Can I use my own modem for the unlimited data plan?

Do you need xFi Complete for unlimited, or can you get unlimited on it's own?

... do I NEED to use their modem to take advantage of the unlimited data ...

You can, you just have to pay more for it than you would pay to rent Comcast gear.

https://www.xfinity.com/support/articles/exp-unlimited-data says:

... there are two ways you can get unlimited data from Xfinity. ...

Option 1: You can purchase the Unlimited Data Option. ...  [$30/mo]

Option 2: Customers who lease an xFi Gateway can add xFi Complete, which includes unlimited internet data. ...  [$20/mo]

Prices from https://www.xfinity.com/learn/internet-service/xfi-complete.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

@XfinityBrandon wrote: "... Unlimited ... $14.00 per month with an xFi Gateway. ..."

This is incorrect. Gateway rental alone is $14.00 (or $15?) per month, but if a customer wants Unlimited they have to sign up for xFi Complete, which is $20.00 (or $25?) per month. See https://www.xfinity.com/learn/internet-service/xfi-complete:

Add xFi Complete

Includes the xFi Gateway when you add xFi Complete to any eligible internet plan for an additional $20/mo.

@kevbodia  Hello there! Yes, you absolutely can use your own approved device. You can add the Unlimited Data Plan for $30.00 per month without xFi Complete, using your own gateway.