Simon Willison’s Weblog

If you've been experimenting with OpenAI's Codex CLI and have been frustrated that it's not possible to select text and copy it to the clipboard, at least when running in the Mac terminal (I genuinely didn't know it was possible to build a terminal app that disabled copy and paste) you should know that they fixed that in this issue last week.

The new 0.20.0 version from three days ago also completely removes the old TypeScript codebase in favor of Rust. Even installations via NPM now get the Rust version.

I originally installed Codex via Homebrew, so I had to run this command to get the updated version:

brew upgrade codex

Another Codex tip: to use GPT-5 (or any other specific OpenAI model) you can run it like this:

export OPENAI_DEFAULT_MODEL="gpt-5"
codex

This no longer works, see update below.

I've been using a codex-5 script on my PATH containing this, because sometimes I like to live dangerously!

#!/usr/bin/env zsh
# Usage: codex-5 [additional args passed to `codex`]
export OPENAI_DEFAULT_MODEL="gpt-5"
exec codex --dangerously-bypass-approvals-and-sandbox "$@"

Update: It looks like GPT-5 is the default model in v0.20.0 already.

Also the environment variable I was using no longer does anything, it was removed in this commit (I used Codex Web to help figure that out). You can use the -m model_id command-line option instead.