Run a large code migration with parallel Codex agents
Give Codex a short, clear prompt and let several agents work on separate copies of the code while an engineer reviews every proposed change.
Oct 25, 2026
Migrate [component or test files] from [old framework] to [new framework]. Keep behavior identical, keep tests passing, and work one file at a time. Open a change for each file with a short summary of what changed.
How to use it
1. Define the migration goal in a short, simple prompt 2. Set up Codex with access to the repository 3. Run several agents in parallel, each on a separate copy of the codebase 4. Check progress at set times each day 5. Review and approve every proposed change 6. Run the full test suite before merging
Result
Migration done in about 2 weeks for about $12K in model costs vs an estimated $6M manual effort. Example: Input: "Replace Enzyme tests with React Testing Library in /src/components". Output: a series of reviewed pull requests, one per file.
Tips and gotchas
Human review: Engineer reviewed every change. Pitfall: Simple instructions worked better than elaborate setups. Best for: Engineering leads, senior developers (Advanced). Time saved basis: Sourced.
openai.com
https://openai.com/index/asana/