Their official statement mentions how GDAX “only supports trading and withdrawal for ETH”. There is absolutely no mention of ever supporting ETC, but the bigger question is what they will do with the corresponding Classic tokens. For now, all of the ETC associated with the Ethereum hard fork balances is being kept in cold storage. Or to put it differently, GDAX owns all of the users’ ETC and will keep them locked down until mentioned otherwise.
http://fintechist.com/gdax-plans-keep-users-post-hard-fork-etc-funds/
