Summary
After Codex CLI auto-updated to @openai/codex@0.135.0 on Windows, the CLI native binary started crashing immediately on a Haswell-era CPU with Windows exit code -1073741795 (0xC000001D, STATUS_ILLEGAL_INSTRUCTION).
Downgrading to @openai/codex@0.134.0 restores startup on the same machine. This looks like a Windows x64 native binary CPU-instruction baseline regression in 0.135.0.
Environment
- Product: Codex CLI installed via npm (
@openai/codex)
- Affected version:
0.135.0
- Last known working version on the same host:
0.134.0
- OS:
Microsoft Windows NT 10.0.22631.0 x64
- CPU:
Intel(R) Xeon(R) CPU E3-1230 v3 @ 3.30GHz
- Haswell generation, 2013
- Supports AVX2 but does not support AVX-512
- 4 cores / 8 logical processors
- Node.js:
v24.15.0
- npm:
11.12.1
- Current workaround state: pinned back to
codex-cli 0.134.0
Observed behavior
At approximately 2026-05-31 12:38 CST, Codex auto-updated to 0.135.0. After that, the normal launcher could no longer start Codex. It reported:
Codex CLI exited with code -1073741795
-1073741795 is 0xC000001D, i.e. STATUS_ILLEGAL_INSTRUCTION on Windows. The launcher fell back to its recovery shell / cmd prompt.
In local diagnosis, light wrapper paths such as codex --help did not reproduce the immediate crash, but paths that start the real interactive / execution native runtime (codex exec or the normal TUI launcher) crashed immediately.
Expected behavior
@openai/codex@0.135.0 should start on Windows x64 machines that satisfy the intended support baseline, or should fail gracefully with a clear CPU capability error before launching the native runtime.
If Codex CLI intends to support older x86-64 CPUs such as Haswell, the Windows x64 binary should not be built with instructions unavailable on that baseline. If Haswell is no longer supported, the installer / launcher should detect and report that explicitly instead of crashing with STATUS_ILLEGAL_INSTRUCTION.
Reproduction outline
I am not reinstalling 0.135.0 on this production host again because it breaks the local agent launcher, but the observed sequence was:
- Windows x64 host with Intel Xeon E3-1230 v3 / Haswell CPU.
- Codex CLI auto-updates or is installed as
@openai/codex@0.135.0.
- Start Codex through the normal CLI/TUI launcher or execution path.
- Process exits immediately with Windows code
-1073741795 / 0xC000001D.
- Downgrade to
@openai/codex@0.134.0 on the same machine.
- Codex starts again; launcher no longer hits the immediate illegal-instruction crash.
Workaround
Pin Codex CLI to 0.134.0:
npm install -g @openai/codex@0.134.0 --registry https://registry.npmmirror.com
codex --version
# codex-cli 0.134.0
I also added a local launcher pre-flight that checks the installed Codex version and re-pins to 0.134.0 if a later auto-update reappears, because the trigger for the auto-update has not yet been identified.
Related observations
There are existing Windows 0xC000001D / binary startup issues in this repo, but I did not find an exact duplicate for Codex CLI 0.135.0 + Haswell CPU + npm package @openai/codex-win32-x64.
This may be related to a build-toolchain or CPU target change in the 0.135.0 Windows x64 native binary. Please check whether the Windows x64 artifact is being built with a CPU baseline above generic x86-64 / Haswell-compatible instructions, or whether a dependency/runtime path introduced an AVX-512 requirement.
Summary
After Codex CLI auto-updated to
@openai/codex@0.135.0on Windows, the CLI native binary started crashing immediately on a Haswell-era CPU with Windows exit code-1073741795(0xC000001D,STATUS_ILLEGAL_INSTRUCTION).Downgrading to
@openai/codex@0.134.0restores startup on the same machine. This looks like a Windows x64 native binary CPU-instruction baseline regression in0.135.0.Environment
@openai/codex)0.135.00.134.0Microsoft Windows NT 10.0.22631.0x64Intel(R) Xeon(R) CPU E3-1230 v3 @ 3.30GHzv24.15.011.12.1codex-cli 0.134.0Observed behavior
At approximately 2026-05-31 12:38 CST, Codex auto-updated to
0.135.0. After that, the normal launcher could no longer start Codex. It reported:-1073741795is0xC000001D, i.e.STATUS_ILLEGAL_INSTRUCTIONon Windows. The launcher fell back to its recovery shell / cmd prompt.In local diagnosis, light wrapper paths such as
codex --helpdid not reproduce the immediate crash, but paths that start the real interactive / execution native runtime (codex execor the normal TUI launcher) crashed immediately.Expected behavior
@openai/codex@0.135.0should start on Windows x64 machines that satisfy the intended support baseline, or should fail gracefully with a clear CPU capability error before launching the native runtime.If Codex CLI intends to support older x86-64 CPUs such as Haswell, the Windows x64 binary should not be built with instructions unavailable on that baseline. If Haswell is no longer supported, the installer / launcher should detect and report that explicitly instead of crashing with
STATUS_ILLEGAL_INSTRUCTION.Reproduction outline
I am not reinstalling
0.135.0on this production host again because it breaks the local agent launcher, but the observed sequence was:@openai/codex@0.135.0.-1073741795/0xC000001D.@openai/codex@0.134.0on the same machine.Workaround
Pin Codex CLI to
0.134.0:I also added a local launcher pre-flight that checks the installed Codex version and re-pins to
0.134.0if a later auto-update reappears, because the trigger for the auto-update has not yet been identified.Related observations
There are existing Windows
0xC000001D/ binary startup issues in this repo, but I did not find an exact duplicate forCodex CLI 0.135.0 + Haswell CPU + npm package @openai/codex-win32-x64.This may be related to a build-toolchain or CPU target change in the
0.135.0Windows x64 native binary. Please check whether the Windows x64 artifact is being built with a CPU baseline above generic x86-64 / Haswell-compatible instructions, or whether a dependency/runtime path introduced an AVX-512 requirement.