Also keep in mind that I Bonds have a 3 month penalty if redeemed within 5 years.

but even so, I would go with the I Bonds. There is currently a 0.4% fixed rate. That means the inflation-based rate only needs to be 4.1 to stay even with the CD. I might be a pessimist but I don't see inflation coming down that fast. Also, with I Bonds you get interest on the entire month you invested it so you can theoretically buy a 4 week treasury now and then buy the IBonds and still get the full interest for December.