Version 9.4, first announced in September, is now rolling out to “select 4K Roku devices", including the Roku Ultra player, Roku Streambar, Roku Smart Soundbar, Roku Streaming Stick+, and Roku Premiere.
Support for HomeKit means you can enable things like Siri control for your Roku device, while AirPlay 2 - perhaps the bigger offering - is Apple's proprietary casting protocol. It allows you to get your content off the iPhone, iPad, or Mac and stream it directly to a Roku device to view on a big-screen TV.
That's going to be great for sharing photos or videos or watching content that's not otherwise supported on the Roku platform.
Roku OS 9.4 also introduces a live TV channel guide, for a better look at everything that's now free to stream. And, if you have an antenna connected, you'll see over-the-air broadcast channels. The free software update also includes more controls for multi-channel speaker setups.
Be sure to check out our guide here on the best Roku devices to buy. We also have these handy explainers and buyer's guides on HomeKit and AirPlay 2: