UPDATE: In episode 5, host Ryan Devlin indicates that at least one non-truth-booth match is necessary to avoid a blackout. That increases the chances of a blackout - my guess is that the odds approximately double.
1,334,961 out of the 3,628,880 (36.8%) possible combinations have zero perfect matches. We won't know exactly which 1,334,961 are the zero perfect matches until later in the season, of course.
The probability of a blackout in the first episode is 36.4%
Note that it's not possible to calculate the odds of a blackout during any subsequent matchup ceremony prior to a perfect match. This is because the contestants don't know which combinations are correct before they go into the matchup ceremony, so oftentimes they will pick a combination that already has been eliminated. The contestants are usually trustworthy enough to not pair up in possibilities that have already been eliminated in truth booths or blackouts, but they don't have the time or tools to ensure that their guess hasn't already been invalidated through other rules.
Overall, though - we know that the chances of a blackout in any given season is more than the 36.4%
I do have information at the time of the matchup ceremony what the chances of that combination being a blackout are, and I'll post that with each episode going forward.