Comment by fungizid

The steep increase at the end mostly does not reflect a change in economic fundamentals but rather banks relabeling savings accounts as transaction accounts in response to regulatory changes. If you look at M2 instead of M1, the increase disappears.

More info: https://fredblog.stlouisfed.org/2021/05/savings-are-now-more...

(Edit: Updated link to a more recent blog post)