Bittrex will support BTG (Bitcoin Gold).  Bittrex says “If you have a Bitcoin (BTC) balance on Bittrex during the BTG snapshot block 491,407 occurring approximately on October 24, 3am PT (10am UTC), you will be additionally credited the equivalent amount of Bitcoin Gold (BTG) on a 1:1 basis. i.e. 1 BTC on Bittrex held during the on-exchange snapshot will get you 1 BTG. BTC held on orders will also be credited. Only the BTC held on your account is eligible for BTG.”

“Bitcoin Gold codebase also contains a private premine of 8,000 blocks (100,000 BTG). Please be aware that if a market does open there is a possibility of the developers selling their premined BTG on the open market.

When considering adding tokens to Bittrex exchange we look at the risks involved. Bitcoin Gold does not satisfy our criteria for safety for our users. Taking a snapshot of the Bittrex exchange Bitcoin wallet is also a large disruptive undertaking that requires over 24 hours of preparation (Bitcoin deposits and withdrawals are also suspended during this time) and should not be taken lightly.

Bittrex will close deposits and withdrawals of Bitcoin (including 2nd layer protocol XCP/OMNI and associated assets) 24 hours prior to the BTG snapshot block 491,407 occurring approximately on October 24, 3am PT (10am UTC). The wallet will remain closed until the on-exchange snapshot is complete. Trading will remain active during this time.

Bittrex will make all reasonable attempts to credit our users BTG but until we have a fully supported wallet, we can neither guarantee tokens or consider creating a market. We will continue to monitor the state of the codebase and network. We’d also like to encourage the BTG development team to reach out to us.”

From https://support.bittrex.com/hc/en-us/articles/115002320451-Statement-on-Bitcoin-Gold-BTG-