GPT-5.6 consistently aborts functions.exec / tools.exec_command, while GPT-5.5 works

What version of Codex CLI is running?

codex-cli 0.147.0

What subscription do you have?

Enterprise

Which model were you using?

_No response_

What platform is your computer?

_No response_

What terminal emulator and version are you using (if applicable)?

_No response_

Codex doctor report

What issue are you seeing?

Summary

functions.exec consistently returns aborted when running shell commands with GPT-5.6 models, while the same operation works normally with GPT-5.5.

Reproduction

Run a minimal shell command:

echo hello

The tool call immediately returns:

aborted

No command output, stderr, or exit code is returned.

The issue is reproducible with other trivial commands, including:

pwd
echo hello
python3 --version

It also occurs when invoking the nested JavaScript tool:

const r = await tools.exec_command({
  cmd: "echo hello",
  yield_time_ms: 10000,
  max_output_tokens: 2000
});
text(r.output);

The execution is still aborted before any command output is produced.

Expected behavior

The command should execute successfully and return:

hello

Actual behavior

The execution is aborted before the command produces any output.

There is no stdout, stderr, or exit code returned by the tool call.

Model comparison

• GPT-5.5: works normally
• GPT-5.6: consistently returns aborted
• GPT-5.6-terra: consistently returns aborted

The same Codex CLI installation and environment are used for the model comparison.

Additional observations

• The failure occurs with trivial local commands that do not require network access or special permissions.
• echo hello reproduces the issue, so the failure does not appear to be related to Python, Git, or the repository.
• Changing the working directory, shell options, and command arguments does not resolve the issue.
• Switching to GPT-5.5 immediately restores normal command execution.
• The behavior is consistently reproducible with GPT-5.6 models.

This appears to be a model-specific issue in the tool execution path rather than a failure of the underlying shell command.

Environment

• OS: macOS
• Codex CLI: 0.147.0
• Tool: functions.exec / tools.exec_command
• Model: GPT-5.6 / GPT-5.6-terra
• Working directory: local Git repository
• Architecture: Apple Silicon

Minimal reproduction

Codex CLI 0.147.0
Model: GPT-5.6-terra

User: Run `echo hello`

Tool: functions.exec
Result: aborted

No stdout
No stderr
No exit code

Switching only the model:

Codex CLI 0.147.0
Model: GPT-5.5

User: Run `echo hello`

Tool: functions.exec
Result: hello

The difference is consistently reproducible.

What steps can reproduce the bug?

1. Install and run Codex CLI 0.147.0 on macOS (Apple Silicon).
2. Open a local Git repository with Codex.
3. Select the GPT-5.6-terra model.
4. Ask Codex to execute a trivial shell command, for example:

``sh
echo hello
``

1. Observe that the functions.exec / tools.exec_command call immediately returns aborted.
2. No stdout, stderr, or exit code is returned.
3. Repeat with other trivial commands such as:

``sh
pwd
python3 --version
``

The same behavior occurs.

1. Switch the model to GPT-5.5 and run the same commands.
2. Observe that the commands execute normally and return their expected output.

What is the expected behavior?

_No response_

Additional information

_No response_

echo hello

hello