Tax-exempt bonds are yielding more than Treasuries for the first time since the financial crisis, a relationship that history shows doesn’t last, especially as the Federal Reserve kindles inflation expectations.

Investors buying AAA municipal general obligation bonds due in two years get a yield equal to 119 percent of similar- maturity Treasuries, Bloomberg Fair Market Value data show. A ratio above 100 percent means those in the 38.3 percent federal tax bracket get higher yields plus tax-sheltered income. Before the credit crisis in 2008, that happened twice in the 20 years for shorter-maturity debt.