The game released on GOG on January 30, 2018, but the Steam News page for the game shows 4 updates from March 5 through April 4, 2018... some had new puzzles, others were fixes, etc. From the looks of it (unless Zachtronics never updated the version number and never added patch notes to GOG) it's still the original release from January 30.

Anyone know?

Spoke to Zach via email... he said he's going to get the GOG version updated next week to be inline with the Steam version.

Interesting that everyone complained about the absence of this game, and then no one even noticed that the game wasn't updated for many months.

He's already sent the files to GOG, most likely this week it'll be updated.

And how do you know that it was updated, if it is not? (I mean, I don't even have steam account, nor am I tracking every developer on twitter and I didn't install the game yet, so as long as there was no update on GOG, there's no chance to know about it... except buying a better crystal ball).

Now the download seems updated, changelog is missing.