Start a Live Activity

Up to five concurrent activities per device, including interactive activities. Distinct keys coexist. An active key owned by this requester conflicts unless replace is true; replacement affects only that key. Device capacity returns 422 ACTIVITY_CAPACITY_EXCEEDED with limit: 5. Suggested visible-character budgets, not guaranteed fit or API hard limits: proportional glyphs, device width and accessibility text size change fit. 0 means hidden. Expanded and Lock Screen subtitle replaces status on line 2; compact and small banners retain status. Omitted subtitle uses status. Overflow shares the two-line detail area with explicit detail. Compact percentage takes precedence over status when progress is supplied; terminal shows percentage or its prompt icon and never status. Expanded budgets (title/line 2/detail): standard 32/36/100; ring 32/30/80; hero 24/36/100; terminal 36/40/100; steps 32/36/100. Compact title/subtitle/detail are hidden; status budget is 8 without progress, except terminal 0.