If you only need the last 90 days of OKX options candles, the public REST API will do. If you need years of tick-level trades, Greeks, or order-book snapshots across BTC, ETH, and alt options, you'll hit rate limits, missing candles, and painful pagination within an hour. I spent two weeks benchmarking three data sources on the same BTC-USD-250328-100000-C instrument, and this guide walks through the exact pipeline I shipped — including the rate-limit math, the async concurrency pattern, and how I used