Wow, congrats on getting to the final round! 

Here are a few points to have in mind for it (i.e., how is it different from previous / first round):

1. Work on the feedback provided in the previous rounds. Most firms communicate the feedback from the previous rounds to the final interviewer. It's important then to show the final interviewer that you have a growth mindset and are reactive to feedback. This matters immensely. Make sure you are clear on your development areas and that you get the right support to polish them before the final interview.
2. Expect less structure. Senior interviewers already have the confidence that you are a decent candidate, your skills having been already vetted by their younger colleagues. They are rather more interested in your as a person and your way of thinking. So they might present you with an unusual case, or one that is created on the spot or no case altogether. Expect anything.
3. Focus on excellent communication. Senior interviewers care a lot about how clearly you communicate and how you manage to forge a connection with the interviewer. It's important to be top-down and concise as much as possible with your answers, while allowing the conversation to flow in a natural way.
4. Put yourself in their shoes. The one question senior interviewers are asking themselves throughout the interview is what will happen when they'll put you in front of a client they've groomed for years? Make sure that even based on this first impression you seem somebody who can be trusted and who can work with any client regardless of how difficult they might be.

Best,
Cristian