The latest version available is 4.1 (this is the latest "unstable" branch) - the latest stable branch is 4.0. 4.2 isn't released yet, but when it is, it will simply be a "stable" version of the current 4.1 branch (in tvheadend world, even numbers, i.e. 4.0, 4.2 are classed as "stable" releases whilst odd numbers, e.g. 4.1 are classed as "unstable" (or development) versions).
If you want the latest version then you need to enable the "unstable" repository in your package manager (see "here"
I'm running the latest 4.1 builds and have no problems at all, and would recommend anybody on 4.0 upgrade to 4.1 as there are many enhancements in 4.1 over 4.0 which are worth having.
Be sure to backup your config before attempting to upgrade from 4.0 to 4.1 just in case anything goes wrong.