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For decades, index funds have been the gold standard for retirement investing. Cheap, diversified, and easy to manage, they’ve helped millions of Americans adopt a simple buy-and-hold strategy built around broad-market indexes.

But the world’s largest asset manager is now warning that relying on index funds alone may no longer be enough.

“There needs to be an evolution away from this being indexed only,” Nick Nefouse, global head of retirement solutions at BlackRock, said in a phone interview with Bloomberg (1). “The markets are evolving to a point where there needs to…