you might be interested in what BI just posted on their website:
With update 1.40 just around the corner, a ‘Release Candidate‘ was made available over the weekend, which we’ve recently updated with miscellaneous maintenance and stability tweaks. These ‘RCs’ use a special ‘branch’ of data and exes, which helps our team to validate the stability of our updates ‘in the wild’, before they roll out to everyone. It also enables content creators to ensure the compatibility of their own custom creations with the latest version of Arma 3 ahead of time. If you’d like to participate in the final stages of testing, open the ‘BETAS’ tab of Arma 3’s Steam properties, and enter the access code Arma3Update140RC. Right now, we’re primarily focused upon validating some tweaks to MP stability. The update itself is set to bring several interesting Dev-Branch features to all Arma 3 players; let’s take a quick look at these now.
More in the full SITREP