The front page of Arapahoe Basin’s website reads “we are open for the 2024-25 winter season for as long as possible” and they just determined what is possible. The answer is June 8th:
“We will ski & ride 7 days a week until June 1. After June 1, we will close for the week and reopen for the weekend of June 6, 7, and 8. Does this mean? Yes it does — As of right now, plan for June 8 as closing day for the 24/25 Winter Season! -Arapahoe Basin
If you plan on going to A-Basin keep in mind there is currently no remaining beginner terrain, only intermediate and above. Also heads up if you plan to ski on the extended weekends into June, the mountain be closing early at 2:00pm to help their snow refreeze to improve conditions for the following day.