On the Liberty Street Economics blog,
First, institutional prime and muni funds—but not retail or government funds—must now compute their net asset values (NAVs) using market-based factors, thereby abandoning the fixed NAV that had been a hallmark of the MMF industry. Second, all prime and muni funds must adopt a system of gates and fees on redemptions, which can be imposed under certain stress scenarios.
Investors adjusted their portfolios in response to these changes:
… investors’ shift from prime and muni funds to government—and, in particular, agency—funds means that a large segment of the industry still operates under a stable NAV (and therefore is, in principle, vulnerable to runs). … Since the new regulations have resulted in a very large shift of assets into relatively safe government funds, the SEC’s reforms have made runs on MMFs less likely and the industry itself more resilient.