Posted September 21, 2021
From what I can see, the game received its most recent Steam patch on 12 August 2021. On GOG, there's an update on 20 August 2021, so it stands to reason that the game would be up-to-date here. That being said, the devs are known to have released GOG builds much more infrequently compared to Steam builds during Early Access and the fact that they use different build numbers on GOG and Steam makes it pretty hard to be certain about the current build without actually owning it on GOG.
Snowslinger: Does anyone know if Chernobylite is of the latest version? I see it is missing a DLC and I am a bit concerned about getting it on GOG, because the devs might not care about GOGers.
You might want to also post your question in the Chernobylite sub-forum, since people there probably own the game on GOG and can check whether functions mentioned in the latest patch notes on Steam are available in the current GOG build.
Compare https://steamdb.info/app/1016800/patchnotes/ and https://www.gogdb.org/product/1472128402#builds . Also, regarding the cosmetic White Rose DLC, there was some chatter about the DLC coming to GOG or even some people getting it for free, but I have no idea if that ever worked out.