ChatGPT and Codex are two OpenAI products built on the same family of GPT models but aimed at different tasks. ChatGPT is a conversational assistant, available through web, desktop, and mobile apps, that answers questions and produces text, code, and analysis, with optional tools such as web browsing, file analysis, and code execution. Codex is an agentic coding tool for software engineering tasks such as writing code and fixing bugs, relaunched in April 2025 as an open-source CLI that runs locally in the terminal. Wikipedia
Codex has since expanded to a cloud-based service, IDE extensions, and a desktop app released in February 2026, and its current generation runs on GPT-5.5, with terminal, IDE, and web surfaces sharing one execution model. In practice, ChatGPT is used for interactive explanation and drafting, while Codex is delegated multi-step work inside a repository: reading the codebase, editing files, running tests, and preparing pull requests. Both are accessible under ChatGPT subscription plans and, for Codex, through the OpenAI API with usage-based billing.