Do i really have to buy it again just to get an up to date version?

It's in beta on steam. And I have to the best of my abilities actually made a beta branch here on GoG, but I think you need to access it manually through their galaxy. Beta can potentially be buggy, that's why players need to actively select it. The official version is released on steam and GoG simultaneously, a few weeks after beta trials.

Actually, it seems I have succeeded, here's a guide for galaxy:
https://support.gog.com/hc/en-us/articles/360003904358-How-can-I-access-beta-channels-?product=gog

Amazing! Thank you!

Not your problem I know, but that absolutely stinks! A main reason I buy from Gog is to avoid having to install another bloated store front application like Galaxy or even worse Steam.

The GOG reasoning for only having betas via Galaxy is complete BS.

They are without a joke, saying it is "too hard" to create offline installer for betas, what rubbish! Offline installers for beta are no more difficult than release versions. They should be downloadable with a BIG disclaimer that you are downloading a beta and do so at your own risk.

This is nothing but a way to force people to download Galaxy just to inflate the user numbers. Really poor from Gog.

I agree on the galaxy part. I'm not a big fan of any bloat what so ever. But for SoS development I must admit it's kind of nice to have these things, so that the version I intend are played by the player automatically, since I have a habit of doing two bug fix updates per day on occasion. (I don't like this either, BTW, personally hate updates, just make stuff that works and stop using customers as free testers, like in the good old days). But, it's also the only way I can make the game and add content in the pace I currently am. So it's a dilemma.