> How stable is beowulf? Is there people using it in production?

It is stated on https://devuan.org/os/releases:

Beowulf -> In development
I suppose it is equivalent to "testing".

"testing is where the next stable suite is developed. Software is
usually more up-to-date but there may still be issues. testing becomes
stable “when it is ready”."

It is thus technically "not ready" - yet. The dev team released Ascii
2.1 recently, which concurs with the table in page linked above.
Follow announces for when that will change.

I suggest you read the changes:
https://www.debian.org/releases/stable/amd64/release-notes/ch-whats-new.html

-----

On a personal note, I switched from Ascii to Beowulf almost exactly a
month ago. Hard to get proper feedback with such a small hindsight, but
here a couple points:
- So far, no major problem
- A myriad of package default configuration having changed (hence a lot
of diff to do to cook modified configuration files on top of the new
formats) -- nothing unusual here, though
- AppArmor!
(https://www.debian.org/releases/stable/amd64/release-notes/ch-whats-new.html#apparmor)
If you run a nameserver daemon, the corresponding AppArmor configuration
will most probably not be activated: none of mine was.
It seems also to be a pain with namespaces (containers) requiring
elevated privileges ie for debootstrap (cf.
https://stackoverflow.com/questions/26406048/debootstrap-inside-a-docker-container/45661089#45661089)
- Even though I use scripts to automatically save/restore ip(6)tables
rules on up/down, I ended up having my rules cleared through initial
reboots. No precise idea on why.
I suggest you always keep a manual save of them somewhere.

> How to I upgrade from ascii to beowulf?

As usual with APT.
If you are unsure, you can follow Debian's guide
(https://www.debian.org/releases/stable/amd64/release-notes/ch-upgrading.html).

The tutorial uses apt. Some feel more confident with the lower-level,
original interface apt-get.

HTH,
Bernard Rosset
https://rosset.net/