Do the new character and relationship features cost extra AI usage?

Almost nothing in normal writing. Character depth, relationships and arc milestones travel inside the same compact story-bible block BookyAI already sends with each chapter, under a strict size budget — chapters cost roughly the same as before. The only extra AI requests are actions you trigger yourself: "Extract from manuscript" (one request), a character portrait (one image request), and the Consistency check (one request per finished chapter). Nothing runs in the background without you.