Originally Posted by Chris_W

Token are now also offering 11-speed cassettes that fit on 10-speed bodies. They're currently only offering 11-23, 11-25, and 11-28 cassettes and in a high-tech carbon spider with milled one-piece steel cassette, and so they're really expensive (in the range of US$300), but hopefully a wider range of sizes and options at lower price points will be available in the future. Here's the official product page and a report at BikeRadar.