Forum Discussion
Vinne73
Sep 25, 2018Cirrus
https://groups.google.com/a/chromium.org/forum/!topic/blink-dev/IT3pYF5B_p4 - they say "In future releases we are introducing the “Purpose: prefetch” header to allow web servers distinguish prefetch traffic from user-initiated page load traffic."
So that confirms they were about to introduce the header.