How to get endless mode?

Unfortunately, we still didn't got the update who include it.
I tried to contact devs about this through their website twice, but never got an answer :/ That's a shame because I really like the game.

Well, this is tragic. I'll still be keeping an eye out for this, yet - until the GOG version has all of the content as the Steam version - we should probably mark Karate Survivor as officially outdated until further notice in the general GOG community hub, which has several lists of outdated GOG games.