Sebastian Larranaga

I can confirm, the issue persists for me on Windows. GPU usage on 1.21.10 averages between 90-100% even in non-intensive environments, with an FPS reduction of 30FPS when compared to GPU usage on 1.21.4 ranging between 60-80% on 1.21.4 while providing a steady 144 fps with the same settings across both versions. I’ve given up hope that the issue will ever be resolved, as the last true update we got was from July saying it was a big refactor that did not fit into a previous release. It appears this issue’s been swept under the rug by Mojang and it seems very unlikely they will revert to the old rendering methods prior to 1.21.5, so unfortunately I’ve just decided to stop playing Minecraft altogether. Hopefully they’re able to eventually fix it for you guys!

Hey reporting back and just like Liv, the only reason I made a Mojira account was to vote on this issue. The issue itself for me is that using any shaders from Iris in my use-case alongside performance mods that would catapult me over 170fps easily in 1.21.4 has seen a massive regression in performance after 1.21.5 and even on 1.21.8 – now with those same mods and shaders, I’m lucky to be getting my FPS in the low 89 - 103 range.

According to the Iris devs, it has to do with Minecraft Java’s rendering pipeline being completely re-worked (probably due to vibrant visuals prep, but again, I’m definitely not an expert on the topic so please correct me if I’m wrong). Is this something Mojang devs and engineers are actively trying to fix and can we expect this significant drop in FPS to be an issue that’s addressed and fixed in 1.21.9?

I’m playing on PC using an Intel Core i7 13700k, an RTX 4070 and 32GB DDR5 RAM (8GB allocated to Minecraft) and this regression in performance has also been impacting me as well. It started during 1.21.5 (it doesn’t happen in 1.21.4) but every version subsequent to 1.21.5, snapshots included, all the way up until the latest release as of July 19th, 2025 (1.21.8) have been significantly laggier, slower and sluggish especially when using shaders (my GPU usage stays between 93% and 100%).

I tested some stuff out with some controlled variables. I should mention I used the exact same mods and shaders I used on 1.21.4 for 1.21.5, 1.21.6, 1.21.7, and 1.21.8. Even when I’m not using shaders, my GPU usage is hovering anywhere from 70% to 90% on vanilla Minecraft with no mods and no shaders on 1.21.5 and above.

Using the same seed and teleporting to the same precise coordinates in that world, I’m obtaining approximately 150fps at the highest shader settings on Minecraft with mods in 1.21.4 (render distance set to 16 chunks, simulation distance set to 12 chunks and shadow distance set to 8). With all variables maintained exactly the same except for version of Minecraft, I tried the same thing on all versions including and after 1.21.5. I observed a drop in performance that ranged anywhere from 26% to 40% using the same settings, mods, shaders, etc.

I hope this helps the devs and engineers resolve the issue. I’m using the latest NVDIA drivers as of July 19th, 2025 and the latest version of Windows 11.