I think this might be related to the warframe ARG, they added some text to the steam listing saying:

ᴀɴᴏᴛʜᴇʀ ʀᴇᴡᴀʀᴅ, ᴄᴏᴜʀᴛᴇꜱʏ ᴏꜰ ᴛʜᴏꜱᴇ ᴄʟᴇᴠᴇʀ ᴛᴇɴɴᴏ ꜱᴛɪʟʟ ʜᴀʀᴅ ᴀᴛ ᴡᴏʀᴋ. †hê §ïgñål ï§ §þrêåÐïñg

Less related, but Unreal Tournament and Unreal Gold are also free. https://dormi.zone/post/3413855

Kind of importantly, this is the first time it’s been legally available in Australia since it wound up abandoned in a legal grey area and none of the rightsholders could be bothered fixing the Steam listing.