iOS popup close button label: "OK" or "Okay"?

Question

I'm working on an iPhone app with custom popup alerts. In the design these alerts all have "Cancel" buttons, but since there is nothing to cancel in these cases, I want to change them to "Okay" buttons.

My question is this: What are the Apple guidelines regarding these button labels? Should it be "Okay" (which is my personal preference), or should it be "OK" (which I don't like because it looks like teen-text-speak or the state abbreviation for Oklahoma).

Answer 1

OK is what Apple uses for settings and their iPhone apps.

Answer 2

Apple's Human Interface Guidelines say to use "OK", so its best to stick with that for consistency:

Use OK for simple acceptance. Avoid using Yes or No.

They have a few additional helpful tips on the subject:

Give alert buttons succinct, logical titles. The best button titles consist of one or two words that describe the result of selecting the button. As with all button titles, use title-style capitalization and no ending punctuation. To the extent possible, use verbs and verb phrases that relate directly to the alert title and message—for example, View All, Reply, or Ignore.