The team behind Godot Engine continue to push what an open source game engine can do, with a recent big release now behind them work continues towards another with some impressive changes.
It's going through a big code refactoring process right now, as written up in a blog post by Lead Developer Juan Linietsky. They said that while a lot of "core code changes" happened for the 3.0 release two years ago, they now have the chance to do even more for the massive Godot 4.0 release which will have Vulkan API support.
One major change is a "design flaw in Godot 3.0", that meant you couldn't always tell if an object instance was freed or not which created bugs that Linietsky said couldn't be fixed. Not a problem in the 4.x code branch, which can improve "performance considerably" and they may backport it to the 3.x releases.
Multiple other big changes were done, many of which will help improve performance. Including a removal of "PoolArrays (PoolVector in C++), replaced by PackedArrays" which was done for 32bit, since they no longer need it the replacement "improves performance in all operations related to large memory allocations".
Another big one is threaded resource loading, using a new API that's simpler and it can take advantage of many cores resulting in "4x to 6x performance increases, and in considerably improves the usability for background loading".
As for what comes next, during March they will continue the code refactoring and back to Vulkan API work in April. One of their upcoming goals is to "perform the separation of OS class into OS and DisplayServer", to allow them to support multiple windows, Wayland and Linux+EGL plus more API cleanups.
It really does sound like Godot Engine 4.0 due late this year is going to be an absolutely massive improvement for this cross-platform free and open source game engine.
See more about the FOSS game engine Godot Engine of the official site.