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Codex Issues / #12962

Codex app-server crashes on Windows 11 build 26200 (HW capability error)

Open 💬 6 comments Opened Feb 26, 2026 by lucasmatostech
💡 Likely answer: A maintainer (github-actions[bot], contributor) responded on this thread — see the highlighted reply below.

What version of the Codex App are you using (From “About Codex” dialog)?

0.4.78

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Windows 11 Home 10.0.26200 x64 AMD Ryzen 7 5700X3D

What issue are you seeing?

When activating the Codex extension in VS Code on Windows 11 (build 26200), the app-server crashes immediately.

Error log:

Fatal Error: HW capability found: 0x178BFBFF 0x7EF8320B, but HW capability requested: 0x200000 0x00.

[CodexMcpConnection] Codex app-server process exited unexpectedly (code=3221226505, 0xc0000409)

Environment:

  • Windows 11 Home 10.0.26200
  • AMD Ryzen 7 5700X3D (AVX2 supported)
  • Secure Boot: Enabled
  • Hyper-V: Disabled
  • Virtualization-based Security: Not enabled
  • Codex version: 0.4.78 (Release)
  • VS Code latest stable

The CPU fully supports AVX2 and modern instruction sets.
This appears to be an incompatibility between the Codex native app-server binary and Windows 11 build 26200.

What steps can reproduce the bug?

Steps to reproduce:

  1. Install VS Code (latest stable).
  2. Install the "Codex – OpenAI’s coding agent" extension (version 0.4.78 Release).
  3. Ensure Windows 11 Home build 26200 is running.
  4. Confirm Hyper-V and Virtualization-based Security are disabled.
  5. Open VS Code.
  6. Activate the Codex extension (click Codex panel or trigger activation).

Result:
The Codex app-server crashes immediately on activation.

Error in logs:

Fatal Error: HW capability found: 0x178BFBFF 0x7EF8320B, but HW capability requested: 0x200000 0x00.
Exit code: 3221226505 (0xc0000409)

Expected behavior:
Codex app-server should start normally.

What is the expected behavior?

_No response_

Additional information

_No response_

View original on GitHub ↗

6 Comments

github-actions[bot] contributor · 4 months ago

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

  • #12899

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Murilo695 · 3 months ago

I’m seeing a very similar problem on Windows build 26200.

My Codex Windows app crashes immediately on launch.

Environment:

  • OS: Windows 11 build 26200.8037
  • CPU: AMD Ryzen 5 5500
  • Motherboard: Gigabyte B550M AORUS ELITE

Windows Event Viewer shows:

  • Failing application: codex.exe
  • codex.exe version: 0.115.0.0
  • Failing module: ucrtbase.dll
  • Exception code: 0xc0000409
  • Package: OpenAI.Codex_26.313.5234.0_x64__2p2nqsd0c76g0
  • Path: C:\Program Files\WindowsApps\OpenAI.Codex_26.313.5234.0_x64__2p2nqsd0c76g0\app\resources\codex.exe

What I already tried:

  • Repair app
  • Reset app
  • Reinstall app from Microsoft Store
  • Update AMD chipset drivers
  • Disable XMP and PBO in BIOS
  • Test with ~/.codex/config.toml:

[windows]
sandbox = "unelevated"

The crash happens before ~/.codex logs/sessions are created.

apocalx · 3 months ago

Not a repro — posting as a distribution + architecture isolation data point, since both existing reports in this thread are AMD Ryzen.

Environment

  • Windows 11 Home 10.0.26200.8246
  • Intel Core i9-13900HX
  • codex-cli 0.121.0 installed via npm — not the Microsoft Store app or the VS Code extension

Test: launched codex app-server directly over stdio and sent an initialize JSON-RPC request.

Result: valid InitializeResponse returned (platformOs: windows, platformFamily: windows), exit 0, no 0xc0000409, empty stderr. codex app-server generate-json-schema also succeeded cleanly.

Tentative take: both existing reports are AMD Ryzen on Win11 26200. A clean run on Intel on the same build line suggests the HW capability crash may be AMD-specific rather than a general Win11 26200 issue — though the standalone CLI binary may also differ from the bundled binary used by the Store app / VS Code extension, which is a separate variable. Happy to run additional probes if useful.

ShanireZ · 2 months ago

I guess the command setx OPENSSL_ia32cap ~0x20000000 maybe could solve this problem.
Run it and don't forget restart the powershell.

rayanovelha · 2 months ago
I guess the command setx OPENSSL_ia32cap ~0x20000000 maybe could solve this problem. Run it and don't forget restart the powershell.

Thanks this solved the problem for me

CodenameCookie · 2 months ago
I guess the command setx OPENSSL_ia32cap ~0x20000000 maybe could solve this problem. Run it and don't forget restart the powershell.

Worked for me to get Codex CLI running and Codex App. Thank you
Just had to restart my machine after running that command and both were fine