[BUG] Cowork Windows - Display corruption and blackout on 4K DisplayPort primary monitor (NVIDIA T400)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Cowork causes complete display failure on primary 4K monitor when the application window is opened or moved to that display.

Symptom progression:

1. Wallpaper corruption appears
2. Display goes completely black
3. Monitor remains unresponsive until Cowork window is moved to secondary monitor
4. Moving Cowork to Monitor 2 (Dell) immediately restores Monitor 1 (ASUS) functionality

Reproducibility: 100% - occurs every time Cowork window is opened on or moved to Monitor 1
Workaround: Cowork functions normally on Monitor 2 (Dell)
Persistence: Issue persists after reboot

Environment

Operating System:

• Windows 11 Pro 64-bit, Build 26200
• DPI Scaling: 150% (144 DPI)

GPU:

• Model: NVIDIA T400 4GB
• Driver Version: 32.0.15.9159
• Driver Date: December 11, 2025

Claude Desktop Version: 1.1.3189 (1b7b58)

Monitor Configuration (Triple 4K DisplayPort setup):

• Monitor 1 (Primary - AFFECTED):
• Model: ASUS XG32UQ
• Resolution: 3840 × 2160 @ 60Hz
• Connection: DisplayPort
• HDR: Supported (currently SDR mode)

• Monitor 2 (WORKS NORMALLY):
• Model: Dell U2720Q
• Resolution: 3840 × 2160 @ 60Hz
• Connection: DisplayPort
• HDR: Supported (currently SDR mode)

• Monitor 3 (WORKS NORMALLY):
• Model: Lenovo L28u-35
• Resolution: 3840 × 2160 @ 60Hz
• Connection: DisplayPort
• HDR: Supported (currently SDR mode)

Note: All three monitors have identical technical specifications (4K, 60Hz, DisplayPort, HDR). The issue only occurs on Monitor 1 (ASUS, designated as Windows primary display).

What Should Happen?

Expected Behavior

Cowork window should display normally on any 4K DisplayPort monitor without causing display corruption or signal loss.

Actual Behavior

Opening Cowork on Monitor 1 (ASUS XG32UQ, primary display) triggers:

• Visual artifacts (wallpaper corruption)
• Complete display signal loss (black screen)
• Monitor unrecoverable until application moved to Monitor 2 or 3

Error Messages/Logs

## Additional Context

**Significant observation:** All three monitors have identical technical specifications (4K @ 60Hz via DisplayPort, same GPU, same driver, same HDR capabilities), yet only the primary display (ASUS) exhibits this behavior. This suggests the issue may be related to:
1. Windows primary display designation, OR
2. ASUS XG32UQ-specific firmware/EDID, OR
3. Some interaction between Cowork and primary display detection

The immediate recovery when moving the window to Monitor 2 suggests Cowork is issuing display mode or compositor commands that this specific configuration cannot handle.

This appears to be a display mode switching or compositor interaction issue specific to the primary monitor in multi-monitor 4K DisplayPort configurations on NVIDIA T400.

Steps to Reproduce

Steps to Reproduce

1. Install Claude Desktop on Windows 11 Pro with NVIDIA T400 GPU
2. Configure triple 4K DisplayPort monitor setup with ASUS XG32UQ as primary
3. Open Cowork
4. Observe wallpaper corruption followed by display blackout on Monitor 1 (ASUS)
5. Move Cowork window to Monitor 2 (Dell)
6. Monitor 1 immediately recovers

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Cowork Version 1.1.3189 (1b7b58)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_