The release notes for 1.16.3 say :
"important security fixes
bug fixes, memory leak fixes and various stability and reliability improvements"
They also say this is likely to be the last release in the 1.16.x series.
But it's not clear what those fixes are, specifically (none are identified explicitly as security issues). There also doesn't appear to be a reference to any srt fixes (see https://bugs.gentoo.org/761547#c1).