Don't call Goldman Sachs Group Inc.'s long-awaited bitcoin-trading business a full-fledged desk, and don't expect it to buy and sell bitcoins, at least at first.

The bank, preparing to pioneer a new cryptocurrency market on Wall Street, plans to start small and offer a limited number of derivatives, according to a person briefed on the decisions. It will trade bitcoin futures in a principal, market-making capacity and will also create non-deliverable forward products.

Wall Street firms began offering clients futures from Cboe Global Markets Inc. and CME Group Inc. in December. But one issue with buying and selling actual bitcoins is that they can be stolen by hackers. That means any bank looking to facilitate those transactions will have to figure out how to guard such assets, a step that could require a nod from regulators.