Oxford & Merriam-Webster list both plurals and the author calls out that octopi is "the quite beautiful plural form of 'octopus' " which could be interpreted as "while there are multiple correct plurals of octopus, octopi is the beautiful one."

  While “octopi” has become popular in modern usage, it’s wrong.

I would argue that it used to be wrong, but language, unlike physics and code, is what the majority say it is.

I used to be a stickler for correct vocabulary usage and then I saw a documentary about dictionaries (can't remember what it was) and someone from OED said basically this (from https://www.oed.com/public/oed3guide/guide-to-the-third-edit...):

  The Oxford English Dictionary is not an arbiter of proper usage, despite its widespread reputation to the contrary. The Dictionary is intended to be descriptive, not prescriptive. In other words, its content should be viewed as an objective reflection of English language usage, not a subjective collection of usage ‘dos’ and ‘don'ts’. However, it does include information on which usages are, or have been, popularly regarded as ‘incorrect’. The Dictionary aims to cover the full spectrum of English language usage, from formal to slang, as it has evolved over time.

Now I think it's something that is just fun to argue about, but I don't take any of it seriously.

(edited for formatting)