How Hayekian is Sunstein's behavioral economics?

I comment on Sunstein's paper proposing ‘Hayekian behavioural economics’. In essence, Sunstein is merely renaming a familiar approach to normative economics, initiated in Sunstein and Thaler's seminal 2003 paper. I argue that this approach cannot fairly be described as in the spirit of Hayek's work. Sunstein's approach is based on a ‘constructivist’ conception of rationality that Hayek consistently criticized. Although both Hayek and Sunstein address ‘knowledge problems’, the two problems are fundamentally different. I develop what I claim are truly Hayekian critiques of Sunstein's claim that fuel economy mandates can be more Hayekian than carbon taxes.