Yes, in clojure you need to require a namespace before using its vars

If I just create a new empty ns without any require and run the code , it just runs and changes the global var from that library. Is this expected?

you can use qualified vars without requiring the namespace but only if the corresponding namespace was loaded (for example requered transitively). but it is always better to be explicit and require in the namespace that uses that var

Thanks for the explanation. I do have a http client which has a {:as :json} which requires cheshire transitively I guess. Is there a way to list all namespaces being required transitively so I can verify this case?

You can use :verbose with require https://clojuredocs.org/clojure.core/require

Ahh, thanks again! I can see where it's loaded now. Much appreciated!