Thanks for the question!
So the SNS will consist of multiple canisters. A first version of most of them (the governance canister, the root canister, and the ledger canister) already exist and are open sourced here.
We will further improve those canisters and also plan to add an initial token swap canister (as described in this forum post .
The SNS release where SNSs are deployed on a special subnet (see here) is targeted for the Carbon milestone.