Google's Project Fi is going unlimited.

In a Wednesday blog post, Project Fi Product Manager Marcia Jung announced a new feature called Bill Protection, which "combines the simplicity of our existing pricing with the flexibility of an unlimited plan." The feature is rolling out today to individual subscribers and group plans.

Here's the deal: Project Fi normally costs $20 for the first line, $15 for each additional phone line, $10 for each additional tablet, and $10 per 1GB of data. With Bill Protection, you won't pay more than $80 a month for call, text, and data charges on a single line, regardless of how much data you use.

"In months when you use more than 6GB of data, we'll cap your charges for calls and texts plus data at $80, and allow you to continue using high speed data for free—similar to an unlimited plan," Jung explained. So, if you wind up using 9GB of data in a month, for instance, you'll only have to pay for 6GB.

If you have two lines on your plan, Bill Protection kicks in after you collectively use 10GB, capping your bill at $120 a month (excluding taxes and fees). With three lines, it kicks in after 12GB ($135), with four lines at 14GB ($150), with five lines at 16GB ($165), and with six lines at 18GB ($180).

The biggest data hogs will be throttled.

"If you're a super heavy data user, you'll experience slower data speeds in months when you've consumed more than 15GB of data," Jung wrote, adding that this should affect less than 1 percent of users). If you can deal with that caveat, you can "opt out of slower speeds by paying $10/GB for your individual data usage above 15 GB."

Rest assured that you will only pay for unlimited data when you reach the Bill Protection threshold. So, "if you only use 1.4GB of data, at the end of the month you'll pay just $34 instead of $80."

As we wrote in our review, Project Fi "combines Sprint, T-Mobile, and U.S. Cellular into a virtual network with better coverage than any one of the three offers individually." The main downside is the selection of phones you can use with this service is very limited. Still, "its spectacular results in our annual Readers' Choice poll mean it's worth considering if you're interested in Google's Pixel phones," we wrote.