Vuex works like this: you actually mutate the state instead of creating a new one as it's expected with Redux. But this mutation takes place is a single, controlled place (in the store mutation functions), so you get the benefit of centralising the state management code and avoid the cumbersome immutable transformations patterns which Redux requires.

That said, after having worked with Vuex, I much prefer the immutable newState = f(oldState) pattern used with Redux.