At what phase do you/one of your team members update the release version # of your software/application?

Currently, we have dev -> feature-branch -> dev -> release -> staging -> production branching system. Where do you think the versioning should be maintained as a part of source code?

I'd think that, version should be managed at release stage and could be merged in staging as well as dev once the release branch has all the necessary updates. But I am not convinced that it's a good approach.

Thoughts?