Apple iOS 8.0 (2014)

iOS 8 incorporated significant changes to the operating system. It introduced a programming interface for communication between apps and "Continuity", a cross-platform (Mac, iPhone, and iPad) system that enables communication between devices in different product categories, such as the ability to answer calls and reply to SMS on the Mac and iPad.

Continuity includes a "Handoff" feature that lets users start a task on one device and continue on another. Other changes included a new Spotlight Suggestions search results feature that provides more detailed results, Family Sharing, where a family can link together their accounts to share content, with one parent as the administrator with permission controls, an updated keyboard with QuickType, providing contextual predictive word suggestions and Extensibility, which allows for easier sharing of content between apps. Third-party developers got additional features to integrate their apps deeper into the operating system, including support for widgets in the Notification Center, and the ability to make keyboards that users can replace the default iOS keyboard with.

App updates in the release included the new Health app, which can aggregate data from different fitness apps, as well as enabling a Medical ID accessible on the lock screen for emergencies, support for iCloud Photo Library in the Photos app, which enables photos to be synchronized and stored in the cloud, and iCloud Drive, which lets users store files in the cloud and browse them across devices. In iOS 8.4, Apple updated its Music app with a streaming service called Apple Music, and a 24-hour radio station called Apple Music 1.

Reception of iOS 8 was positive. Critics praised Continuity and Extensibility as major features enabling easier control and interaction between different apps and devices. They also liked the QuickType keyboard word suggestions, and highlighted Spotlight Suggestions for making the iPhone "almost a portable search portal for everything.” However, reviewers noted that the full potential for iOS 8 would only be realized once third-party developers integrated their apps to support new features, particularly widgets in the Notification Center.

Roughly a week after release, iOS 8 had reached 46% of iOS usage share. In October 2014, it was reported that the adoption rate had "stalled,” only increasing by "a single percentage point" from the previous month. This situation was blamed on the requirement of a high amount of free storage space to install the upgrade, especially difficult for iPhones sold with 8 or 16 gigabytes of maximum storage space. The following December, iOS 8 had reached 63% usage share, a notable 16% increase from the October measurement.