Switch Between Claude Code and Codex in One Project

Switching between Claude Code and Codex can be useful when you want a second opinion, a different implementation approach, or a fresh review. The difficult part is not opening another tool. It is preserving the decisions that matter without paying to explain the entire project again. This walkthrough uses one project, sequential editing, and a short written handoff.

Choose a small task and record a clean starting point

Start with a task you can verify independently, such as fixing a validation bug or adding a modest interface improvement. Write down the expected behavior, what must remain unchanged, and how you will check the result. A narrow task makes both the handoff and the final review cheaper.

Before either assistant edits anything, inspect your existing changes and save a version-control checkpoint. Keep unrelated work separate. If the first assistant takes an unhelpful direction, you should be able to identify its changes without untangling yesterday's unfinished work.

Connect each tool without assuming settings are interchangeable

Claude Code and Codex have separate connection settings. Sharing a project does not mean they share authentication, provider configuration, or conversation history. Follow the current setup instructions for each tool and confirm that your installed version supports the connection method you intend to use.

MyRelay works with both tools and gives an individual developer one key and one pay-as-you-go budget across supported providers. If you want that shared billing view, create a MyRelay account before connecting the tools. Use the service's current tool-specific instructions rather than copying settings from one client into the other.

Keep credentials out of project notes and version control. Make one small request from each tool, then check that the requests appear in your MyRelay usage records. This confirms the connection before you send substantial project context. Shared billing still does not make the two tools' sessions interchangeable.

Give the first assistant a bounded assignment

Open the project in Claude Code and describe the task, its constraints, and your acceptance checks. Ask it to inspect only the relevant areas first and propose a short plan before making changes. Review that plan, especially any suggestion to add dependencies or broaden the task.

Then allow a limited implementation. Keep approval requirements appropriate to the project, particularly for destructive actions or access to sensitive information. Avoid asking for implementation, broad refactoring, documentation cleanup, and an architectural review in one request. Those extra goals increase both the change surface and the context bill.

Write a handoff that captures decisions, not the whole chat

Before switching, ask Claude Code to summarize the work for another assistant. Review the summary yourself and keep it in a short project note or copy it into the next session. A useful handoff contains complete statements about:

• The requested behavior and the constraints that still apply.
• The changes already made and the reason for the chosen approach.
• The checks performed, their results, and anything not yet verified.
• The remaining question or next action for the second assistant.

Do not transfer the entire conversation by default. Long transcripts can carry stale assumptions and consume tokens without improving the next decision. The handoff should direct Codex toward relevant evidence in the project, not replace its inspection of that evidence.

Let Codex review before it makes further edits

Stop the first assistant's editing activity before starting Codex in the same working copy. Give Codex the handoff and ask it to inspect the existing changes against the original acceptance checks. Make clear that it should preserve unrelated work and report concerns before rewriting anything.

If it identifies a concrete problem, authorize a focused correction. If it merely prefers another style, weigh that preference against the cost and risk of another revision. Switching tools is most valuable when it answers a specific unresolved question, not when it starts an endless cycle of competing rewrites.

Verify the result and compare the actual spending

Run the relevant tests and inspect the final changes yourself. Neither assistant's confidence is a substitute for verification. Save a checkpoint once the result meets your acceptance checks.

Finally, review the requests, token counts, and costs in MyRelay. Compare the whole workflow, including repeated context and review requests, rather than treating a tool switch as an automatic saving. For the next task, keep the handoff details that helped and remove the ones that did not. A disciplined switch should leave you with clearer evidence and controlled spending.