Sign in to Superthread (or create an account for free)
Upgrade your plan by going Settings > Workspace > Plans
Click the 'Change plan' button on the 'Pro' plan.
Enter the code TRELLO-WELCOME at checkout (no CC required).
You now have Superthread Pro, for free, for life, for your whole team (and any team members you add in the future).

Code: TRELLO-WELCOME