The traditional “big three”—Vanguard, Fidelity and T. Rowe Price—still dominate the rankings; they’re the only providers whose market share in TDFs is in the double digits: 34 percent, 18 percent and 15 percent, respectively.

And although Fidelity has retained a second-place ranking, its target-date assets have fallen by 3 percent from 2014 to 2015. Its first- and third-place competitors, however, have grown their share of target-date assets, with Vanguard racking up a 15 percent increase and T. Rowe Price adding 11 percent.

The fourth- and fifth-place finishers, BlackRock and J.P. Morgan, have also increased target-date assets under their management.

Then there’s the question of open architecture vs. closed architecture. With open architecture, a provider can use its own and others’ funds and fund managers for TDF investments. But, according to the study, different providers interpret open architecture differently.

Of the 26 respondents participating in Cerulli’s 2016 target-date provider survey, 54 percent described their target-date product(s) as closed architecture; 31 percent said they were open, and 15 percent said they offered both open- and closed-architecture target-date products.

However, 75 percent of the providers that said their product was open architecture said that at least half the total assets in the target-date strategy are allocated to the investment strategies of affiliated asset managers. So, Cerulli said, that product could be 51 percent allocated to nonaffiliated managers and 49 percent to proprietary strategies—but that’s not necessarily as “open” as the “open architecture” label would have people believe.

The second-largest group of respondents—17 percent—said their open-architecture target-date product only allocates up to 24.9 percent to nonaffiliated asset managers.

The Department of Labor has a few words to say, too, about open- versus closed-architecture funds. In its 2013 release, “Target Date Retirement Funds—Tips for ERISA Plan Fiduciaries,” it specifically urged plan fiduciaries to reconsider their choices on TDFs, listing “Inquire about whether a custom or nonproprietary target-date fund would be a better fit for your plan” as a recommended practice when choosing a TDF.

DOL also pointed out that “nonproprietary TDFs could also offer advantages by including component funds that are managed by fund managers other than the TDF provider itself, thus diversifying participants’ exposure to one investment provider.” DOL may not use the term “open architecture,” but in describing the potential benefits of a nonproprietary TDF it conforms to the industry’s understanding of an open-architecture approach.