Currently fermenting - Carboy too big?

I just started my first simple cider. Just juice and notty yeast in there.

Its been fermenting about 48 hours, and already seems to be calming down. Still bubbling quite a bit, but the foam is dying down.

I used a 6.5 gallon carboy for 5 gallons of juice, for room if it bubbled up, but that didn't happen, so there's lots of room at the top.

I was planning to keep things in the primary for 3 weeks. Is this risky with all that space? Should I grab a 5 gallon carboy and rack to it after a week or so?

Thanks everyone

TMANIAC

It's good, the CO2 produced from your fermentation locks out all oxygen. You don't really need a secondary if you let it sit 3-4 weeks in your primary... on the yeast. Just bottle or keg straight from your primary after that time, assuming your FG reading is stable.

Thanks Djinn! Exactly what I wanted to hear.

TMANIAC