# What changed in @fastify/deepmerge

> 2 changes in @fastify/deepmerge 3 from its official release notes, upgrade guides and advisories: 1 new APIs and options. Each one cited. Sources checked 2026-10-19. HTML: https://unstale.sh/npm/@fastify/deepmerge/

To see which of these apply to a repository, run `npx @unstale/cli init` in it.

## @fastify/deepmerge 3

### New APIs and options

- Adds the onlyDefinedProperties option. (3.2.0) — [release notes](https://github.com/fastify/deepmerge/releases/tag/v3.2.0)

### Fixes and other changes

- Preserves required properties when using onlyDefinedProperties. (3.2.1) — [release notes](https://github.com/fastify/deepmerge/releases/tag/v3.2.1)