For the duration of a major release, up until ~x.4 pretty much everything from upstream gets backported with a delay of 6-12 months, depending on how conservative to change the rhel engineer maintaining this part of the kernel is.
After ~x.4 things slow down and only "important" fixes get backported but no new features.
After ~x.7 or so different processes and approvals come into play and virtually nothing except high severity bugs or something that "important customer" needs will be backported.
