What are credits and what uses them?

Credits pay for the AI work you ask for. Messages on paid AI models cost credits per reply — a little more as a conversation grows, and at most the price of the Memory you chose. The Thinking option, where the AI model plans before it replies, adds a small amount only when that planning actually happens. Creating an AI character with AI costs whatever the Fast or Slow card says. Free AI models and Manual mode cost nothing, and reply suggestions are always free. Your balance is in Usage, and a price is always shown before you commit to it.