The market of private health-insurance exchanges for active employees is quite immature. But a brief consolidation phase may have already been completed with today’s announcement that Towers Watson has acquired Liazon for $215 million.

Towers Watson is among several human-capital consulting firms, including Aon Hewitt, Mercer and Bulk Consultants, to have launched private exchanges for active employees in the past 18 months. Six-year-old Liazon is the largest player in the market by one measure: its number of corporate customers. There are 2,400 of them, although the vast majority have fewer than 50 employees. Liazon’s exchange platform is distributed via insurance brokers under either the Bright Choices brand name or as a third-party proprietary exchange.

Towers Watson will continue to offer its own OneExchange platform, which has sought to serve employers with many thousands of employees, and to use the Liazon name in its interactions with brokers.

The other major stand-alone private-exchange vendor, Bloom Health, was jointly purchased by Health Care Service Corp., Wellpoint and Blue Cross Blue Shield of Michigan in 2011.

One observer speculates that Towers Watson needed Liazon because developing its active-employee (as opposed to retiree) business has been slow going. “One could argue that Towers hasn’t been as successful as some of its competitors in that market,” says Chris Condeluci, a health-care attorney with law firm Venable LLP, who has developed a specialty in private-exchange matters.

Indeed, Towers Watson so far has only three corporate clients, averaging 15,000 covered lives each, for OneExchange. Meanwhile, Aon Hewitt recently announced it had lined up 18 corporations with more than 3,000 employees each as customers of its active-employee exchange in 2014, and Mercer said 33 corporate clients with head counts of between 100 and 30,000 will use its platform next year. Buck has said it will be serving five companies with more than 3,000 employees.

Towers Watson has plenty of good reasons for buying Liazon, says Bryce Williams, the firm’s managing director of exchange solutions. “The market is moving so rapidly, and there’s a sense that a tipping point is being achieved,” he says. “There aren’t many companies that have been in the active-employee private exchange market for more than a year or two. Liazon has been at it for six years, and there aren’t really any others left with Liazon’s technology capabilities that aren’t owned by someone else. It’s as if the music just stopped and we grabbed the last chair.” Condeluci, for his part, calls Liazon’s technology platform “one of the best in the business.”

Towers Watson got into the exchange business by purchasing Extend Health, a Medicare platform for retirees, in May 2012. Some of Towers’ consulting-firm competitors developed their exchange technology in-house.

The potential market is certainly broad. There are about 150 million Americans covered by employer-sponsored health insurance, and the market is clearly poised to move in any number of directions. By some estimates, tens of millions of employees could move to private exchanges over the next few years.

Williams notes that while Liazon’s customer base is still composed mostly of small employers because that was its initial focus, the company is “now selling to clients with a couple thousand covered lives. It’s going up-market.”

The larger Liazon accounts won’t be moved to OneExchange. “We really like the scalability of Liazon’s platform up to 5,000 or maybe 10,000 lives,” Williams says. “We’re thinking of that as a break point under which the Liazon platform would work beautifully. For us, this is a market complement and a speed-to-market strategy for midsize and small groups. As a global benefits consultant to the Fortune 1,000, Towers Watson has not played in that space.”

Liazon co-founder and CEO Ashok Subramanian will continue to run Liazon, reporting to Williams. Plans are to continue operating it as before. Towers Watson took that approach as well with Extend Health, the retiree exchange business, which is seeing strong growth. “When you acquire a company that has intense entrepreneurial speed and spirit, keep that alive and keep that culture going,” Williams says.

Williams also likes that Liazon has distribution deals with nine of the 10 largest mid-market health insurance brokers and that its platform is set up to serve both fully insured and self-insured employers. “That was highly attractive to us, because our first platform was built exclusively for self-insured,” he says.