Irssi 1.5 is still under development. It is far away from release, but you can test the version in git.
I may erratically post some news here.
Notices to channels have become their own level, similar to MSGS vs PUBLICS there is now NOTICES and PUBNOTICES for your activity and ignore rules
Autotools was removed. Irssi can be built with Meson.
Some cruft was removed from the code, true colour is now always built, socks is removed, regex.h is removed.
IRC module is now optional, you can launch Irssi without IRC. It’s expected to find bugs in this regard! Also a good topic if someone wants to contribute (for example: move useful commands from IRC => common)
Github actions builds a termux package
Improve split window and layout switching and restoration, fix split window bug (window collapsing)
Support dynamic expandos
Coherent line meta-data architecture
Removal and replacement of /recode
??? your ideas ???
Also see the unofficial Roadmap