Screencast / screen record in 4k resolution?

I saw a few screencast on YouTube that were in 4k resolution which is awesome by the way.

I did a quick web search and found that there are a lot of screen-casting software that record in 4k. Camtasia being one of them.

I was wondering how can i record in that resolution?

Do i need to buy a monitor that supports 4K resolution to record in 4k or will i be able to achieve it by just upgrading my graphics card.

Kindly do guide me in this regard.

Thanks