It requires bluetooth 4.0 low energy which the gs4 has. Apparently the stack that Samsung uses in touchwiz works. I don't see why googles wouldn't.
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Phone: [AT&T Galaxy S4 SGH-i337] Rom: Task650 AOKP
Tablet: [Galaxy Tab 8.9 LTE SGH-i957] Rom: ICS 4.0.4 UCLK4
Dog: [Pitbull Sharpei Mix] Rom: Stock