Nipoti: Not even the galaxy version is updated. Anyway, the game is always updatable through the luncher if this delays persist.
rkralik: I looked for this last night in the ToME launcher and couldn't find how to update the game engine, only the add-ons. Can you explain how to force it?
Currently the DLCs and the core-game sold by GOG as being no-internet-connection-required are at version 1.5.3 (and also currently discounted in the Summer Sale).
If you temporarily want to lose the no-internet-connection-required feature in return for having access to version 1.5.5 right now, then you do have the option of downloading the open-source release from the developer's website direct. [1]
[1]
https://te4.org/download Here is the developer's statement in their FAQ: "Does it matter where I buy the game? No it does not, … If you buy the game on GOG you can get it on te4.org" [2]
[2]
https://te4.org/tome/faq My understanding is that the only difference between GOG's version and the developer's binaries is that GOG's is being sold with the guarantee of "No activation or online connection required to play." and is modified to be compatible with this guarantee. If neither of these features are important to you, then the developer is currently providing open-source access to the 1.5.5 release where paid features and paid DLCs are accessible when activated online and played with an online connection.