Photons do not have an upper limit on energy, even beyond gamma rays. The Planck energy is significant but not a definitive limit, as current quantum field theory (QFT) does not impose a maximum energy for photons. However, issues arise at the Planck energy due to the influence of gravity, which is not accounted for in QFT. Additionally, QFT is considered a low-energy effective theory, suggesting that its predictions may break down at high energies. Thus, while theoretically unlimited, practical constraints exist at extreme energy levels.