I assume 5.4 is just the latest version. So if I'm on 5.1, I need to plan to upgrade to the latest version. I may assume the pricing is roughly the same, as well as the speed, and the purpose.

If I'm on Haiku, I don't assume I need to upgrade to Opus soon. I use Haiku for fast low reasoning, and Opus for slower more thoughtful answers.

And if I'm on Sonnet 4.5 and I see Sonnet 4.6 is coming out, I can reasonably assume it's more of a drop in upgrade, rather than a different beast.