Is there Ubuntu Unstable/Development, like Debian Sid (Unstable)?

I'd like to install such Ubuntu that it has always most recent APT packages. For example if new CLang is released then I want to have it in my Ubuntu in one or two weeks.

Is there anything in Ubuntu like Unstable or Development version (same like Debian's Sid) that updates APT packages very often?

Also very important - how can I install it? Where to download? I see on this page download links to versions 20 and 21 but both are not Unstable/Development versions as I understand.

Basically all I really want is just a web link for downloading some magical Development/Unstable Ubuntu as .iso file that I can install on my PC.

You can try great tool from Martin Wimpress.

The tool is named rolling-rhino and placed at GitHub:

Rolling Rhino is a simple tool to convert Ubuntu Desktop, and the official desktop flavours, that has been installed from a daily image into a "rolling release" by opting into and tracking the devel series.

There is no 'rolling' development version like Sid is.

You will need to keep upgrading/installing the in-development releases (right now it's Impish 21.10) during the dev cycles to get the 'latest development' track. There's no singular name like sid or Unstable in Debian to constantly track 'development'.

However, there is no 'magical' way to continue to track the development or unstable branches after a release is complete - except to 'upgrade' to the development release via do-release-upgrade -d on that system. However, that isn't guaranteed to work, so you'd have to do a reinstall with the ISOs for that development release to guarantee you're on that devel track, and repeat the same behavior every time a new release is being developed.

Sort of....

Most Ubuntu deb packages merge from Debian Testing (there are exceptions) twice each year, so there is no equivalent of Sid/Unstable.

Ubuntu is a distro that is designed for easy install and safe use by non-experts and beginners. It would be foolhardy to tempt (mislead) those users with a pre-release link on the main download page.

However, pre-release images DO exist -- any search engine will lead you to them at https://cdimage.ubuntu.com/daily-live/current/. Try it.

As with Debian Testing, be aware that there are still rough edges -- that's why it's PRE-release. We encourage users with the skills to properly report bugs to test their workflows and hardware and favorite applications, and to file bugs so we can get those fixed before release. Bug reports with patches are even more welcome.

• AskUbuntu does NOT provide support for pre-release versions of Ubuntu.

Understanding the six-month-long development cycle of Ubuntu is a prerequisite for safe use of pre-release versions. If you don't intend to do proper testing (and file bugs), then pre-release may not be for you.

You can download version 21.10 which is currently under development here.