United Kingdom, up to 2 years of Tax Treaty

2 years of teaching/research tax treaty with unlimited exemption

Tax treaty for Professors, Teachers, and Researchers

A professor or teacher who is a resident of the United Kingdom on the date of arrival in the United States and who is in the United States for not longer than 2 years primarily to teach or engage in research at a university, college, or other recognized educational institution is exempt from U.S. income tax on income for the teaching or research. If the individual’s 2-year period is exceeded, the exemption is lost for the entire visit, including the 2-year period.

The exemption does not apply to income from research carried on mainly for the private benefit of any person rather than in the public interest.

(Reported from Internal Revenue Service (IRS), US government Publication 901)