Isn't the minimum length 3 years for a RFA? Pretty sure the only way he stays for one year is if he signs the QO.
Offer sheets for RFAs need to be at least two non-option years (unless they receive a maximum qualifying offer, in which case it’s longer, but that’s not happening here). However, the Celtics would not be signing him to an offer sheet, so even a 1-year deal greater than the qualifying offer is permissible.
It doesn’t make too much sense for the Celtics to do this, but it may be a good-faith gesture that earns them a right of first-refusal in the summer of 2019. It would also increase the amount of salary the Celtics could take back in a Smart sign-and-trade in 2019, through the base-year compensation mechanism. This would allow the Anthony Davis dream to live on.
I would consider this the least likeliest if possible outcomes, but it does have a rightful place on the possible outcome list, and we’ve seen Ainge offer a 1-year high-value deal to an RFA before (Jeff Green in December 2011 — although that deal was voided after the heart condition was discovered).