7.4 has passed QA and has been promoted to the Staging branch on Steam. While there still may be a few bugs to work out, if you want to try out the new vehicles a bit early, feel free to do so.
To clarify how our development process works:
[bleeding_edge_staging] -> untested, but the most current version of the game. Expect bugs and frequent new versions.
[staging] -> These builds have passed internal QA, but may still have a few issues.
[release] -> These are the official releases.
In general, we aim for 2-week release windows.