This article presents a new method for embedding optical fibers into a nickel alloy and gives the results for a long-term test with thermal cycling of two fiber-optic Bragg gratings embedded in nickel alloy. We embedded these Bragg gratings in a piece of Inconel 600 (a nickel alloy) using vacuum brazing. We then thermally cycled this piece between 500, 525, and 550°C for about six months while monitoring the reflected wavelengths of the gratings. We tested two other embedded gratings for 68 hours at 600°C. Some microscopic cross sections of the embedded fibers are presented. The results show that fiber sensors embedded in metal can operate reliably at very high temperature and in harsh environments. We hope that the results from the long-term, elevated temperature test will make it possible to apply the technology of fiber-optic sensing in new and demanding monitoring applications, especially at high temperatures in energy production.