Rendering Question

When I render out a 3840x2160 rez clip on my timeline (which is set to 1920x1080), but my output resolution on the deliver page is 3840x2160, how will it handle the rendered clip? Will it upscale from 1920x1080 to 3840x2160? Or will it render the clip utilizing the source resolution of 3840x2160, and effectively just transcode it? I just want to know so I can avoid the upscaling, and if need be, switch my timeline resolution to 3840x2160 before rendering clips for VFX etc.

It will upscale. Output scaling is the last thing in the process tree.
You can change timeline resolution, but when you do some operations like node sizing don't scale. Sharpen/Soften, some FX might look not exactly the same. So it might take some manual tweaking to get it right.

Is it really worth it? Upscaling looks just fine. How many viewers are on the planet that actually watch a screen at 4k resolution? That would require a 120 deg viewing angle... but that is another subject. When I look at some of the best 4k movies on bluray, it makes no difference watching at HD or 4k.

Choose to render individual clips then tick the 'render at source resolution' box. Resolve will render clips at source resolution. This is the best way for generating graded VFX plates.

It will upscale. Output scaling is the last thing in the process tree.
You can change timeline resolution, but when you do some operations like node sizing don't scale. Sharpen/Soften, some FX might look not exactly the same. So it might take some manual tweaking to get it right.

Is it really worth it? Upscaling looks just fine. How many viewers are on the planet that actually watch a screen at 4k resolution? That would require a 120 deg viewing angle... but that is another subject. When I look at some of the best 4k movies on bluray, it makes no difference watching at HD or 4k.

Tell that to Netflix!