Originally published at https://aicoding-guide.com . Codex feels slow, or it overthinks a trivial fix. The knob for that is reasoning effort , the Codex counterpart of extended thinking in Claude Code, controlled by the model_reasoning_effort key. In short: set model_reasoning_effort = "high" (or another value) in ~/.codex/config.toml to change it permanently, use the -c flag for a single run, or /model during a session. The five levels are minimal , low , medium , high , ...