Reports have surfaced on Hacker News from users utilizing GPT-5.4xhigh sessions regarding ongoing errors.
Reports of Codex API Errors During GPT-5.4xhigh Sessions
This article is a translation. Read the Japanese original
The error is described as unexpected status 404 Not Found: Unknown error, with the URL identified as https://chatgpt.com/backend-api/codex/responses.
According to the reports, while sending and updating messages remains possible, this error occurs repeatedly when the agent attempts to think and continue its process. There are also reports of cases where the process fails even after five retries.
On the other hand, GPT-5.5xhigh sessions do not appear to be affected. Additionally, it was noted that the error occurs not immediately after compaction, but rather after approximately 50,000 tokens have passed since compaction.
The poster suggested the need for more error-tolerant retry logic using exponential backoff.
--- Source: Codex Is Down (Hacker News Frontpage, 2026-09-03)