Ask HN: What to show to get an initial market validation?

I'm building a service to be consumed as an API which relies on some deep learning models that I've been developing. It's a Computer Vision related project, the idea is to extract features from images to be used from the customers (mainly CRM's).

The current code takes a lot of time to run and I would need a considerable amount of time to optimize it. This is a side project right now, so I'm trying to optimize the time I dedicate to it.

I've the possibility to get a meeting with two or three prospects (it'll be B2B business) and I'm thinking about what (and when) to show to them in order to make an initial market validation.

1) Show them the program output from a computer terminal: we take some images from the web and I show them what would be the result if they use the service.

2) Show them only a presentation with the current and future features.

3) Wait and spend X time (something like two months) developing a functional API and then get the meetings to show them the working API.

What would you do if you were me?