Get activist stakes (SEC Schedule 13D: holders of more than 5% of a class of shares with intent to influence control), one row per reporting person. Query by ticker (who holds activist stakes in this company) or by filer_cik (what stakes does this activist hold); provide exactly one of the two. By default each stake's current state is returned; set history=true for the full amendment chain. This endpoint is the activist-only view of /beneficial-ownership.