claude-code - 💡(How to fix) Fix [BUG] Desktop app crashes (exit code 3221225477) with Sonnet but not Opus on Windows 11

Preflight Checklist

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

What's Wrong?

Title: Desktop app crashes (exit code 3221225477) with Sonnet but not Opus on Windows 11

Describe the bug The Claude Code desktop app crashes every time a session is started or a message is sent when using the Sonnet model. Switching to Opus resolves the crash immediately. The issue is 100% reproducible by toggling between models.

To reproduce

1. Open Claude Code desktop app on Windows 11
2. Set model to Sonnet (claude-sonnet-4-6)
3. Start or resume any session
4. Observe crash: Claude Code process exited with code 3221225477
5. Switch model to Opus — session works normally
6. Switch back to Sonnet — crash returns

Expected behavior Sessions should initialize and respond normally on Sonnet, as they do on Opus.

Error message Claude Code process exited with code 3221225477 Exit code 3221225477 = 0xC0000005 (Windows STATUS_ACCESS_VIOLATION)

Log excerpt (%APPDATA%\Claude\logs\main.log) [warn] [CCD] sendMessage on uninitialized session (CLI died before init); restarting via startSession [error] Session query error: Claude Code process exited with code 3221225477 [info] [CCD CycleHealth] unhealthy cycle (12s, hadFirstResponse=false, reason=no_response)

Sentry event IDs

• de220a97a1eb40e3802a4e157a857373
• db0f3c9fda684cf790c2228d8d2c6f86

Environment

• OS: Windows 11 Home 10.0.26200
• Desktop app version: 1.8555.2.0 (installed via Microsoft Store / WindowsApps)
• CLI binary version: 2.1.149
• CLI path: %APPDATA%\Claude\claude-code\2.1.149\claude.exe

Additional context

• The CLI binary itself runs fine standalone (claude.exe --version returns correctly)
• The crash only occurs when the desktop app spawns it as a subprocess for a session
• Opus works without issue in the same app, same session, same machine
• AV exclusions have been added for %APPDATA%\Claude — no effect on Sonnet crash
• Fresh binary re-download did not resolve the issue

What Should Happen?

it should not crash

Error Messages/Logs

Title: Desktop app crashes (exit code 3221225477) with Sonnet but not Opus on Windows 11

  Describe the bug
  The Claude Code desktop app crashes every time a session is started or a message is sent when using the Sonnet model.
  Switching to Opus resolves the crash immediately. The issue is 100% reproducible by toggling between models.

  To reproduce
  1. Open Claude Code desktop app on Windows 11
  2. Set model to Sonnet (claude-sonnet-4-6)
  3. Start or resume any session
  4. Observe crash: Claude Code process exited with code 3221225477
  5. Switch model to Opus — session works normally
  6. Switch back to Sonnet — crash returns

  Expected behavior
  Sessions should initialize and respond normally on Sonnet, as they do on Opus.

  Error message
  Claude Code process exited with code 3221225477
  Exit code 3221225477 = 0xC0000005 (Windows STATUS_ACCESS_VIOLATION)

  Log excerpt (%APPDATA%\Claude\logs\main.log)
  [warn] [CCD] sendMessage on uninitialized session (CLI died before init); restarting via startSession
  [error] Session query error: Claude Code process exited with code 3221225477
  [info] [CCD CycleHealth] unhealthy cycle (12s, hadFirstResponse=false, reason=no_response)

  Sentry event IDs
  - de220a97a1eb40e3802a4e157a857373
  - db0f3c9fda684cf790c2228d8d2c6f86

  Environment
  - OS: Windows 11 Home 10.0.26200
  - Desktop app version: 1.8555.2.0 (installed via Microsoft Store / WindowsApps)
  - CLI binary version: 2.1.149
  - CLI path: %APPDATA%\Claude\claude-code\2.1.149\claude.exe

  Additional context
  - The CLI binary itself runs fine standalone (claude.exe --version returns correctly)
  - The crash only occurs when the desktop app spawns it as a subprocess for a session
  - Opus works without issue in the same app, same session, same machine
  - AV exclusions have been added for %APPDATA%\Claude — no effect on Sonnet crash
  - Fresh binary re-download did not resolve the issue

Steps to Reproduce

Title: Desktop app crashes (exit code 3221225477) with Sonnet but not Opus on Windows 11

Describe the bug The Claude Code desktop app crashes every time a session is started or a message is sent when using the Sonnet model. Switching to Opus resolves the crash immediately. The issue is 100% reproducible by toggling between models.

