iOS 26 and iPadOS 26 updates will be more generous in terms of device support compared to macOS 26 Tahoe release by Apple.
Only iPhone XR, XS, and 7th-generation iPad will not be able to run iOS 26 and iPadOS 26, while other devices supporting iOS and iPadOS 18 will be able to upgrade.
Apple does not provide explicit reasoning for dropping support for certain devices but it is usually due to a combination of age and technical capability.
The 7th-gen iPad, for instance, was using a 2017-vintage Apple A10X chip despite being introduced later.