Hi,
I've decided to start doing some of the cleanup changes that will break ABI and/or API (which has been stable since nettle-3.6, released 5 years ago). I think the more interesting planned changes are listed on https://git.lysator.liu.se/nettle/nettle/-/issues, and the most disruptive one is dropping the length argument for the various _digest functions (https://git.lysator.liu.se/nettle/nettle/-/issues/5). Changes will be released as nettle-4.0. Focus will be on changes affecting libnettle, to be able to get this done in a reasonable time, but it will nevertheless imply an soname bump also for libhogweed.
If needed, bug fixes will be back-ported to a compatible nettle-3 branch, for additional 3.10.x releases.
If you have opinions on what breaking changes should or shouldn't be done at this time, this is a good time to speak up. If that is helpful for applications to transition, I'm open to add some preprocessor defines or headers that can be used to get API (but not ABI) compatibility with nettle 3.
Regards, /Niels