inertiajs.com/events (Vue3)

I would like to use the follow code found on https://inertiajs.com/events

import { router } from '@inertiajs/vue3'

router.on('before', (event) => {
  if (!confirm('Are you sure you want to navigate away?')) {
    event.preventDefault()
  }
})

I have not upgraded to the latest version of inertia. In my .vue files I have

//my .vue files
import { router } from '@inertiajs/inertia-vue3

which is different from the docs

//docs
import { router } from '@inertiajs/vue3'

//The error is
Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'on')

Does this mean I have to upgrade Inertia? That sounds difficult and scary. I would like to complete the project and then consider upgrading.

Obviously being the cunning man that I am I tried router.value.on() which made me feel retarded but I just wanted to note that I did try it.