ChatGPT Desktop sends unsupported reasoning.summary parameter to GPT-5.3-Codex-Spark

What version of the Codex App are you using (From “About Codex” dialog)?

26.707.71524

What subscription do you have?

PRO20X

What platform is your computer?

macOS

What issue are you seeing?

Subject:
GPT-5.3-Codex-Spark fails in ChatGPT Desktop but works in bundled Codex CLI

Description:

I found a reproducible issue with ChatGPT Desktop.

Environment:

• ChatGPT Desktop: 26.707.71524 (official DMG)
• macOS 26.4
• ChatGPT Pro
• GPT-5.3-Codex-Spark quota: 100% remaining

Problem:

Using GPT-5.3-Codex-Spark inside the ChatGPT Desktop Codex UI always fails immediately with:

Unsupported parameter:
'reasoning.summary'
is not supported with the
'gpt-5.3-codex-spark'
model.

This happens even when sending a simple prompt like:

hello

However, the bundled Codex runtime works perfectly.

I tested:

/Applications/ChatGPT.app/Contents/Resources/codex chat

Then switched to:

/model gpt-5.3-codex-spark

and sent:

hello

Everything works normally.

Additional diagnostics:

• codex doctor passes all checks
• Authentication OK
• WebSocket OK (HTTP 101)
• Configuration OK
• models_cache.json correctly contains gpt-5.3-codex-spark
• config.toml does not contain reasoning.summary

This appears to be an issue in the ChatGPT Desktop Codex GUI, not the runtime.

Could you please:

1. confirm whether this is a known issue,
2. escalate it to the engineering team,
3. and, if possible, restore or compensate the unusable Spark quota consumed during troubleshooting?

Thank you.

What steps can reproduce the bug?

1. Open ChatGPT Desktop (Version 26.707.71524).

1. Open Codex.

1. Create a new chat.

1. Select "GPT-5.3-Codex-Spark".

1. Use any reasoning effort (Low / Medium / High).

1. Send a simple message:

hello

Result:

The Desktop UI immediately returns:

Unsupported parameter:
'reasoning.summary'
is not supported with the
'gpt-5.3-codex-spark'
model.

Expected:

The model should respond normally.

What is the expected behavior?

GPT-5.3-Codex-Spark should accept the request and respond normally in the ChatGPT Desktop Codex UI, exactly as it does when using the bundled Codex runtime.

No "Unsupported parameter: reasoning.summary" error should occur.

Additional information

Additional information:

I spent considerable time troubleshooting before reporting.

I verified the following:

• ChatGPT Desktop is the latest version (26.707.71524)
• ChatGPT Pro account
• GPT-5.3-Codex-Spark quota remains at 100%
• Bundled Codex runtime works correctly:
/Applications/ChatGPT.app/Contents/Resources/codex chat

/model gpt-5.3-codex-spark

hello

-> responds normally

• codex doctor passes all checks
• Authentication OK
• WebSocket OK (HTTP 101)
• Configuration OK
• models_cache.json contains gpt-5.3-codex-spark
• config.toml does not contain reasoning.summary

This appears to be a Desktop GUI issue rather than a runtime or account issue.

I also spent a significant amount of time and Codex usage investigating this issue. If this is confirmed to be a product bug, I would appreciate any consideration for restoring or compensating the usage consumed during troubleshooting.