QHP buyers like silver

For a family on a silver plan with an income at 150 percent of the federal poverty level, the cost-sharing assistance reduces a $12,700 annual out-of-pocket maximum to $4,500, and for an individual, from $6,350 to $2,250, Mahoney said.

The cost-sharing subsidies were intended to encourage consumers to "buy up," Mahoney, senior vice president of consumer marketing at GoHealth, said in a telephone interview.

Health insurers are assuming that the patients signing up for gold plans and platinum plans will be older and sicker than average, said Brian Wright, a New York-based analyst at Monness Crespi Hardt & Co.

"So overall, the greater the percentage of enrollment in the bronze and silver plans, the better from a risk pool perspective," Wright said in a telephone interview.

Bruce Broussard, chief executive officer of Humana Inc. (NYSE:HUM), said early enrollment in higher metal tiers at his company was "greater than we anticipated," with 25 percent of customers picking a platinum plan, and 52 percent picking silver as of Dec. 31.

In January, the company has seen members start to skew younger and pick more silver plans, Broussard said in a call with analysts on Feb. 5.

Joseph Swedish, chief executive officer of WellPoint Inc. (NYSE:WLP), which has the most plans on the public exchanges, said silver and bronze plans were the "most popular metal levels by a wide margin." This was "consistent with expectations," he said in a call with analysts on Jan. 29. At the end of January, WellPoint had 500,000 new members enrolled through the exchanges.

–Editors: Andrew Pollack, Bruce Rule

See also:

• Prof gauges exchange death spiral risk
• Cap squeezes exchange plans
• DC exchange users prefer platinum