Think in terms of interview conversations rather than just round labels. A first round may contain two separate interviews, and a final round may contain another two or more, depending on the office and role.
The exact structure varies, but the case-interview rounds overview shows the common pattern and what usually changes between stages.
Prepare as if every interviewer is an independent evaluation. One strong conversation does not let you coast through the next one, and a different interviewer may emphasize different parts of the case or fit discussion.