What is Codex?

Codex is an AI coding assistant developed by OpenAI. As of mid-2026, it has seen rapid adoption, with usage surging from near zero at the start of the year to mid single digits (percentage of users), and is being used by non-technical workers at three times the rate of developers.

• Oct 2025 - Sam Altman said Codex was moving from multi-hour to multi-day tasks, expected within the next year.
• May 2026 - Nathaniel Whittemore shared that Codex had gone from almost no users at the beginning of the year to mid single digits.
• Jun 2026 - Nathan Labenz said non-technical knowledge workers were adopting Codex at three times the rate of developers.
• Jun 2026 - Nathaniel Whittemore reported that OpenAI’s compaction system improvements allowed Codex to maintain persistent threads without losing context.
• Jul 2026 - Jason Lemkin noted that Replet’s sub-agent ‘the architect’ runs on Codex via OpenAI.
• Jul 2026 - Clay Bavor said top engineers leaning into Codex and similar tools were spending over $100,000 per year on tokens.