Cache also use Dynamic Page Cache).
Dynamic Page Cache
Only 72735 of the total of 153104 measured sites use Standard — or 47.5%. Minimal is on 1464 — or 0.9%. That means over 50% is using a contrib/custom install profile!
rest is used on 18878 or 12.33% of D8 sites. serialization is on 21724 or 14.18% and hal on 11541 or 7.54%.
API first initiative
Basic Auth is used on 7962 or 5.2% of D8 sites. That means 42% of sites using REST use Basic Auth for authentication REST requests. The remainder must be using cookie/anonymous authentication, or contrib auth modules like simple Oauth or JWT