Starting today, Comcast is letting its customers use a Roku as a secondary cable box. If you’ve got a Roku streaming device “released in the last couple years” — or a Roku TV — you can download the Xfinity TV app beta from the Roku store and give the experience a test run before it widely launches later this year.

Eventually the plan is to let customers replace their cable box (but not a cable subscription, obviously) with a Roku if they so choose. But during the beta phase you’ll need at least one Comcast cable box in your home somewhere. Comcast says this is “due to technical limitations.”

Beta participants will get full live and on-demand programming, and the beta app can also play back your cloud DVR recordings. What it can’t do (yet) is rent / buy content or play back previously purchased content. SAP availability may also be “intermittent” during the pre-release period, according to Comcast’s FAQ page on the beta run.

You’ll need to be connected to your home Wi-Fi network to use the beta app; it won’t work if you take your Roku box elsewhere. And as is increasingly becoming the case with these type of services, Comcast isn’t counting it against user internet data caps:

The Xfinity TV service delivered through the Xfinity TV Beta app is not an Internet service and does not touch or use the Internet. Rather, it is a Title VI cable service delivered solely over Comcast's private, managed cable network, so it will not count toward your Xfinity Internet Data Usage Plan.

This Roku-as-cable-box idea is by no means new; Spectrum (formerly Time Warner Cable) has been offering something similar for a long time now. Comcast previously experimented with the same concept on Xbox 360. The Roku devices that are compatible with Comcast’s Xfinity TV beta are as follows, and keep in mind that TVs with Roku built in are also supported: