If the interviewer skips fit, follow their lead. Interview formats vary by interviewer, round, and timing, and you do not need to force a behavioral section into the conversation.

The invitation may describe a general interview structure, but an individual interviewer can allocate the time differently. Your job is to respond to what is actually asked.

Fit may appear at the end, in another interview, or not at all in that session. That does not mean your preparation was wasted because another interviewer may still probe it.

Stay ready for both components, but do not interrupt the flow to ask why fit was skipped. Use the time you are given to perform well on the case in front of you. For more detail, see the case interview guide.

I would just follow the interviewer and not force fit into the session.