This is a bug, not a downgrade for the free tier (or at least not just free tier). I’m using a paid option (Plus) and hit the same issue. 5.4 Keep appearing and disappearing between launches, both 5.4 and 5.3 Codex is unusable.
Free tier here, I got {"detail":"The 'gpt-5.3-codex' model is not supported when using Codex with a ChatGPT account."} as well in VS Code. The option is still available in the dropdown, and is selected by default, so basically everyone who tries to use Codex today is going to get hit with this message.
Also, I don’t know if 5.2 is just slower or what but it is going sloooow…
Looking for verification, this appears to be the official …
We’ve limited access to our latest models (gpt-5.3-codex and gpt-5.4) to paid subscriptions. This is necessary to ensure capacity for paid subscribers. If you’re on a Free plan, you can still use Codex with other models including gpt-5.2-codex.
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so any fixed so far? are they aware? why doesnt it say upgrade or smt..
why there is around 20 people complaining in the whole world?
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Same for me, same line appears.
{“detail”:“The ‘gpt-5.4’ model is not supported when using Codex with a ChatGPT account.”}
I urge the developers to fix this bug as soon as possible.
The only current working model is still usable.
GPT 5.1 → Only up to GPT 5.2
same issue {“detail”:“The ‘gpt-5.3-codex’ model is not supported when using Codex with a ChatGPT account.”}
Only up to GPT 5.2
Lol. So the official OpenAI GitHub account locked the thread there, but they couldn’t be bothered to give actual answers.
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I have the Error Message “{“detail”:“The ‘gpt-5.3-codex’ model is not supported when using Codex with a ChatGPT account.”}”.
What is the solution for that?
Thanks.
yea they locked after my comment
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It is not a bug for free accounts.
It is a bug for paid accounts and should be reported. See below.
Read the details in the image noted in the reply marked as solution. Thanks to PaulBellow for finding the official reply.
We’ve limited access to our latest models (gpt-5.3-codex and gpt-5.4) to paid subscriptions. This is necessary to ensure capacity for paid subscribers. If you’re on a Free plan, you can still use Codex with other models including gpt-5.2-codex.
I am on a paid plan and having the same issue since yesterday evening. No 5.3-codex or 5.4 and getting the same message.
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Which paid plan? 
A later reply in the issues topic
if you’re seeing this on a paid subscription plan, please open a new bug report and provide details requested in the bug report template.
To report a new issue use the GitHub OpenAI Codex issue tab.
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Chatgpt Plus - $20/month plan
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Thank you.
Please see update in my reply to open a new issue and report it.
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Thanks @EricGT for pointing this out.
It appears the team is currently working hard to keep up with a surge in demand.
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Thanks but this did not work for me. the issue appears to be server side because I continue to get the message, which started last night at 9pm:
{“detail”:“The ‘gpt-5.3-codex’ model is not supported when using Codex with a ChatGPT account.”}
I still get it also 
One thing I miss in version 5.2 is this:
Now I want PhoneBank to retrieve traffic tickets from our database, since before it retrieved them from another location in the database.
Then, on the ticket screen, it will display like this:
Title: Traffic Ticket. Below the title, there will be:
The ticket title in the database, and when you press “I” for information, it will show all the other information from the database.
What did you understand?
It jumps directly to execution, and only after changing everything you requested will it tell you what it understood.
This is terrible for confirming something before changing it.