As always information is available on the OpenBSD site. The release notes go over all the changes, but the biggest change that caught my eye was this one:
There has been long talk about moving away from GCC on OpenBSD, but many of the older platforms were ‘trapped’ on GCC as they only have support for the CPU in older releases. And they have long since said it was difficult in submitting patches up stream and dealing with regressions. Sadly for GCC this has been an industry thing with even Apple moving away from GCC based compilers to CLANG.
Maybe it’s just inevitable, things change.
At least the Clang competition is driving progress from GCC too, so at least current and new platforms benefit from the competition. Also VMM is getting stronger, I should try it some day….