GPT-5.4 frequently reports tasks as completed without executing them (returns previous outputs, false completion, or unperformed actions)

What issue are you seeing?

This issue appears to have started several hours after the release and was not present immediately at launch. (maybe.)

After issuing a task instruction, the following behaviors repeatedly occur. I have been experiencing this continuously for five days:

1. The model says it “will do it”, but then simply outputs the result from the previous turn instead of performing the task.
2. The model says it will do it, performs a read action, explains roughly what it plans to do, and then claims the task is finished even though nothing was actually executed.
3. The model does not even state that it will perform the task, but immediately claims “it’s done” while again returning the previous turn’s output.
4. The model says it will do the task, spawns multiple agents, but does not collect their results, and still outputs a result while falsely claiming that all agents were collected and the task was completed.

Additionally, the model often:

• Does not follow the given instructions properly
• Takes shortcuts and pretends the task was completed
• Claims that something possible is impossible and refuses to perform it
• In general, it behaves as if it is deceiving the user by pretending work was done when it was not

This issue only occurs with GPT-5.4.

Important notes:

• The issue occurs regardless of reasoning effort settings
• It occurs both in fast mode and non-fast mode
• It has not occurred in GPT-5.2, which I am currently forced to use because of this problem.

What steps can reproduce the bug?

1. Use GPT-5.4 as the model.
2. Provide a task that requires multi-step execution (e.g., reading files, spawning agents, or performing structured tasks).
3. Observe the response.

Typical reproduction patterns:

• The model says it will execute the task but returns the previous turn’s result.
• The model describes a plan but never executes it, then claims completion.
• The model skips execution entirely and claims the task is finished.
• The model spawns agents but never retrieves their results, while claiming the agents completed their work.

This behavior occurs intermittently but frequently enough to make the model unreliable for task execution workflows.

What is the expected behavior?

• If the model says it will perform a task, it should actually execute the described steps.
• The model should not claim completion / pretend completion unless the task has been executed.
• The model should not return previous outputs as if they are new results.

Additional information

• The issue did not appear immediately after GPT-5.4 release but started occurring a few hours later. (maybe?)
• The problem has persisted for five consecutive days.
• The same workflows function correctly in GPT-5.2, suggesting a regression specific to GPT-5.4. However, the behavior currently observed in GPT-5.4 feels similar to what I experienced with 5.3-codex-spark/5.3-codex/5.2-codex: the model often acts autonomously, fails to follow instructions, and frequently appears to pretend that tasks were completed.
• Reasoning effort settings (low, medium, high, xhigh) do not affect the issue.
• Fast mode does not affect the issue.
• AGENTS.md does not affect the issue.