According to https://www.irs.gov/individuals/international-taxpayers/figuring-the-foreign-earned-income-exclusion, dated 2 October 2017, the 2015 cap for Foreign Earned Income Exclusion was $100,800. How can I find out the 2017 and 2018 caps?
Answer: For taxable years beginning in 2017 or 2018, the caps are $102,100 and $104,100 respectively. Source was https://www.irs.gov/pub/irs-drop/rp-17-58.pdf, Section 3.34.
The FEIE is one of many IRS figures that changes annually based on a complicated inflation calculation. The IRS publishes a list of the changed values near the end of each year. In October when they published this, the tax code changes were still in progress, and the IRS pub states "To the extent amendments to the Code are enacted for 2018 after October 19, 2017, taxpayers should consult additional guidance to determine whether these adjustments remain applicable for 2018." I imagine that nobody updated the main link that turns up in most google searches, thus my difficulty finding the answer to the question.
Thanks to @kweinert.