"In 2021, our central bank let us down quite badly," hurting policy makers' credibility, Summers said on Bloomberg Television's "Wall Street Week." "It made mistakes in the core functioning of a central bank," including in its failure to lean in against fiscal stimulus last year, he said.

Among the errors has been a "repeated poor forecasting record -- and I have to say that it's not something that's been fully fixed," Summers said. The June median Fed official predictions showed inflation coming back toward the 2% target but unemployment only reaching a high of 4.1% by 2024 -- a "highly implausible" result, he said.

"Frankly I think in 2021 our central bank lost its way. It was talking about the environment, talking about social justice in a range of things," Summers, a Harvard University professor and paid contributor to Bloomberg TV, said. "It was confidently dismissing concerns about inflation as transitory."