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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →Windows 11 KB5066835 caused a serious gaming-performance regression on some systems, particularly in certain games running on NVIDIA GeForce hardware. Released on October 14, 2025 for Windows 11 24H2 and 25H2, the update was followed by reports of sharply lower FPS. NVIDIA later acknowledged the problem and released GeForce Hotfix Driver 581.94.
Windows 11 KB5066835 caused a serious gaming-performance regression on some systems, particularly in certain games running on NVIDIA GeForce hardware. The cumulative update was released on October 14, 2025 for Windows 11 versions 24H2 and 25H2, producing OS builds 26100.6899 and 26200.6899. NVIDIA later acknowledged that some games could run more slowly after the update and released GeForce Hotfix Driver 581.94 on November 19, 2025.
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The evidence does not support saying that every Windows 11 gaming PC was affected, that every RTX card lost half its frame rate, or that AMD and Intel systems experienced the same problem. The safest description is a substantial but configuration-dependent regression, with the clearest independently tested example involving Assassin’s Creed Shadows on a high-end Ryzen 7 9800X3D and GeForce RTX 5090 system.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsWhat KB5066835 changed
KB5066835 was a cumulative security update for:
- Windows 11 version 24H2: build 26100.6899
- Windows 11 version 25H2: build 26200.6899
- Release date: October 14, 2025
Microsoft’s release notes listed security and quality changes, including a fix for a gamepad-only sign-in scenario in which apps and games could stop responding after sign-in. That listed fix is not the same issue as the later FPS regression. Microsoft’s KB article did not warn users that the update could reduce game performance, and the public Windows release-health documentation did not identify the NVIDIA gaming problem as a Microsoft-known issue.
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How severe was the gaming slowdown?
NVIDIA’s official hotfix documentation said that lower performance could occur in some games after installing KB5066835. NVIDIA did not publish a complete affected-game list, and its wording does not establish a universal frame-rate loss across all GeForce GPUs.
The strongest public independent test came from Digital Foundry, as reported by PCGamesN. In Assassin’s Creed Shadows, testing on an AMD Ryzen 7 9800X3D with an NVIDIA GeForce RTX 5090 reportedly produced approximately:
| Test condition | Reported result |
|---|---|
| Before the NVIDIA hotfix | About 34 FPS in the tested location |
| After the NVIDIA hotfix | About 72 FPS in the same location |
That comparison illustrates how severe the problem could be in an affected game and configuration. It should not be treated as a general benchmark for every RTX card or every copy of Assassin’s Creed Shadows. The underlying testing covered a specific title, system, scene, resolution, and settings.
Who was most likely affected?
The documented scope is narrower than the headline “Windows 11 broke gaming” suggests. The most defensible affected group consists of users who meet all or most of these conditions:
- They were running Windows 11 24H2 or 25H2.
- KB5066835, or a later cumulative update containing the relevant changes, was installed.
- The system used NVIDIA GeForce graphics hardware and a driver in the affected software path.
- One or more games showed lower FPS, worse frame pacing, or unusually low GPU performance after the update.
NVIDIA’s acknowledgment establishes a vendor-specific connection, but it does not prove that every GeForce model was affected. There is also no authoritative evidence in the available documentation establishing an equivalent AMD or Intel regression at comparable rates. Reports involving other graphics vendors should be treated as preliminary unless controlled testing or a vendor statement confirms them.
The documented fix: install NVIDIA driver 581.94
For affected NVIDIA systems, the specific documented mitigation was GeForce Hotfix Driver 581.94, released by NVIDIA on November 19, 2025. NVIDIA described the hotfix as being based on Game Ready Driver 581.80 and listed lower performance in some games after KB5066835 among the addressed issues.
If you are investigating this particular regression, update the graphics driver before considering hardware replacement. A new compatible NVIDIA GeForce RTX graphics card may make sense for an already-planned upgrade, but buying a GPU is not the documented solution to this update-related problem.
