I am not surprised they haven't made an API public yet. Looking at how razor-thin their operational margins have been on IT and financial fronts, any hypothetical added load from traders trying to algorithmically hammer some API is probably going to wind up in disaster.

I cannot speak for all of the engineering that goes down at Robinhood, but the way their web-based trading interface performed for me was regrettable at best. Never was able to load my history in that interface without my browser getting javascript timeout warnings. Always had to go back to my phone to see what dividends I got paid out. This sort of problem, which strongly-encouraged me to switch to a different broker, does not give me much confidence that other areas of engineering at Robinhood are handled much better.