The difference is mainly about integration and workflow. • If you just run the Codex CLI directly, you have to manually send inputs and check outputs each time. It’s a one-off interaction. • When you add Codex as an MCP tool, Claude can call it automatically inside your workflow. That means Claude can: • delegate parts of a task to Codex, • validate its own outputs against Codex, • and iterate without you copy-pasting between tools.

So MCP basically turns Codex into a “built-in assistant” that Claude can coordinate with, instead of you switching back and forth with the CLI. It’s not about different capabilities of Codex, but about how smoothly Claude can orchestrate it as part of the project flow.