Topological insulators (TIs) possess an insulating bulk and spin-momentum-locked Dirac-like surface states which are topologically protected from backscattering. This connection between charge and spin currents makes TIs highly attractive for spintronics and quantum computing applications where spin-encoded information needs to be coherently transmitted and processed with high-fidelity. However, the physical limits of quantum coherence in TIs have not yet been fundamentally understood. Here we demonstrate by scanning tunneling spectroscopy (STS) measurements at high magnetic fields that the broadening of Landau level (LL) states in Sb2Te3 exhibit a maximum width at the zeroth LL and monotonously decrease away from the Dirac energy. The weak magnetic field dependence verifies that the spin–orbit-induced spin texture of topological states effectively protects them from scattering even at the highest achievable magnetic fields.