What is the plural of octopus?

The Oxford English Dictionary lists octopuses, octopi, and octopodes (the order reflecting decreasing frequency of use), stating that the last form is rare.

English words of Latin or Greek origin have rather unpredictable plurals, and each one usually depends on how well established that particular word is. It may also depend on whether the Latin or Greek form of the plural is either easily recognizable or pleasant to the speaker of English.

Although it is often supposed that octopi is the ‘correct’ plural of octopus, and it has been in use for longer than the usual Anglicized plural octopuses, it in fact originates as an error. Octopus is not a simple Latin word of the second declension, but a Latinized form of the Greek word oktopous, and its ‘correct’ plural would logically be octopodes.

Merriam-Webster: plural octopuses or octopi

Wikipedia: There are three plural forms of octopus: octopuses, octopi, and octopodes. Currently, octopuses is the most common form in the UK as well as the US; octopodes is rare, and octopi is often objected to as incorrect.