@Krzysztof.N
So as of 5.4 DX11 SM5 SWRT Lumen GI worked perfectly … the use case is to be able to spin up thousands of instances on pixel streaming without huge aws GPU G5 cost and allow multiple sessions per instance. Its also the last hidden gem to squeeze an “optimal” quality rendering yet still hit really responsive frames where it feels like the majority of ppl maybe didn’t know this optimization path even existed [WELL WE DID AND WE TOOK ADVANTAGE 
] (you asked what the benefit was) Our workflow entails traditional LOD groups, non nanite DX11 SM5 with lumen SWRT GI and we maintain 90FPS or higher with 4 sessions shared on average on very low spec AWS instances in our fleet. Not needing to worry about nanite software rasterization, WPO limitations, SM6 memory footprint, HWRT GPU instances or due to being a chunk loaded application not needing to worry about nanite mesh sizes made this a win, win, win all the way around.
We also have DX11 SM5 Lumen projects running on APUs and Steamdeck and it was a hidden gem for GI and awesome performance for older gen hardware (GTX cards even) I go over a quick profile between 5.4 DX11 with lumen and DX12 (SM6) as required in 5.5 and its over a 20 frame loss in performance at native res and default settings on both (On a RTX 2080ti) the falloff is far greater on lower RTX cards like the RTX 2060. I honestly think marketing and awareness could have been better here instead of ppl focusing on the heavy lift of DX12 and SM6 … communication could have been to fall back to DX11 and SM5 to get some of that performance back. Outside of the little bit of extra chaos thread cost it was pretty close to UE4.27 perf not including the lumen gathering cost which wasn’t bad at all if you used global vs detail. TSR or FSR also working here was icing on the cake to push very very low end cards over the 60fps mark. Trust me it works!
I go into much better detail in this post between each model and rhi.
Summary: Its about a total loss of 123% of the initial starting 4.26ms on a RTX 2080ti if we look at UE5.5 alone going from dx11 sm5 to lumen and 110% loss of performance in something that ran well over 120fps in 5.4 with lumen SWRT enabled.
Lumen no longer working in UE5.5 DX11 SM5 - Development / Rendering - Epic Developer Community Forums
Also a little constructive feedback… As well as a plea to please reconsider this decision? This is going to literally block us from moving past UE5.4 unless we want to take on the massive task of pulling support forward ourselves in 5.5 source (which we likely won’t). A change like this that isn’t “announced”, included in patch notes or have some official documentation other than ppl digging through forums is a little rough to swallow. Please don’t take that the wrong way … I’m just asking for a bit of empathy. No different than I know that maintaining multiple renderers across desktop and mobile is a huge burden… and one we are extremely grateful that you guys are wrangling. Just like … A little better heads up would be awesome especially when the official release notes and docs still seems to make you believe SM5 Lumen is still supported.