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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →How to check whether KB5066835 is installed
Check your Windows build
- Press Windows + R.
- Enter
winverand press Enter. - Record the Windows version and OS build shown in the dialog.
You can also open Settings > System > About and check Windows specifications. Builds 26100.6899 and 26200.6899 correspond to the original KB5066835 release for Windows 11 24H2 and 25H2 respectively. A later build does not prove that the regression is still present; it indicates that the system has received subsequent servicing.
Check update history
- Open Settings > Windows Update.
- Select Update history.
- Expand Quality Updates.
- Look for KB5066835 or a later cumulative update.
Because Windows cumulative updates supersede earlier updates, a current installation may no longer show KB5066835 as the active build even though later servicing includes changes from the October release. Do not remain indefinitely on an old Windows build solely to avoid this historical update; later updates contain important security fixes.
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- 3.6-slot design with massive fin array optimized for airflow from three Axial-tech fans
- Phase-change GPU thermal pad helps ensure optimal thermal performance and longevity, outlasting traditional thermal paste for graphics cards under heavy loads
Check the NVIDIA driver
Open the NVIDIA App or NVIDIA Control Panel and record the installed driver version. You can also check Device Manager > Display adapters > your NVIDIA GPU > Properties > Driver. If the driver is older than the documented 581.94 hotfix, install a current driver appropriate for your GPU. For historical reproduction or troubleshooting, NVIDIA’s 581.94 hotfix is the specifically identified KB5066835 remediation.
Use a controlled before-and-after test
A game may appear slower after an update for reasons unrelated to Windows, including a new game patch, shader compilation, changed graphics settings, thermal throttling, background applications, corrupted driver files, or a different graphics API. A useful comparison requires the same conditions on both runs.
Record the following:
- Windows edition, version, and OS build
- Installed KB numbers
- GPU model and NVIDIA driver version
- Game title and graphics API, if known
- Resolution, quality preset, ray tracing, upscaling, and frame-generation settings
- Average FPS and 1% low FPS
- GPU utilization, clock speed, board power, temperature, and CPU utilization
- The exact test scene, save point, route, or built-in benchmark
Average FPS alone can hide a frame-pacing problem. If average performance is similar but gameplay feels uneven, compare frame-time graphs and 1% lows. If GPU utilization suddenly falls while temperatures and clocks are normal, that may support a software-path investigation, but it does not identify the root cause by itself.
What to do if the driver update does not help
- Repeat the test after a reboot. This removes some transient background and shader-compilation variables.
- Verify game settings. Updates or driver profiles can change resolution scaling, ray tracing, frame limits, or upscaling modes.
- Test another demanding title. A problem limited to one game may be a game update or title-specific issue rather than KB5066835.
- Check temperatures and clocks. Thermal throttling, power limits, or an altered fan profile can resemble an operating-system regression.
- Perform a clean driver installation if appropriate. Preserve your current driver details first, and use the installation options provided by NVIDIA rather than deleting unrelated Windows components.
- Compare with a known-good driver or system state only if necessary. Rollbacks can remove security and game fixes, so treat them as a diagnostic step rather than a permanent recommendation.
If the slowdown remains, document the measurements and report the issue to NVIDIA or the game developer. Include the game build, Windows build, driver version, GPU model, settings, reproducible scene, and frame-time data. “The game feels slower” is much harder to investigate than a repeatable result such as “the same route at the same settings fell from 72 FPS to 34 FPS after the update.”
KB5066835 had other documented problems
The gaming regression was not the only issue associated with KB5066835. Microsoft’s release-health documentation recorded a separate problem in which USB keyboards and mice could stop working inside the Windows Recovery Environment, even though the same devices continued to work normally in Windows itself.
