Floors at the 26 releases

Status: accepted, 2026-10-02. Serves The store is the UI's state. Reopen when an adopter needs an older release, or at the 1.0 review.

Context#

Observation, which the store is built on, needs iOS 17. Every release since added something the runtime would otherwise have to work around: Mutex and the main-actor View baseline in 18, Observations and InlineArray in 26, continuous observation in 27.

Decision#

iOS 26, macOS 26 and the matching 26 releases of the other Apple platforms; Swift 6.2 tools (Xcode 26 or later); Swift 6 language mode. The runtime carries no availability branches below the floor; iOS 27 APIs are used behind a check where they pay.

Evidence#

• iOS 26 and 27 together were about 91% of iPhones in late September 2026 (TelemetryDeck), with iOS 17 and older under 2%.
• The App Store has required the iOS 26 SDK since April 2026, so every shipping app already builds with the tools the floor assumes.
• The owner's products do not need older releases, and backward compatibility was explicitly not a concern.

Not chosen#

• iOS 17, the hard floor of Observation: every newer convenience behind a check, for under 2% of devices.
• iOS 18: Observations and InlineArray behind checks, for under 10%.