OpenAI Codex
✓Cloud coding agent with GPT-5.5 frontier model, 1M+ developers, Desktop App, in-app browser use, and parallel sandboxed environments
AI Coding CLIFreemium
OpenAI Codex is a cloud-based software engineering agent platform used by over 1M developers. Launched in May 2025 with a Desktop App added in February 2026, Codex spins up parallel sandboxed environments, reads your codebase, writes code, runs tests, and submits PRs autonomously. As of April 2026, GPT-5.5 — OpenAI's newest frontier model — is available in Codex and recommended for most tasks including complex coding, refactors, debugging, testing, validation, and knowledge-work artifacts. The Codex app added in-app browser use for local development servers and file-backed pages (visual bug reproduction and fix verification) and automatic approval reviews via a reviewer agent. Codex CLI 0.124.0/0.125.0 added quick reasoning controls, reasoning-token usage in `codex exec --json`, and Fast service tier defaults for eligible ChatGPT plans. The platform also includes a macOS Desktop App with Xcode integration for Apple developers.
- ●GPT-5.5 (April 2026): newest frontier model, recommended default in Codex for complex coding, refactors, debugging, testing, validation, and knowledge-work artifacts
- ●1M+ developers using Codex for software engineering
- ●Parallel sandboxed environments: reads codebase, writes code, runs tests, submits PRs
