Chaos Physic performance is disasterous. Im not talking about % in comparasion against old PhysiX(referencing ue4.19), differences is about 3 times minimum up to immeasurable 30 times and over. Also im not talking about specific user case especialy advanced new features, also im not talking about bugs. Chaos is disastrous slower in basic fundamental funcionality. in addition to all the performance issues related to lumens and vsm, the chaos physics situation is somehow overlooked. but in fact the main bottleneck is chaos physics. if you’re developing a game where you don’t have a large number of physical actors at the same time, it somehow drags on, but if you want a multiplayer with 24 or more players, it’s simply impossible now. i tried to turn off within the project settings every possible advanced option related to physics and collissions, i also turned on async, and i managed to double the performance (also increassing bug probability) but still it’s at least 3 times worse on basic stuff compared to PhysicX. I assume that the epic in fortnite uses the locally optimized inhouse version, although there is a noticeable drop in performance after the upgrade. I’m afraid that epic won’t improve this situation in the near future, and I’m most afraid that their plan b is the assumption that over time, the hardware will overcome the current lack of performance with raw power. I hope I’m wrong, but I don’t see anything improving anytime soon, I’m talking about the next few years.
This is such a complex topic… As every dev has different project goals, different hardware specs and OS setups.
Its like trying to benchmark the engine out of the box, when default settings between UE4 & UE5 are so different.
Overall it’d be interesting to see a POLL about Chaos… How many users are sticking with UE4 to avoid it for now?
Plus, how many other devs have attempted to port PhysX over to UE5 maybe as some devs have apparently tried. 
admit it is very complex teme, and im talking about pure physix in 4.19 i guess, some version after 4.21 they start slowly to implement chaos and in every next version its getting slower and slower. and it is not exactly just physix engine but all other engine parts wich rely on physix and collisions. and remember ue4.21 realeased almost 6yrs ago so aint go back. to emphasize, im not bother with new and advanced stuff, simply put in ue4.19 in multiplayer game it is possible, for me, to have a scene with (simple empty test scene, nothing visual demanding) over 15 players in close field of view (say up to 30m) with <3ms tick time (stat game), that number in ue5.3 is 9ms and whatever i try, can’t get it down below 7ms. that means the casual shooter games, free for all, team detmatch and the alike (everything what unrealtournament was) is gone with wind, of course in fortnite its very rare case that you have 15 players in the field of view at 30m. this is all on ryzen 9 3900x and rtx3070. Not to be dramatic, it is really possible to make a whole range of games with exceptional visuals, which will easily push 60fps, but to make a game like unrealtournament with average visual demand, but to be able to push over 120fps in mass scenes is not possible, what irony.
to enable chaos in ue4 you have to build from source and it’s available since 4.26, default branch is using physx…
aint know for sure, but in 4.23 in project physix settings you have first chaos parametars. and since that version (4.23) i have constant degradation in performance in every new ue. i assume they not sudden replace physix, but start to rearange engine modules to make compatibile with chaos an all upcoming changes, so thats it.
I did spend about 2 weeks fine tuning all the constraints but am happy with Chaos and proud of the engineers at Epic. Here is a video of a 100% physics motorcycle and rider running at solid 60 FPS on PS4 and physics running at 120FPS:
I had to convert from 4.27Plus and was really dreading it because the game is heavy physics based and I had tested Chaos in 5.0 and it was slow and buggy. Now in 5.4 I had to upgrade and it went so much smoother than I thought. https://youtube.com/shorts/mrFF2TDatv4?si=lIbVMr2C9yclBMxN