from Department of the Treasury Resource Center:
"Effective Tuesday, October 16, 2018, with the inaugural auction of the new benchmark 8-week Treasury bill, Treasury plans to include 8-week bill rates in its input data set for the daily Treasury yield curve. Treasury also plans to add a 2-month CMT to the Daily Treasury Yield Curve Rates and 8-week bill rates to the Daily Treasury Bill Rates that it publishes."
https://www.treasury.gov/resource-center/data-chart-center/interest-rates/Pages/TextView.aspx?data=yield