iPhone SE (2nd generation)
The 2020 iPhone SE launched with iOS 13.4 installed, in between major iOS updates.
Apple emphasizes that the iPhone SE is designed to run the latest features in iOS 13, and will support iOS feature and security updates going forward.
iPhone SE (1st generation)
For the most part, Apple has released new iPhone models to coincide with major iOS updates. For example, the iPhone 6s launch was synchronized with the release of iOS 9.0 in September 2015.
Newest iPhone FAQs
Adding a 4-inch device to the iPhone upgrade cycle, Apple timed the iPhone SE product launch in March 2016 to happen alongside the public release of iOS 9.3.
The iPhone 7 is expected to launch in September 2016 with iOS 10.0 (which could be named iOS X).