Run Codex and Claude Code Together, Cheaply
Why run Codex and Claude Code side by side?
Using two coding assistants on the same task is not about redundancy; it is about getting better output faster. Codex can be strong at implementation detail and structured edits, while Claude Code often shines at broad reasoning, file-aware refactors, and explaining tradeoffs. When you run them side by side, you can compare plans, spot edge cases, and choose the best patch before it reaches production.
The key is keeping the workflow cheap enough that you can do it every day. That is where 59API fits well. It is an AI API relay with pay-as-you-go pricing, native official-quality models, and compatibility with Claude Code, Codex, and any OpenAI SDK. In practice, that means you can use the models you already want without paying premium platform overhead.
Step 1: Pick one real task
Do not start with a toy prompt. Choose a task that is meaningful but bounded, such as:
- Adding a new API endpoint
- Refactoring a legacy utility into smaller functions
- Writing tests for a flaky module
- Fixing a bug with a reproducible failing case
Create a branch, open the relevant files, and write down the acceptance criteria before you ask either model for help. The more specific your goal, the easier it is to compare the two outputs fairly.
Step 2: Connect both tools to 59API
Use https://api.59api.com as the base URL in the client configuration for each tool. Point your API key to 59API, then choose the model you want for the job. For example, use Claude models such as Opus, Sonnet, Haiku, or Fable when you want to compare Claude Code behavior, and use GPT-based models when you want Codex-style output. Because 59API supports the same official-quality models without downgrade, you are evaluating real model behavior, not a watered-down proxy.
If your setup supports custom endpoints, configure both tools against the same relay. That gives you a clean apples-to-apples comparison and keeps your billing simple.
Step 3: Give both assistants the same brief
Ask each tool to work from the same instructions. Include:
- The exact files or folders to inspect
- The desired behavior change
- Constraints like style, performance, or backwards compatibility
- Testing expectations, such as unit tests or snapshot updates
A good prompt might say: “Inspect the auth middleware, propose the smallest safe change, update tests, and explain any risks before editing.” Then run the same request in Codex and Claude Code. If one model proposes a cleaner abstraction and the other gives a tighter patch, you can combine the best parts.
Step 4: Run them in parallel, not in sequence
Open two terminals or split your editor into two panes. Let each assistant generate a plan first. Review the plans before you let either one write files. This saves time because you can reject bad assumptions early.
In many teams, the best pattern is:
- Claude Code drafts the architecture or refactor plan
- Codex implements the concrete code changes
- You review both, then ask one model to reconcile differences
This is especially useful for production work where you need clarity on failure modes, migrations, and rollback steps.
Step 5: Compare outputs like a reviewer
Do not ask which answer is “better” in the abstract. Compare them on practical criteria:
- Does it preserve existing behavior?
- Are tests included and meaningful?
- Is the code minimal or over-engineered?
- Does it explain tradeoffs clearly?
Then run the test suite, lint, and a local smoke test. If both assistants agree, great. If they disagree, inspect the disagreement itself; that is often where the hidden bug lives.
Step 6: Move to production with cost control
Once the patch is stable, keep the workflow lean. Use cheaper models for routine edits, save larger models for architecture and tricky debugging, and monitor token usage per task. Because 59API is pay-as-you-go and among the cheapest relays, you can afford to use it as part of your normal development loop instead of reserving it for emergencies.
If you are working across a team, the referral rebate can lower costs further. That matters when you are running repeated experiments, maintaining multiple branches, or using AI for code review on a daily basis.
A simple production-ready habit
For every non-trivial change, ask both Codex and Claude Code for the same three things: a plan, an implementation, and a risk summary. Then merge the strongest version of each. With 59API in the middle, you get a low-cost, model-flexible setup that stays close to official-quality behavior and works with your existing tools.
If you want to try this workflow without overcommitting to a pricey platform, sign up for 59API, connect your clients to https://api.59api.com, and run your next feature branch through both assistants side by side.