Hi @elliotmiller18 and thanks for your patience!
I wanted to let you know that we heard your feedback, and we’ve made an update to the documentation:
“Conversations inbox and messages APIs”.
I can confirm that the maximum limit is 500.
Thanks again @elliotmiller18 for sharing your feedback with us. It helps improve HubSpot for our whole Community 
Have a fantastic weekend and I look forward to seeing you around the Community!
Bérangère