To reproduce

1. Open Claude Code desktop app on Windows 11
2. Set model to Sonnet (claude-sonnet-4-6)
3. Start or resume any session
4. Observe crash: Claude Code process exited with code 3221225477
5. Switch model to Opus — session works normally
6. Switch back to Sonnet — crash returns

Expected behavior Sessions should initialize and respond normally on Sonnet, as they do on Opus.

Error message Claude Code process exited with code 3221225477 Exit code 3221225477 = 0xC0000005 (Windows STATUS_ACCESS_VIOLATION)

Log excerpt (%APPDATA%\Claude\logs\main.log) [warn] [CCD] sendMessage on uninitialized session (CLI died before init); restarting via startSession [error] Session query error: Claude Code process exited with code 3221225477 [info] [CCD CycleHealth] unhealthy cycle (12s, hadFirstResponse=false, reason=no_response)

Sentry event IDs

• de220a97a1eb40e3802a4e157a857373
• db0f3c9fda684cf790c2228d8d2c6f86

Environment

• OS: Windows 11 Home 10.0.26200
• Desktop app version: 1.8555.2.0 (installed via Microsoft Store / WindowsApps)
• CLI binary version: 2.1.149
• CLI path: %APPDATA%\Claude\claude-code\2.1.149\claude.exe

Additional context

• The CLI binary itself runs fine standalone (claude.exe --version returns correctly)
• The crash only occurs when the desktop app spawns it as a subprocess for a session
• Opus works without issue in the same app, same session, same machine
• AV exclusions have been added for %APPDATA%\Claude — no effect on Sonnet crash
• Fresh binary re-download did not resolve the issue

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No response

Claude Code Version

v2.1.149

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Title: Desktop app crashes (exit code 3221225477) with Sonnet but not Opus on Windows 11

Describe the bug The Claude Code desktop app crashes every time a session is started or a message is sent when using the Sonnet model. Switching to Opus resolves the crash immediately. The issue is 100% reproducible by toggling between models.

To reproduce

1. Open Claude Code desktop app on Windows 11
2. Set model to Sonnet (claude-sonnet-4-6)
3. Start or resume any session
4. Observe crash: Claude Code process exited with code 3221225477
5. Switch model to Opus — session works normally
6. Switch back to Sonnet — crash returns

Expected behavior Sessions should initialize and respond normally on Sonnet, as they do on Opus.

Error message Claude Code process exited with code 3221225477 Exit code 3221225477 = 0xC0000005 (Windows STATUS_ACCESS_VIOLATION)

Log excerpt (%APPDATA%\Claude\logs\main.log) [warn] [CCD] sendMessage on uninitialized session (CLI died before init); restarting via startSession [error] Session query error: Claude Code process exited with code 3221225477 [info] [CCD CycleHealth] unhealthy cycle (12s, hadFirstResponse=false, reason=no_response)

Sentry event IDs

• de220a97a1eb40e3802a4e157a857373
• db0f3c9fda684cf790c2228d8d2c6f86

Environment

• OS: Windows 11 Home 10.0.26200
• Desktop app version: 1.8555.2.0 (installed via Microsoft Store / WindowsApps)
• CLI binary version: 2.1.149
• CLI path: %APPDATA%\Claude\claude-code\2.1.149\claude.exe

Additional context

• The CLI binary itself runs fine standalone (claude.exe --version returns correctly)
• The crash only occurs when the desktop app spawns it as a subprocess for a session
• Opus works without issue in the same app, same session, same machine
• AV exclusions have been added for %APPDATA%\Claude — no effect on Sonnet crash
• Fresh binary re-download did not resolve the issue