I got my 2010 GSX-SE with the 4 stroke engine in mid October. I will not be driving it until after December 22nd (end of deer season) or even later if we do not have any snow. The dealer filled the gas tank about 2/3 full. Should I put some stabilizer in the gas? Will it do any harm to run a brand new engine on gas with the stabilizer in it?

no reason to add stabillizer .

If you are worried I would just add some Seafoam.

No, just keep the battery charged.

X2 on some seafoam, never hurts.

Gas deteriorates in as little as 60 days. The warmer the temperatures, the quicker it deteriorates.
Given the sled is sitting for 2 months, that would be enough reason to add stabilizer. Stabilizer is cheap and won't damage a new or used engine.

Just have to top it up with new gas . If you think he should had stabilizer thats your opinion

rotax800, I have never had a problem with 4-stroke sleds and old gas. At the end of the season, my tank is normally about half full. When the season starts, I top-off the tank with fresh gas and go. You're talking about gas sitting for 60 days. Given my prior experience, I don't see any need to add any kind of gas treatment.

Just because - X's 3 on the Seafoam - I use it no matter what, when or how long its good stuff and does no harm and its also inexpensive.

Put it in, cheap insurance IMO especially with todays gas. Ya got a clean fuel system, keep it that way.