OpenAI hasn't said a word about GPT-5.5, but the model name just popped up in its Codex developer tool.
GPT-5.5 is now listed at the very top of the model selector dropdown in OpenAI Codex.
Select it and try to submit a request, though, and Codex throws a 400 error: "The 'gpt-5.5' model is not supported when using Codex with a ChatGPT account." The model is currently unavailable. OpenAI has yet to release any official announcement or documentation about GPT-5.5.
Multiple outlets previously reported that OpenAI's next-generation frontier model, internally codenamed "Spud," finished pre-training at the end of March. The outside consensus is that its official name will be either GPT-5.5 or GPT-6, with a release expected in the second quarter. This quiet appearance in Codex follows a recent pattern of specialized model rollouts, like the release of GPT-5.4-Cyber for cybersecurity professionals.