in API design thats a toss up.
Since you are talking to the users endpoint why duplicate the word “user” across the response since it’s obvious that the ID and Login returned by the users endpoint(s) are for a user.
Other none user end points, explicitly state it’s a user_id as otherwise id would be the stream id (for example in the case of a stream end point)
Ditto for database design, if it’s the users table, why call the column user_id when id fits perfectly. Other tables that reference the users id from the users table would say user_id