The white paper says 1 SBD.

"SMT creation fee
Issuing a smt_create_operation requires payment of smt_creation_fee. The amount required is set by the smt_creation_fee field of dynamic_global_properties_object. This field may contain a value in STEEM or SBD. If specified in SBD, an equivalent amount of STEEM will be accepted, at the current price feed.
Initially, smt_creation_fee will be set to 1 SBD, and no means will be provided to update it. Updates to the smt_creation_fee amount may occur in future hard- forks, however, so user-agents should read the smt_creation_fee value from the dynamic_global_properties_object. User-agents should not assume the fee will always be 1 SBD and they should be prepared to charge a separate fee paid to the user-agent if the aim of the interface is to enable only a curated set of tokens.
The fee is destroyed by sending it to STEEM_NULL_ACCOUNT."