When they updated CI 3.x ?

There is no formal release schedule for either CI3 or CI4. Insitefx's answer is actually bang on.

The develop branch of CI3 has had a number of fixes applied, and some enhancements. The next release could be 3.1.11 or 3.2.0, depending on how much is chosen to be bundled with it. That decision, and the timeframe, is up to the repo/version maintainer.

The develop branch of CI4 has had a number of fixes and enhancements as well. The next release is *expected* (but not guaranteed) to be 4.0.0-rc1, but we are making extra sure that we have it as right as we can before launch.

CI3 will continue to be supported for some time (2 years??), even after the release of CI4.
CI3 is not disappearing.

Given that CI development is volunteer community-driven, there is no firm release schedule (eg every X months).