http://www.faa.gov/other_visit/aviat.../info08012.pdf
It's Level 4, "officially". It will expire, "officially", three years after the date of issue on your license. No one in FAA intended that this be so, but at least one country wants their FAA-licensed expats to take an English proficiency exam based on this interpretation. To my knowledge no CAA is hassling US airline pilots flying international over this,
yet. I expect FAA will do some sort of a change soon, but what it will be I have no idea. The workaround is to order a replacement license every three years - it'll have a new issue date.