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Codex app-server crashes on Windows 11 build 26200 (HW capability error) #12962

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Codex app-server crashes on Windows 11 build 26200 (HW capability error)#12962
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app-serverIssues involving app server protocol or interfacesbugSomething isn't workingregressionBehaviors that worked in previous versions but were broken due to an updatewindows-osIssues related to Codex on Windows systems

Description

@lucasmatostech
lucasmatostech
opened on Feb 26, 2026

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

Activity

  1. lucasmatostech
    added
    appIssues related to the Codex desktop app
    on Feb 26, 2026
  2. github-actions
    added
    bugSomething isn't working
    extensionIssues related to the VS Code extension
    windows-osIssues related to Codex on Windows systems
    on Feb 26, 2026

  3. github-actions commented on Feb 26, 2026

    @github-actions
    github-actionsBot
    on Feb 26, 2026 – with GitHub Actions
    Contributor

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

    Powered by Codex Action

  4. etraut-openai
    marked Windows regression in Codex CLI — version 0.105+ crashes with HW capability error (0x20000000) #13473 as a duplicate of this issue on Mar 4, 2026
  5. etraut-openai
    marked Codex fails to start on Windows with CPU capability error (requested: 0x20000000) #12899 as a duplicate of this issue on Mar 4, 2026
  6. etraut-openai
    added
    regressionBehaviors that worked in previous versions but were broken due to an update
    and removed
    appIssues related to the Codex desktop app
    extensionIssues related to the VS Code extension
    on Mar 4, 2026
  7. etraut-openai
    added
    agentIssues related to the core agent loop
    on Mar 16, 2026

  8. Murilo695 commented on Mar 25, 2026

    @Murilo695
    Murilo695
    on Mar 25, 2026

    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.

  9. etraut-openai
    added
    app-serverIssues involving app server protocol or interfaces
    and removed
    agentIssues related to the core agent loop
    on Apr 11, 2026

  10. apocalx commented on Apr 19, 2026

    @apocalx
    apocalx
    on Apr 19, 2026

    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.

  11. ShanireZ commented on Apr 25, 2026

    @ShanireZ
    ShanireZ
    on Apr 25, 2026

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

  12. rayanovelha commented on Apr 27, 2026

    @rayanovelha
    rayanovelha
    on Apr 27, 2026

    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

  13. CodenameCookie commented on May 1, 2026

    @CodenameCookie
    CodenameCookie
    on May 1, 2026

    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

  14. Autokratoros commented on Aug 23, 2026

    @Autokratoros
    Autokratoros
    on Aug 23, 2026

    Hitting the same crash on Windows 11 build 26200 (OS build 10.0.26200). Confirmed it's not a corrupted install -- fully removed the Appx package (Get-AppxPackage OpenAI.Codex | Remove-AppxPackage) and reinstalled clean from the Microsoft Store; identical error afterward, same hex values.

    HW capability found: 0x178BFBFF 0xFED8320B, but HW capability requested: 0x20000000 0x00

    Notable: bit 29 (0x20000000) in the "requested" mask maps to F16C in the standard CPUID leaf-1 ECX layout -- normally always present alongside AVX (bit 28, which is set in "found") on any CPU from the last ~13 years. That specific pattern -- AVX visible but F16C invisible to user-mode CPUID -- is a known symptom of Hyper-V CPUID masking, which activates whenever Memory Integrity (Core Isolation/VBS) is running. On this machine, Win32_DeviceGuard confirms VirtualizationBasedSecurityStatus: 2 (running) with SecurityServicesRunning: {2} (Memory Integrity active). Haven't disabled it to confirm since that's a real security trade-off for one app, but this looks like the actual root cause rather than a packaging issue.

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