Windows 11 update 'KB5066835' reduces performance of some games by up to 50%
It has been reported that in environments where the update 'KB5066835' released in October 2025 for Windows 11 24H2 and 25H2 has been applied, there is an issue that significantly reduces the performance of certain game titles.
Proof That Recent Windows Update Harms Gaming Performance | Digital Foundry
Windows 11 KB5066835 Update Triggers Major Gaming Performance Regression
'KB5066835' is one of the updates distributed in the October 2025 Windows Update , and fixes issues such as 'an issue that caused the print preview screen to stop responding in Chromium-based browsers.'
October 14, 2025—KB5066835 (OS Builds 26200.6899 and 26100.6899) - Microsoft Support
https://support.microsoft.com/ja-jp/topic/2025-%E5%B9%B4-10-%E6%9C%88-14-%E6%97%A5-kb5066835-os-%E3%83%93%E3%83%AB%E3%83%89-26200-6899-%E3%81%8A%E3%82%88%E3%81%B3-26100-6899-1db237d8-9f3b-4218-9515-3e0a32729685
However, this update has had another negative effect: it has caused a performance degradation in games. According to the gaming news site Digital Foundry, one of the games that has been confirmed to have a performance degradation is Assassin's Creed: Shadows.
Amazon.co.jp: Assassin's Creed Shadows Limited Edition (Amazon Exclusive) PlayStation 5: PC Software
Digital Foundry measured the performance difference between with and without the NVIDIA patch on a PC equipped with a Ryzen 7 9800X3D processor and an NVIDIA RTX 5090 GPU, and found that without the patch applied (i.e., with the effects of KB5068835), frame rates dropped by 33% to 50% when playing Assassin's Creed: Shadows.
Additionally, users have pointed out that Counter-Strike 2 will also be significantly affected.
🚨 CS2 FPS BOOST - 11% increase in 1% Lows for me after installing the NVIDIA Hotfix Driver 581.94 🚨
— Thour (@ThourCS2) November 20, 2025
📊 Avg. FPS, 1% Lows:
581.29: 780.4 FPS, 297.1
581.94: 794.5 FPS, 331.6 (11.61%🔼)
1280x960, Reflex Enabled, MSAA 4x, Dust2 FPS Map.
9800X3D, RTX 5070, Windows 11 25H2 https://t.co/7u9QDvPqgW pic.twitter.com/yXRYcNO1AD
In response to this situation, NVIDIA has provided a specific patch, saying, 'KB5068835 has been updated to address the issue of reduced performance in some games.'
GeForce Hotfix Display Driver version 581.94 | NVIDIA
https://nvidia.custhelp.com/app/answers/detail/a_id/5750/~/geforce-hotfix-display-driver-version-581.94
However, the negative impact of KB5066835 does not only occur with NVIDIA GPUs, but has also been confirmed with AMD Radeon and Intel Arc Graphics. According to Windows Latest, all systems running Windows 11 25H2 Build 26200.6899 or later or 24H2 Build 26100.6899 or later may be affected.
Nvidia confirms gamers could experience degraded performance in some games after applying the Windows 11 October 2025 Update.
— Windows Latest (@WindowsLatest) November 20, 2025
October 2025 Update is a mandatory security patch for Windows 11 25H2 / 24H2, and it cannot be skipped.
It's unclear if non-Nvidia PCs are also having… pic.twitter.com/YHdwWac5W4
As a result, users using GPUs other than NVIDIA will likely have to wait for Microsoft to respond.
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