Judging by the looks of it, it's a feature that will allow you to trade without fees (after you've collected enough amount of credits).
Not really a bad deal if you trade a lot. Kinda looks like a loyalty program to me. Is it going to be 1 credit = 1 cents for every trade? This means If you trade $1000 and get $1000 worth of credits, your next trade is free but Bittrex won't get any commissions. Isn't it going to make them lose at least half of their revenue (assuming the number of users that use this exchange won't increase)?
Is there any clarity as to what happens with the credits and how the system works?
I decided to trade a few ADA for BTC at Bittrex to check this feature out; I traded 4080 ADA for BTC at the rate of 465 satoshis/ADA, and this is how it all went:


It all went smoothly. I traded without any trading fee (due to adjustment of these credits).
At the rate of $8100 per BTC, 0.00004743 BTC equals 38 cents. So it seems like 1 credit = 1 cent.