Did Codex Just Replace ChatGPT Inside OpenAI’s Own Workflows?

A new OpenAI study finds its Codex agent now generates 99.8% of the output tokens the company's employees produce, signaling that autonomous AI has overtaken chatbots at work.

Key Points:

Codex Overtakes ChatGPT Internally

Researchers from OpenAI, Columbia Business School, the Wharton School, and Duke University published the paper on Jun. 25, drawing on usage across individual subscribers, outside organizations, and the company's own staff. The work spread quickly because it grounds a much-hyped shift in measured behavior rather than forecasts.

It separates two modes of use, treating chat as conversation and Codex as delegated action that can inspect files and run commands.

Inside OpenAI, Codex has largely replaced business use of ChatGPT, and in the week before Jun. 11 some 60.3% of its sessions called an outside tool, against 21.9% for the chatbot. Outside the company the split stays wide, as Codex accounts for 63.3% of output tokens at organizations and just 16.5% among individuals.

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Non-Developers Drive The Boom

The sharpest growth came from workers far outside engineering, where use once sat near zero. Non-developer adoption climbed 137 times among individuals and 189 times at organizations in the ten months since August 2025. Legal, finance, and recruiting teams at the company reached majority Codex use by April 2026, months behind the engineers who moved first and set the early pattern.

Task complexity rose in step with that spread. The share of individuals handing over jobs estimated to need more than eight hours of human effort hit 25.6%, up from 2.1% in December 2025, while most now delegate work worth at least half an hour.

More than one in ten users run three or more agents at once each week.

Agentic AI Redraws Work

Productivity climbed with the change, as median output per OpenAI worker rose at least tenfold across roles since November 2025, reaching 13 times for lawyers and more than 50 times for researchers.

The authors caution that OpenAI is an unusually easy home for agents, with deep training and no cost limits, so its figures overstate the typical firm. Even so, they argue the internal shift previews where wider adoption is heading, with human value moving toward setting tasks, checking output, and steering several agents at once.

OpenAI released Codex in April 2025 as a tool built narrowly for software developers. ChatGPT stayed the company's default for months, until engineers drifted toward the agent and weekly active users grew more than fivefold over the first half of 2026, passing five million a week.

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