Fidelity Investments announced Tuesday it is making the fee reductions on five of its index funds to 10 basis points, introduced last August, permanent. The reduction was the most dramatic on the Spartan International Index Fund, which had cost 47 basis points. But even as Fidelity touted the fee reductions as "A Perfect 10!" in advertisements, they included fine print saying, "This arrangement may be discontinued at any time."

The decision to make the reduction permanent comes on the heels of a barb by Jack Brennan, Vanguard chairman, that Fidelity had introduced the reductions as a mere " opportunistic marketing ploy" to compete with Vanguard's famously low-cost index funds and the growing popularity of even cheaper exchange-traded funds.

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