Robo-adviser Betterment is growing its enterprise business with a new product for health insurers and their customers.

The New York-based company is partnering with United Healthcare and Optum Bank to launch a “simple, smart, automated” health savings account (HSA) for United Healthcare customers, CEO Jon Stein announced at CB Insights’ Future of Fintech conference in New York Wednesday.

“It will be the low-cost, smart HSA solution and hopefully will bring HSAs to many more people,” Stein said. “We will share that HSA account with your IRAs and your 401(k)s and will manage across all of those accounts to coordinate taxes.”

At $50 billion invested in HSAs nationally, account adoption is growing quickly (20 percent per year), Stein noted, adding that United Healthcare has 4 million HSA account holders. It’ a space that’s reminiscent of the “early days of the 401(k)” and which Betterment has been eyeing for years, he said.

Betterment, like other digital investment platforms including Wealthfront, Stash and Wealthsimple, has steadily grown its product and feature set in recent years to differentiate its offering. That includes Two-Way Sweep, a tool that moves money from customers’ bank accounts into a Betterment account that’s designed to provide a higher return, as well as messaging with human advisers for digital-only customers and a charitable giving feature.

The HSA product adds to the company’s B2B product suite, which includes Betterment for Advisors, a technology platform for financial advisers, and business 401 (k)s. “Our big B2B play is the 401(k). It’s the way that we reach the most customers [and] that’s a primary focus for me,” Stein said. “We’re working with more than 500 employers — companies like Casper, Fox, Bird and Compass — who are looking to provide a leading company benefit to savvy employees who demand the best.”

Betterment currently has more than $16 billion in assets under management.