They break down perfectly, with four currently Republican-held Senate seats and four Democrat-held seats on the ballot.
Note that, because he was running for the unexpired portion of the seat formerly held by the appointed Republican Kelly Loeffler, the seat of newly elected Democrat Raphael Warnock, D-Georgia, will be on the ballot, and he won that seat by just 51-49 percent in a state that had generally been dominated by Republicans in recent years. So Republicans will certainly be gunning for that one.
Note also that two of the currently Republican-held seats that IE rates as “battleground” races will not have incumbents, as North Carolina Republican Sen. Richard Burr and Pennsylvania Republican Pat Toomey have announced that they will not seek reelection. As of now, the incumbents are assumed to be running in all in the other races on the list.
I’ll emphasize again what I said in passing above. Inside Elections is not so much rating these races as toss-ups as they are noting that, with what little is known at the moment, and considering that they all occur in states that been closely divided in the past year or two, those races will likely be in play and that somewhere on this list are likely to be seats that might determine which party will control the Senate during the second half of Joe Biden’s just-begun four-year term.
The Inside Elections preliminary Senate race ratings page is here.