If you own an iPhone X or older - you should throw it over the next bridge

Which iPhone models will get iOS 18
https://www.zdnet.com/article/every-iphone-model-that-can-be-updated-to-apples-new-ios-18-public-beta-and-which-ones-cant/

In keeping with Apple having the worst hotfix support in the industry,
Apple is the only operating system vendor who fully supports only a single
release (all other OS vendors except Apple have always fully supported
multiple releases simultaneously - so it's just Apple whose support sucks).
 <https://screenrant.com/apple-product-security-update-lifespan/>
 <https://support.apple.com/guide/deployment/about-software-updates-depc4c80847a/>
 <https://hothardware.com/news/apple-admits-only-fully-patches-security-flaws-in-latest-os-releases>
 <https://arstechnica.com/gadgets/2022/10/apple-clarifies-security-update-policy-only-the-latest-oses-are-fully-patched/>

According to Apple, these iPhone models will get iOS 18 when it becomes
widely available:

iPhone 15
iPhone 15 Plus
iPhone 15 Pro
iPhone 15 Pro Max
iPhone 14
iPhone 14 Plus
iPhone 14 Pro
iPhone 14 Pro Max
iPhone 13
iPhone 13 mini
iPhone 13 Pro
iPhone 13 Pro Max
iPhone 12
iPhone 12 mini
iPhone 12 Pro
iPhone 12 Pro Max
iPhone 11
iPhone 11 Pro
iPhone 11 Pro Max
iPhone XS
iPhone XS Max
iPhone XR
iPhone SE (2nd generation or later)

Notably, the once-popular iPhone X model is not on the list.

In addition, all older devices like the iPhone 8 series also didn't make
the cut this year. As for what's to come, Apple is expected to announce the
iPhone 16 lineup in September with iOS 18, presumably with new A18 silicon.