Codex

Two ways in

Development path

Form factor：coding-agent

1. 2021-08-10OpenAI Codex is released

   OpenAI releases Codex, a code-tuned model powering Copilot.

   https://openai.com/index/openai-codex/
2. 2025-04-16OpenAI Codex CLI open-sources a coding agent into the terminal

   On April 16, 2025 OpenAI open-sources Codex CLI: a lightweight coding agent that runs in your local terminal, able to read the codebase, edit files, run commands and propose pull requests.

   https://developers.openai.com/codex/cli
3. 2025-05-16Codex cloud agent: asynchronous, parallel software engineering

   OpenAI launches Codex, a research preview of a cloud-based software-engineering agent: each task runs in its own sandboxed environment, in parallel — writing features, answering codebase questions, fixing bugs, proposing pull requests — powered by codex-1, trained with reinforcement learning.

   https://openai.com/index/introducing-codex/
4. 2021-07-07HumanEval and pass@k: the first yardstick for code generationrelated

   OpenAI's Codex paper releases HumanEval — 164 "write a function from a docstring" problems scored by pass@k, the probability that at least one of k samples passes the unit tests.

   https://arxiv.org/abs/2107.03374

Solid dots mark events whose subject is this tool; hollow dots mark events that mention it. All entries come from this site's timeline, where every event carries a reachable source.

First release: not stated. Not derived automatically. The earliest timeline event mentioning this tool may be a version milestone, a different product with the same name, or a passing mention rather than a launch; each needs checking against an official source, so this is left empty.

Our articles about Codex

• The AI Coding Tools Map: Recognize the Form Factor First, Memorize Names Later

  Cursor, Trae, Claude Code, Codex, OpenClaw, Hermes Agent, DeepSeek Harness, WorkBuddy and Doubao Work sorted into three categories by form factor: IDE-embedded, terminal agent, and orchestration platform. For each category: what it gives you, how much control and visibility it takes away, and how people actually mix them in practice — so you can decide which category your first tool should come from.

  2026-09-30 · 13 min
• The Evolution of the Harness: Six Eras, Each With Its New Capabilities and New Ways to Crash

  From pure-prompt chatbots, CoT and ReAct reasoning prompts, and function calling — the real turning point — to MCP standardization, long-running CLI Agents, and always-on multi-Agent orchestration: era by era, what new capability the harness gained each time, and what new failure mode that capability incidentally introduced.

  2026-09-30 · 12 min
• What Codex Is: OpenAI's Coding Agent, on Two Legs — Local and Cloud

  The four forms hiding under the name Codex: the open-source Codex CLI (running in your terminal), the IDE extension, the desktop app, and Codex Web which runs tasks in parallel in the cloud. Covers installation, sign-in and billing models, sandboxing and approval mechanics, and how its form factor differs from Claude Code.

  2026-09-30 · 9 min
• Installing the OpenAI Codex CLI: Sign-In, Permissions, and Your First Task

  OpenAI's terminal coding agent Codex CLI, from system requirements, three official installation methods, ChatGPT-account sign-in and API-key sign-in, to the three /permissions presets and non-interactive mode. Every step spells out the output you should see and flags which commands I could not verify against the official documentation.

  2026-09-30 · 22 min

Tools it is often compared with

• CodexvsClaude Code
• CodexvsCursor
• CodexvsGitHub Copilot
• CodexvsDevin

Alternatives