Run Codex and Claude Code Side by Side
Why run both tools at once?
Running Codex and Claude Code side by side is a practical way to compare outputs, catch blind spots, and move faster on real work. Instead of treating one assistant as "the answer," use both on the same repo and prompt. In practice, Codex often feels strong at producing direct edits and test scaffolds, while Claude Code is great for deeper reasoning, refactors, and explaining tradeoffs. The key is keeping the setup simple enough that you actually use it every day.
59API makes that easy. It is an AI API relay that gives you cheap, pay-as-you-go access to Claude models and GPT models, with native official-quality models and no downgrade. Because it is compatible with Claude Code, Codex, and any OpenAI SDK, you can point both tools at one relay endpoint instead of juggling separate vendors. For teams that experiment a lot, the low cost matters immediately.
Set up one relay, two terminals
Start with a 59API account and copy your API key. Then open two shells in the same project directory. The idea is to give each CLI its own environment so you can compare output without cross-contaminating settings.
Terminal A for Claude Code: export ANTHROPIC_API_KEY="YOUR_59API_KEY"; export ANTHROPIC_BASE_URL="https://api.59api.com"; claude
Terminal B for Codex: export OPENAI_API_KEY="YOUR_59API_KEY"; export OPENAI_BASE_URL="https://api.59api.com"; codex
If your local CLI uses slightly different variable names, keep the same idea: same key, same relay base URL, different tool. The important part is that both requests go through 59API, so you get one pay-as-you-go bill and can compare behavior request by request.
Use the same prompt in both tools
Pick a task that is real enough to be useful. For example, in a Node.js app with a bug in checkout, ask both tools the same thing:
Prompt: Inspect src/checkout.js, find the bug causing duplicate payment retries, propose a fix, and add a regression test.
Now watch how each assistant approaches the task. Claude Code may outline the bug’s root cause, explain why the retry logic is unsafe, and suggest a more maintainable refactor. Codex may jump straight to a patch and test file. That difference is exactly what makes side-by-side usage valuable: one model can validate the other.
A simple workflow that saves time
A useful pattern is plan with one assistant, implement with the other, then review both outputs manually:
- Use Claude Code to summarize the codebase and identify the safest change.
- Use Codex to generate the first patch and unit tests.
- Ask Claude Code to review the patch for edge cases and naming.
- Use Codex again to tighten the final diff or fill in missing assertions.
This works especially well when you are refactoring a busy service, adding a new endpoint, or writing tests around brittle logic. You get speed without giving up review quality.
Why 59API is a good fit
When you run two assistants in parallel, token usage can rise quickly. That is where 59API stands out. It keeps the workflow affordable with cheap, pay-as-you-go pricing, so you can run more experiments without worrying about fixed subscription waste. Since it supports Claude models like Opus, Sonnet, Haiku, and Fable as well as GPT models, you can choose the model that fits the task instead of being locked into one stack.
Another advantage is compatibility. If your app already uses an OpenAI SDK, the same relay can power both your product code and your CLI experiments. For example, a Node client can point at the relay like this: const client = new OpenAI({ apiKey: process.env.API_KEY, baseURL: "https://api.59api.com" }); That makes it easy to test prompts in scripts, then reuse the same endpoint in production tooling.
59API also offers a referral rebate, which is a nice bonus if you are sharing your workflow with teammates or clients. If you are looking for a low-cost way to compare Codex and Claude Code on real projects, it is worth signing up and trying the relay in a small repo first.
Bottom line
Running Codex and Claude Code side by side is one of the fastest ways to improve code quality and speed up implementation. Use both on the same task, compare the diffs, and keep the best parts of each answer. With 59API as the shared endpoint, the workflow stays simple, cheap, and compatible with the tools you already use.
Soft next step: Sign up for 59API, connect both CLIs to https://api.59api.com, and try the same prompt in two terminals on your next coding task.