To sum it up, this is a company with very high standards of BS.

• I completed my OO round in 30 minutes. He did not have anything to ask, then he started talking about their open-source projects.
• I did the code in 20 minutes while explaining my process line by line, then another 10 minutes for debugging and covering corner cases, after which he said, "I think the code is perfectly fine and would work in all scenarios." Then he told me about his team.
• The system design was clean and readable, to which I got feedback from the interviewer that, "This is a really good design and it would scale really well."

Still rejected. The reason they gave me was hilarious: "Your code (Interview 2) was not fast enough (I did it in O(n). If the interviewer can do it in less time, then he should quit Hubspot and open his own startup)."

Coding round: Hit API, get JSON, manipulate it, and hit again to get a 200 response.