Apparently the majority of English speakers say octopuses (which is my preference as well, but I'm not a native speaker).

By the way, how do you pronounce octopi? Is it "octo-pee" or "octo-pie"?

You're missing a word, but it seems like you're saying octopuses is wrong. But it's right, and not just because a spot informal weird had been accepted: it's technically correct. As sibling comments have said, the original plural would be octopodes because it's from the Greek, not octopi because it's not from Latin, but English doesn't normal take Greek plurals.

I’ve long wanted it to be octopi but my iPhone and most sources say no. Out of the dictionaries, only Oxford English seems to include but says based on a misunderstanding. Some detail on history here:

https://en.m.wikipedia.org/wiki/Octopus under pluralisation

Interestingly:

> Historically, the first plural to commonly appear in English language sources, in the early 19th century, is the latinate form "octopi"

That’s quite late and interesting the “wrong” one was first.

Now that you mention it, I'm not sure if I've heard platypi or platypuses more.

Tasmanian here.

It’s only platypuses if you see more than one at a time, and that’s pretty much never gonna happen ;)