Schedule 13D
Also called: 13D, 13G, beneficial ownership report
A Schedule 13D must be filed within days of acquiring more than 5% of a company's shares with an intent to influence control — which is why it's the public starting gun for an activist campaign. Passive holders file the lighter 13G instead. The filing window was shortened in 2023, narrowing the period in which an activist could quietly accumulate before disclosing.