If you purchased Subnautica through Arc, and would like to activate it on Steam, please follow the steps below:
- Open the Steam client
- Click Add A Game in the lower-left corner followed by Activate a Product on Steam...
- Follow the remaining on-screen prompts to activate Subnautica on your Steam account
When Subnautica is purchased through Arc, the Steam key should be delivered to the email address registered to the Arc account.