OpenAI ships o3, o4-mini, and the Codex CLI coding agent

OpenAI released its o3 and o4-mini reasoning models on 16 April 2025 together with Codex CLI, an open-source coding agent that runs in a developer’s terminal, reads and edits project files, runs shell commands, and connects to external tools through the Model Context Protocol.

Why it mattered It brought OpenAI’s reasoning line into general availability and put a terminal agent directly against Anthropic’s Claude Code, released eight weeks earlier.