The Short Version
watchOS 26 added hypertension detection to Apple Watch Series 9, 10, 11, and Ultra 2 and 3, needing a 30-day baseline and an iPhone 11 running iOS 26, for users 22 and older.
Samsung got FDA clearance for blood pressure monitoring first, so Apple is playing catch-up here. But Apple's hypertension alerts work on older Apple Watch models, meaning millions of people already wearing one get the feature for free. No new watch required. That's a win for existing owners, even if Apple didn't lead the race.