This work investigates the thermal stability of point defects in high-purity SiC. Electron paramagnetic resonance measurements made after Ar annealing between 600°C and 1700°C reveal changes in at least two defects, a carbon vacancy related center (VC) and the shallow boron acceptor. Between 1000°C and 1400°C, the number of carbon vacancies decreased and the number of boron acceptors increased in about the same proportion. Above 1400°C, the concentration of B continued to grow, while the number of carbon vacancies fell below the detection limit. After the highest temperature anneal, the initial preannealed concentration of VC was restored by illumination with sub-bandgap 578-nm light. The effects of heat treatment between 1000°C and 1400°C are interpreted in terms of the charge exchange between a compensated B acceptor and VC. The observation of optically induced carbon vacancies after the final anneal suggests that they are thermally stable in these samples up to 1700°C.