Late May through October is the only practical season — the Khunjerab Pass is officially open 1 May to 30 November, but in practice it can close earlier or later depending on snow. June to September is best for travellers, with reliable conditions on both sides of the border.
Even in midsummer, nights at Sost can drop close to freezing. Winter is severe: temperatures below –20°C, daily snowfall, and the highway often impassable from Sost north. The local Wakhi population mostly winters further down the valley in warmer places like Gulmit and Karimabad.