It seems like it rebuilds itself with PGO. I can't tell if I'm being paranoid/didn't only include stdlib in something, but I ran some random programs, restarted my computer and the install is now at 320mb, vs. 213 when I first untarred it.
> PGO in Go applies to the entire program. All packages are rebuilt to consider potential profile-guided optimizations, including standard library packages.
Go1.21 uses PGO by default, if the file default.pgo exists.
> The -pgo build flag now defaults to -pgo=auto, and the restriction of specifying a single main package on the command line is now removed. If a file named default.pgo is present in the main package's directory, the go command will use it to enable profile-guided optimization for building the corresponding program.
https://go.dev/doc/pgo
> PGO in Go applies to the entire program. All packages are rebuilt to consider potential profile-guided optimizations, including standard library packages.