Temporary Chat does not receive Custom Instructions on macOS and iOS

What version of the Codex / ChatGPT App are you using?

• macOS desktop app: 26.803.41515
• iOS app: 1.2026.209

What subscription do you have?

ChatGPT Plus

What platform are you using?

• macOS desktop app
• iOS

What issue are you seeing?

Temporary Chat does not appear to receive account-level Custom Instructions, even though the same Custom Instructions work correctly in a normal ChatGPT conversation.

This reproduces on both the macOS desktop app and the iOS app.

My Custom Instructions contain a simple test instruction defining g: as a grammar/rewrite command.

In a normal ChatGPT conversation, asking:

What does g: mean according to my custom instructions?

correctly returns the definition from my Custom Instructions.

In a Temporary Chat, asking the exact same question returns:

I don’t see any custom instruction in the context available to me that defines g:. So I can’t reliably say what it means according to your custom instructions.

This strongly suggests that the Custom Instructions are not being injected into the Temporary Chat context at all, rather than merely being ignored by the model.

What steps can reproduce the bug?

1. Enable account-level Custom Instructions.
2. Add an easily testable instruction, for example:
   • g: means "Grammar / rewrite".
3. Start a normal ChatGPT conversation.
4. Ask:
   What does g: mean according to my custom instructions?
5. Confirm that ChatGPT can correctly describe the instruction.
6. Start a new Temporary Chat using the same account.
7. Ask the exact same question.
8. Observe that Temporary Chat says it cannot see any Custom Instruction defining g:.

I reproduced this independently on:

• macOS desktop app 26.803.41515
• iOS app 1.2026.209

The normal-chat control works, while Temporary Chat fails on the same account.

What is the expected behavior?

Temporary Chat should still receive and follow enabled account-level Custom Instructions.

This is also what the current OpenAI documentation explicitly says:

Temporary Chat FAQ:
https://help.openai.com/en/articles/8914046-temporary-chat-faq

"It will still follow your custom instructions if they're enabled."

Custom Instructions documentation:
https://help.openai.com/en/articles/8096356-chatgpt-custom-instructions

The documentation says Custom Instructions are applied to all chats and are available on Web, Desktop, iOS, and Android.

Additional information

Observed on 2026-08-10.

This does not appear to be a general Custom Instructions configuration issue because the same instructions work immediately in a normal ChatGPT conversation.

The failure also occurs across two different clients (macOS and iOS), which suggests this may be related to Temporary Chat session/context construction rather than a client-specific UI bug.

Screenshots are available showing:

1. Normal chat correctly reading the g: Custom Instruction.
2. Temporary Chat saying no such Custom Instruction exists in its available context.

The report names no repository files, tests, or entry points. First reproduce the comparison between normal and Temporary Chat on the listed macOS and iOS versions; done means Temporary Chat receives and follows the enabled account-level Custom Instructions as normal Chat does.