OpenAI’s May Codex update adds skills to the composer’s @ menu, so a skill can be inserted inline alongside files and other mentions instead of being invoked through a separate path. The bundled OpenAI Docs skill was also refreshed for GPT-5.5 and gpt-image-2. On its own this is a minor ergonomics change. In context it marks something larger.

The format, not the feature

A skill is a SKILL.md file that packages instructions, resources, and optional scripts so an agent follows a workflow the same way every time. Skills launched for Codex in December 2025. What changed by May 2026 is reach: the same SKILL.md format is now honored by Claude Code, Codex CLI, Gemini CLI, GitHub Copilot (through VS Code agent skills), Cursor (with manual placement), and community tools including Cline, Windsurf, and OpenCode.

Why it matters

A skill written once is now portable across most major agents. That weakens a real source of lock-in: the workflow knowledge a team encodes for one tool no longer has to be rewritten when it switches tools or adds a second one. For organizations running a mixed stack — some engineers on Claude Code, others on Codex or Copilot — a single shared skill library now covers all of them instead of fragmenting per vendor.

The standardization is early and the edges still differ. Script execution, resource paths, and skill placement are not uniform across tools, so a skill that exercises those features still needs per-tool testing. The convergence is on the core format, not yet on the full surface — but a shared format is the part that matters for portability, and that part has effectively settled.

For the portable subset and a worked example, see Writing a SKILL.md that works across Claude Code, Codex, and more.