4k to 1080 = does FCPX automatically converts?

Hi there!
Just created a project with 1920 x 1080 / 29.97fps settings.
Then I imported a 3840 x 2160 / 29.97 footage.
And then voi-la: had to do nothing? FCPX simply adapts it to my timeline.
Premiere, per example (it's where I come from) doesn't do this.

That's pretty cool. But I'm wondering....do I have to convert this file (from 4k to 1080) or this FCPX adaptation is enough for the project?

Thanks!

That's the beauty of FCP. You need not waste time doing pointless stuff other NLEs demand you do.

It adapts automatically because by default FCP has Spatial Conform set to fit. This makes the footage fit the viewer for the project size, in your case scaling down the 4K footage to fit the 1080 HD frame. Spatial conform is located in the video inspector. You can click on your clip in the timeline and then select either fit, fill or none in the spatial conform setting to alter how the footage fits the frame. If you set to none, the 4K footage will be zoomed to its original size within the 1080 frame, allowing you to move the clip around the frame for closeup shots and reframing since only a portion of the clip would be visible. Maybe this helps to understand what is happening.