Apple switched OS numbering from literal versions to a year-based naming/numbering scheme for all Apple OSes.
Apple changed its version numbering convention from version numbering with iOS 18 and iPadOS 18 to year-based versioning with iOS 26 and iPadOS 26. As explained on Wikipedia; bold emphasis is mine:
iOS 26 is the nineteenth and the current major release of Apple’s iOS operating system for the iPhone. It was announced on June 9, 2025, at the 2025 Worldwide Developers Conference (WWDC), and released on September 15, 2025.
It is the direct successor to iOS 18; its version number was brought forward to 26 as Apple changed its version numbering convention for consistency across its operating systems.
This change was done across all Apple OSes as explained on Engadget (June 9, 2025); bold emphasis is mine:
As part of an overhaul to its operating systems, Apple is making one of the most significant changes ever to its OS branding, the company announced at its WWDC 25 developer’s conference. Starting in 2026, it will shift from the current version numbers (macOS 15, iOS 18, iPadOS 18.5, etc.) to a year-based system across its entire OS lineup. As such, the names will change to iOS 26, iPadOS 26, MacOS Tahoe 26, WatchOS 26, TVOS 26, and VisionOS 26 and follow that pattern going forward.