Microsoft recorded that the WinRE USB-input issue was resolved by out-of-band update KB5070773 on October 20, 2025, and by later updates. This separate problem is important because it shows that Microsoft publicly documented some KB5066835 regressions while its public records did not provide a corresponding root-cause statement or Microsoft-specific fix for the NVIDIA gaming-performance issue.
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Microsoft’s October 28, 2025 preview update, KB5067036, also illustrates the normal cumulative-servicing sequence that followed KB5066835 for Windows 11 24H2 and 25H2. Later updates supersede earlier ones, so troubleshooting should focus on the current supported Windows build and the relevant graphics driver rather than treating KB5066835 as an isolated, permanently installed component.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What is known about the root cause?
The timing and testing establish an association, but not a complete technical explanation.
Established by the available evidence
- The slowdown appeared after the October 2025 Windows update in affected scenarios.
- NVIDIA documented lower performance in some games after KB5066835.
- NVIDIA supplied a targeted display-driver hotfix.
- Independent testing reproduced a major performance loss in Assassin’s Creed Shadows and a substantial improvement after the hotfix.
Still unconfirmed
- The exact Windows kernel, graphics-stack, scheduling, or power-management change involved
- Whether Resizable BAR was responsible
- A complete list of affected games and GPU models
- Whether AMD or Intel GPUs experienced the same issue
- Whether every later NVIDIA driver resolved every affected scenario
Unless a primary engineering source provides more detail, claims naming a specific mechanism—such as Resizable BAR—as the definitive cause should be treated as speculation.
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Should you buy a new graphics card?
No—not as the first response to KB5066835. The documented remedy was a driver update, not a hardware replacement. A new card may be reasonable if your GPU was already too slow for your target resolution or games, but it can add considerable cost without addressing a Windows-and-driver interaction.
Only consider a compatible NVIDIA GeForce RTX graphics card after confirming that your existing hardware is inadequate independently of the update, checking power-supply and case requirements, and testing the current driver. The regression report is not evidence that all RTX cards need replacing.
Bottom line
KB5066835 was a real Windows 11 update-related gaming problem for some configurations, not proof that Microsoft broke gaming for every PC. NVIDIA explicitly acknowledged lower performance in some games and released GeForce Hotfix Driver 581.94. The reported Assassin’s Creed Shadows test—roughly 34 FPS before the hotfix versus 72 FPS afterward on a Ryzen 7 9800X3D and RTX 5090—shows the potential severity, but it is not a universal benchmark.
Check your Windows build, update history, GPU driver, and repeatable frame-time results. Install the appropriate current NVIDIA driver before changing hardware, and keep the uncertainty clear: the public evidence identifies the symptom and a practical mitigation, but not a definitive root cause or complete affected-game list.
Frequently Asked Questions
What was Windows 11 KB5066835?
KB5066835 was a Windows 11 cumulative security update released on October 14, 2025 for versions 24H2 and 25H2. It produced builds 26100.6899 and 26200.6899.
How do I fix the KB5066835 gaming-performance regression?
NVIDIA’s GeForce Hotfix Driver 581.94 was the specifically documented mitigation. Install the current compatible NVIDIA driver, then retest the same game scene and settings.
Did KB5066835 reduce FPS on every gaming PC?
No. The available evidence concerns some games and configurations, particularly systems using NVIDIA GeForce hardware. It does not prove that every RTX card, game, or Windows 11 PC was affected.
Which game was most clearly affected?
The strongest independent example involved Assassin’s Creed Shadows on a Ryzen 7 9800X3D and RTX 5090. Reported performance improved from about 34 FPS before the hotfix to about 72 FPS afterward in the same test location.
The Bottom Line
Bottom line: KB5066835 caused severe gaming slowdowns in some Windows 11 24H2 and 25H2 configurations, with the clearest evidence involving NVIDIA GeForce hardware. Install the appropriate NVIDIA driver—historically, GeForce Hotfix Driver 581.94—before considering any hardware replacement. The issue was not universal, and its exact technical cause remains unconfirmed.
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