You can extend it forever in 1-year increments. O-1 is dual intent. So while you're in the country you can apply for a green card through EB-2/3 (PERM or NIW)

You can extend it forever in 1-year increments. O-1 is dual intent. So while you're in the country you can apply for a green card through EB-2/3 (PERM or NIW) or EB-1.