Sneak. As in sneaking around, it is a subterfuge, a ploy, something hidden, not to be seen or noticed by everyone. Peek. As in take a peek, peek though the lens, peek a boo. Peek, as in looking at something briefly. Peak is the highest point of a mountain, the apex, the tallest part. Take a peek at Everest. Can you see the peak?
It is "sneak peek" and not "sneak peak."
Thank you, I don't care to tippy-toe my way to the top. I'd much rather get a glimpse that isn't for everyone.