How long do you have to live abroad to be considered an expat?

Generally, to meet the physical presence test, you must be physically present in a foreign country or countries for at least 330 full days during a 12-month period including some part of the year at issue.

https://www.irs.gov/individuals/international-taxpayers/foreign-earned-income-exclusion-physical-presence-test#:~:text=Generally%2C%20to%20meet%20the%20physical,of%20the%20year%20at%20issue.