---
id: expand
requestedLanguage: en
descriptionLanguage: en
---

# Parallel Change / Expand–Contract

- Type: migration technique
- Group: Evolving existing code
- Placement: Changing an existing system
- [Source](<https://martinfowler.com/bliki/ParallelChange.html>)

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Add a new interface → migrate consumers → remove the old interface.

## Relationships

- can be combined with: [Branch by Abstraction](/practices/abstraction/en.md) (combination)
- helps change APIs during: [API-first design](/practices/api/en.md) (support)
- helps preserve: [Backward Compatibility](/practices/compatibility/en.md) (support)
- helps carry out: [Database Change Management / Migrations](/practices/dbmigration/en.md) (support)

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