Now that I’m sending keys out to press/media/influencers, I wanted to check if a Steam key had been activated or not, but I didn’t know how. I read the Steamworks documentation and found a section titled “Querying Keys”: https://partner.steamgames.com/doc/features/keys#10

Apparently, you can look up individual keys one by one to check their activation status at the following page: https://partner.steamgames.com/querycdkey/cdkey

On the Steamworks interface, it can also be found under Tools > Query Steam Key. I am unable to find a page which lets me query multiple keys at once.