Croteam sure are busy, not only did they confirm The Talos Principle 2 is happening, but it seems I missed the fact that Serious Sam 4 was also confirmed to be in development right now.
Can't make it any clearer than what they said in the below tweet:
I should really go back and finish Serious Sam 3 sometime soon, as it was a pretty fun shooter. I never did get very far in it though, due to so many other things happening around that time.
Like with Talos 2, details are light right now as the announcement was made at the Nordic Game event.
Croteam really are awesome. They were one of the first developers to support Linux when Steam arrived, so I look forward to seeing what they can do with their future games on Linux.
It's exciting, as it's likely it will also use Vulkan since their engine now supports it.
Cheers for pointing it out Swiftpaw!