"pg_upgrade does its best to make sure the old and new clusters are binary-compatible, e.g., by checking for compatible compile-time settings, including 32/64-bit binaries. It is important that any external modules are also binary compatible, though this cannot be checked by pg_upgrade."

This makes me very nervous tho, I've at least two exts (trigrams and gists) maybe they work, maybe not, I just prefer the ease of mind of a old fashioned dump.