r26 is the new LTS release. The support window for r25 has now ended. NDK r26 will remain in support until this time next year or the next LTS release, whichever comes later.
The main highlight is that this release includes an updated LLVM and libc++. We're reworked things so our libc++ comes from the rest of our LLVM distribution, so all future LLVM updates will also include libc++ updates.
r26 will be the first release that does not support KitKat (API levels 19 and 20).
See
the changelog for changes and announcements.