No, v3 is a release with breaking changes:

This release includes several breaking changes; read the full migration guide here. It’s worth mentioning that many of the breaking changes are updates to API endpoints and only affect third-party tools that integrate with Immich’s API. For the vast majority of users, updating works exactly as it always has.

https://immich.app/blog/v3.0.0-release

That’s why the major version was increased, it implies breaking changes in semantic versioning, which Immich is doing since v2 apparently:

Given a version number MAJOR.MINOR.PATCH, increment the:

1. MAJOR version when you make incompatible API changes
2. MINOR version when you add functionality in a backward compatible manner
3. PATCH version when you make backward compatible bug fixes

https://semver.org/