But also everyone sane avoids the built-in http client in any production setting because it has rather severe footguns and complicated (and limited) ability to control it. It can't be fixed in-place due to its API design... and there is no replacement at this point. The closest we got was adding some support for using a Context, with a rather obtuse API (which is now part of the footgunnery).

There's also a v2 of the json package because v1 is similarly full of footguns and lack of reasonable control. The list of quirks to maintain in v2's backport of v1's API in https://github.com/golang/go/issues/71497 (or a smaller overview here: https://go.dev/blog/jsonv2-exp) is quite large and generally very surprising to people. The good news here is that it actually is possible to upgrade v1 "in place" and share the code.

There's a rather large list of such things. And that's in a language that has been doing a relatively good job. In some languages you end up with Perl/Raku or Python 2/3 "it's nearly a different language and the ecosystem is split for many years" outcomes, but Go is nowhere near that.

Because this stuff is in the stdlib, it has taken several years to even discuss a concrete upgrade. For stuff that isn't, ecosystems generally shift rather quickly when a clearly-better library appears, in part because it's a (relatively) level playing field.