A look at new enrollments in 401(k) retirement plans shows that hiring cooled to 1.3% in August, its slowest pace since June 2020, according to Vanguard data. That's below the government's 3% Job Openings and Labor Turnover Survey (JOLTS) data for July.

Traders are waiting on the second-quarter GDP revision and weekly jobless claims data to roll out on Thursday. Micron reports earnings after the closing bell.

Iran launches missiles at Israel, triggering a selloff in US stocks and jump in oil prices. Markets are unnerved but not yet panicked, analysts said.