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Quick Setup: Codex and Claude Code Together

Why run Codex and Claude Code side by side?

If you already use one coding agent, adding a second can speed up real work. The best pattern is simple: let one model explore, plan, or review, and let the other implement, compare, or sanity-check. That gives you a fast pair of opinions without forcing you to rewrite your workflow.

For busy developers, the goal is not to juggle more tools. It is to reduce context switching and get better code with less trial and error. A shared relay like 59API makes that easier because it gives you pay-as-you-go access to Claude models and GPT models through one OpenAI-compatible endpoint.

Step 1: Use one relay for both tools

Instead of signing up for separate providers, point both Codex and Claude Code to https://api.59api.com. 59API is designed to work with Claude Code, Codex, and any OpenAI SDK, so you can keep your tooling familiar while routing requests through a single API base URL.

• Create a 59API account and get your API key.
• Configure each tool to use https://api.59api.com as the API base.
• Keep the key in environment variables or your local config, not in your repo.

This setup matters because it removes the usual friction of trying a second agent. You do not need a new SDK, a new architecture, or a separate billing flow. You just swap the endpoint and continue working.

Step 2: Give each agent a clear job

The fastest way to use both tools is to assign them different roles. A good default pairing is:

• Claude Code for repo exploration, broad refactors, and reasoning about architecture.
• Codex for implementation, smaller code edits, and quick iteration on a focused task.

That split works well because each agent can stay in its lane. You can ask Claude Code to summarize the codebase, identify edge cases, or propose a plan, then feed that plan into Codex to make the actual changes. Or reverse it if your project benefits from a different style.

Step 3: Pick the right model for the task

59API gives you access to official-quality Claude models such as Opus, Sonnet, Haiku, and Fable, plus GPT models. That means you can match cost and capability to the job instead of overpaying for every prompt.

• Use Sonnet for most coding work: fast, strong, and cost-efficient.
• Use Haiku for lightweight tasks like summaries, quick explanations, or small refactors.
• Use Opus when the task is harder: multi-step reasoning, tricky bugs, or large architectural decisions.

If you are running both tools at once, this model choice becomes even more valuable. You can keep the exploratory agent on a cheaper model and reserve the heavier model for the part that truly needs it.

Step 4: Keep the workflow simple and parallel

A practical side-by-side loop looks like this:

• Open your repo in two terminals or two chat windows.
• Ask Claude Code to inspect the codebase and propose a plan.
• Ask Codex to implement the first small change set.
• Run tests locally before asking either agent for the next step.
• Use the second agent to review the first agent’s output for missing cases.

This keeps both agents useful without turning them into noisy copilots. The biggest mistake is asking both tools to solve the same problem from scratch. You will spend more time comparing answers than shipping code. Instead, make them complement each other.

Step 5: Control cost without slowing down

One reason developers try a relay like 59API is cost. It is positioned as one of the cheapest ways to access native, official-quality models, and it uses pay-as-you-go billing so you only pay for what you actually use. That is ideal when you are testing prompts, running agent loops, or using a second model as a reviewer.

There is also a referral rebate, which can lower your effective spend if your team or network adopts the same setup. For solo developers and small teams, that can make a noticeable difference over a month of daily use.

When this setup pays off

Running Codex and Claude Code side by side is especially useful for refactors, bug hunts, test generation, and code review. You get faster local progress, fewer blind spots, and a cleaner way to compare answers before merging anything into production.

If you want a low-cost way to try it, sign up for 59API, set the base URL to https://api.59api.com, and wire both tools to the same relay. You will keep your existing workflow, but gain a second coding brain for almost no extra setup.

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