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.