35 Seats are up this time. No special elections are scheduled with them (yet).
Six have chosen to retire, and all but one are Republicans: Shelby (AL), Blunt (MO), Burr (NC), Portman (OH), Toomey (PA), and Leahy (VT)
Senator Inhofe (R - Oklahoma Class 3) is also resigning, spawning a special election there.
FINAL RATINGS
High Confidence
Highly Competitive
Full Ratings