iOS 5 is the fifth major release of iOS, released on October 12, 2011, alongside the iPhone 4s — announced at the last WWDC keynote Steve Jobs attended, and shipped a week after his death. It cut the platform's final cord: "PC Free" setup, over-the-air updates, and iCloud sync and backup ended the requirement that every iPhone belong to a computer running iTunes, redefining the device as fully self-sufficient.

Its user-facing additions were among the era's stickiest: Notification Center replaced the interrupting blue alert boxes with a pull-down shade, iMessage folded a free Apple-to-Apple messaging network into the SMS app, and Siri — exclusive to the 4s — introduced the voice-assistant category to the mainstream.

Notification Center with lock-screen notifications, iMessage across iPhone/iPad/iPod touch, iCloud (mail, contacts, calendars, device backup, Photo Stream, Documents in the Cloud), Reminders with geofencing, Newsstand, Twitter system integration, lock-screen camera access with volume-button shutter, AirPlay Mirroring, and the split/thumb keyboard on iPad. Point releases delivered iTunes Match (5.0.1) and Japanese Siri (5.1).

The launch itself strained Apple's servers for days, and early 4s battery-drain bugs drew enough coverage that Apple issued a rare public acknowledgment before patching.

iPhone 4s, iPhone 4, iPhone 3GS, both iPads, and iPod touch 3rd/4th generations — dropping the iPhone 3G. The 3GS's inclusion continued its improbable software longevity.

iOS 5 is the hinge between the accessory era and the independent device: iCloud's activation-to-backup autonomy became the baseline expectation for every phone platform. iMessage grew into one of Apple's strongest lock-in assets (and antitrust exhibits), Notification Center's pull-down shade became a universal smartphone idiom, and Siri opened the assistant race that still runs — through iOS 27's Siri AI rebuild.