iOS 9 is the ninth major release of iOS, released on September 16, 2015, ahead of the iPhone 6s and iPhone 6s Plus. After two feature-dense, bug-prone cycles, it was deliberately a consolidation year — stability, performance, and battery led the pitch — and it made the point concretely by dropping no devices at all: everything that ran iOS 8, back to 2011's iPhone 4s, ran iOS 9, with the update itself slimmed from 4.6 GB to 1.3 GB so 16 GB devices could actually install it.

Its additions aimed at intelligence and the iPad: Proactive suggestions surfaced apps, contacts, and events before being asked, while Slide Over, Split View, and Picture in Picture gave the iPad true multitasking — the beginning of its productivity turn.

The Proactive layer (contextual Siri and Spotlight suggestions), a redesigned app-switcher, the News app, a rebuilt Notes with sketching and attachments, transit directions in Maps, Low Power Mode (extending battery roughly an hour), the back-to-previous-app breadcrumb, six-digit passcodes as default, and content-blocker support in Safari. The system font changed from Helvetica Neue to Apple's own San Francisco. iOS 9.3 added Night Shift's blue-light scheduling.

Every iOS 8 device: iPhone 6s/6s Plus and iPhone SE (added at its 2016 launch) down through iPhone 4s, iPad 2 and later, and the fifth/sixth-generation iPod touch. The final release, 9.3.6, arrived in July 2019 — a GPS-week-rollover fix shipped to eight-year-old hardware.

iOS 9 proved the "tick-tock" release rhythm — expansion, then consolidation — that Apple returned to with iOS 12, and its zero-drop support table became the marketing benchmark for platform longevity. San Francisco became the company-wide typeface (including the lettering this wiki's Apple-style infoboxes reference), the iPad multitasking model matured into iPadOS, and Proactive's quiet suggestion layer was the platform's first step down the path that leads to Apple Intelligence.