I wonder where Solaris is still actively being deployed and used.

I think that OpenIndiana is where those with general interest in Solaris on x86_64 should go.

https://en.wikipedia.org/wiki/OpenIndiana

SmartOS, for example, is a more specialized application of the scions of OpenSolaris.

Here is a list of other distros that originated from the Illumos efforts after OpenSolaris was terminated:

-DilOS, with Debian package manager (dpkg + apt) and virtualization support, available for x86-64 and SPARC.

-NexentaStor, distribution optimized for virtualization, storage area networks, network-attached storage, and iSCSI or Fibre Channel applications employing the ZFS file system.

-OmniOS Community Edition, takes a minimalist approach suitable for server use.

-OpenIndiana, a distribution that is a continuation and fork in the spirit of the OpenSolaris operating system.

-SmartOS, a distribution for cloud computing with Kernel-based Virtual Machine integration.

-Helios, a distribution powering the Oxide Computer Rack.

-Tribblix, retro style distribution with modern components, available for x86-64 and SPARC.

-v9os, a server-only, IPS-based minimal SPARC distribution.

-XStreamOS, a distribution for infrastructure, cloud, and web development.

https://en.wikipedia.org/wiki/Illumos#Distributions

Edit: From this blog entry, this is suspicious: "the committed support for Oracle Solaris until at least 2037" - does Solaris have a 2038 problem?

As a former SUN sysadmin/netadmin (from SunOS 4.1.4 days), I vaguely remember the Solaris releases after 2.5.1, maybe to another re-version/branding called Solaris 7, maybe? And then not paying any attention after Oracle absorbed it. I was honestly surprised enough by this headline to click TFA, simply because I did not think Solaris even existed anymore.

it's mostly OmniOS/SmartOS and other Illumos (descendant of OpenSolaris) distributions. All the Solaris 11 deployments i was aware of in mid-late 2010s are now either migrated to some sort of container setup of running on OmniOS.

One of Australia's bigger universities still had a Solaris server 15 years ago - no idea if it's still in use though.

A few places, Fujitsu also has Solaris servers, and if you care about security, Solaris SPARC is the only production UNIX with hardware memory tagging in active use since 2015.

My employer uses ZFS under AndrewFS (aka AFS) and I would bet dollars to donuts that the OS is Solaris.

I recently saw it on a big European bank. The Oracle version.

An of course Oxide is still very active in developing the open source version. They develop upstream first.

Solaris proper, not Illumos?

I think Oxide Computer uses it.