AC Shadows - Performance Issue with High End Nvidia Cards - What Grok has to say

[Nobby]

**The "resizable bar issue" (also called ReBAR or Resizable BAR) with Assassin's Creed Shadows refers to a performance bug primarily affecting PC players with NVIDIA GPUs (like RTX 4070/5070 Ti, 4080/5080, 5090 series), especially after specific Windows 11 updates such as the October 2025 cumulative update KB5066835 (OS build 26100.6899) or 25H2.<grok:render card_id="8741de" card_type="citation_card" type="render_inline_citation">
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**Symptoms include:**
- Severe FPS drops (33-50% or more, e.g., from 72 FPS to 34 FPS at 4K with DLSS Quality on an RTX 5090 paired with Ryzen 7 9800X3D).<grok:render card_id="caab85" card_type="citation_card" type="render_inline_citation">
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- Stuttering, low 1% lows, and unplayable frame times despite high average FPS.<grok:render card_id="817337" card_type="citation_card" type="render_inline_citation">
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- GPU stuck at 95-100% utilization but with drastically reduced power draw/TDP (e.g., 120-155W instead of 300W+), making the game reliant on Frame Generation for playability.<grok:render card_id="6df2ab" card_type="citation_card" type="render_inline_citation">
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- Issues are game-specific; other titles run fine at full power.<grok:render card_id="7dec83" card_type="citation_card" type="render_inline_citation">
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**Affected setups:**
- NVIDIA RTX 40/50-series GPUs (AMD/Intel GPUs unaffected).<grok:render card_id="536439" card_type="citation_card" type="render_inline_citation">
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- Often worse on AMD CPUs (e.g., Ryzen).<grok:render card_id="658418" card_type="citation_card" type="render_inline_citation">
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- Triggered by Windows 11 updates interacting poorly with NVIDIA drivers and ReBAR (a PCIe feature for better CPU-GPU VRAM access).<grok:render card_id="4dcf6b" card_type="citation_card" type="render_inline_citation">
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**Note:** Ubisoft support often recommends *enabling* ReBAR (plus Hardware-Accelerated GPU Scheduling) as a general fix for performance/stuttering.<grok:render card_id="7e0dfe" card_type="citation_card" type="render_inline_citation">
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</grok:render> However, for this specific bug, *disabling* it is the key workaround.<grok:render card_id="ea5497" card_type="citation_card" type="render_inline_citation">
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**Fixes and workarounds (in order of recommendation):**
1. **Install NVIDIA GeForce Hotfix Driver 581.94** (released Nov 19, 2025): Directly addresses the low performance after KB5066835 in AC Shadows and similar games. Download the DCH version for Win10/11 x64 from NVIDIA's site (international.download.nvidia.com/Windows/581.94hf/...). Use a clean install via GeForce Experience or manual method. Many users report full TDP restoration and playable FPS, though some say it's partial.<grok:render card_id="14ce8a" card_type="citation_card" type="render_inline_citation">
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2. **Disable ReBAR in BIOS** (especially for AMD CPU + NVIDIA GPU setups): Enter BIOS (usually Del/F2 on boot), find "Resizable BAR," "Re-Size BAR Support," or "Above 4G Decoding" under PCIe/Advanced settings, and turn it off. Save/exit. This bypasses the bug (NVIDIA's game profile already disables it, but BIOS override is needed). Users confirm FPS/TDP jumps (e.g., from 12 FPS to smooth). Re-enable later for other games if desired.<grok:render card_id="d811c1" card_type="citation_card" type="render_inline_citation">
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3. **Uninstall problematic Windows updates**: Go to Settings > Windows Update > Update history > Uninstall updates. Remove KB5066835, KB5066131, or recent October ones. Or use Command Prompt (admin): `wusa /uninstall /kb:5066835`. Pause updates afterward. Rolls back to pre-bug performance (e.g., 100+ FPS).<grok:render card_id="c6a5e8" card_type="citation_card" type="render_inline_citation">
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4. **Other tweaks:** Verify game files, disable overlays (Discord/Steam), cap FPS, or upvote Ubisoft's bug tracker (ACSH-18450) for a permanent patch.<grok:render card_id="3cc83d" card_type="citation_card" type="render_inline_citation">
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The hotfix and BIOS disable resolve it for most; a full driver (post-581.94) may follow. AMD GPUs sidestep this entirely.<grok:render card_id="8d243c" card_type="citation_card" type="render_inline_citation">
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