Depends what you need it for. For a quick read, the OSRS Wiki real-time prices API (prices.runescape.wiki) is free, public, and updates every few minutes — that's what most price-check tools actually pull from. The official GE API exists but it's cached daily, so it's near-useless for live prices. If you mean gold (RWT) market rates rather than in-game GE prices, there's no single feed — you have to aggregate seller listings across sites yourself. What are you trying to build or track?