3 years only if they are going to cut Mahomes (haha no). Its similar to how the Cowboys could have cut Tyron for very little this year.
Meanwhile CBS, Schefter, Rap, PFR (and I can keep going) are ALL saying the EXTENSION is 10 years (note 10 years not 12) worth 477 million with incentives that can push it to 503. Now those incentives are very unlikely to trigger (I think Schefter said there were 2 each year: 1 for winning AFC Championship and 1 for SB), but they exist and the 477 in guarantees is separate from that.