Plasmonic tungsten oxide nanocrystals (NCs), which dynamically modulate visible and near-infrared (NIR) light, are promising electrochromic materials for energy-efficient smart windows. Proton electrolytes can further enhance electrochromic responses by enabling rapid proton-coupled ion/electron transfer (PICET), owing to the exceptionally small size of H+.[1] However, most proton-based electrochromic systems rely on aqueous acidic electrolytes, which suffer from solvent evaporation [2], hydrogen evolution reactions (HER) [3], parasitic NIR absorption [4], and accelerated degradation of tungsten oxide NC electrodes. Here, we develop a non-aqueous proton electrolyte to overcome these limitations. Despite the use of a strong proton donor, proton transport is hindered by a solvent-dominated solvation environment, resulting in sluggish PICET kinetics. By introducing a multifunctional electrolyte additive, the local proton solvation environment is effectively reconstructed, facilitating proton desolvation and accelerating PICET. In addition, the additive stabilizes the nanocrystal/electrolyte interface, enabling stable electrochromic operation. These findings demonstrate that rational control of the proton solvation environment and electrode/electrolyte interface provides an effective strategy for achieving fast and durable electrochromic responses, highlighting electrolyte engineering as an important design parameter beyond conventional electrode-centered approaches.