I also got this message from Bittrex that my account is now enabled to earn Bittrex credits when I trade. Is this for all Bittrex users?
I'm not active in trading there these past few months, no email recieved, but I got the same pop up after logging in. I think all KYC verified Bittrex International users' received that, regardless if you're active or not. I recommend that you read the Medium post (link given by @Raja_MBZ), they have mention dates there about expiration.
Is this bittrex credit is also a token like bnb in binance ? or just normal credit that you can use only to decrease widrawal transactions or exchange fees . If its like binance token and they give it for free to traders well i want to buy now maybe this token might be the same as bnb that increase its value .
No it's not like BNB. Bittrex credits has no monetary value, you can only use it to have a commission-free trade (it depends on the amount of credits you have though). Another thing is it's still in beta, if they will implement it in the future or not, we are not certain of it yet.
More info about the credits:
https://bittrex.zendesk.com/hc/en-us/articles/360032289972-Terms-of-Service-Addendum-for-Bittrex-Credits-Beta-Program