According to BBC news: https://www.bbc.co.uk/news/uk-65435426
There are hopes that people will say out loud: "I swear that I will pay true allegiance to Your Majesty, and to your heirs and successors according to law. So help me God."
The Archbishop of Canterbury will then proclaim "God save the King", with all asked to respond: "God save King Charles. Long live King Charles. May the King live forever."
This is surely madness. Asking everyone in the Abbey - sure. People crowding nearby might be swayed to say "Hail the King" or something similarly short. But hoping for video footage of crowds in parks and pubs shouting a great long sentence that most don't fully buy into, then doing it again and with "live forever"! Does Charles really think he's liked that much? Is he? It doesn't seem very British at all, and seems destined to be a mess of people saying random stuff loudly.