That's my line of thinking as well. Not arbitrage, but perhaps trading at a frequency not profitable on other retail platforms (and obviously a couple orders of

That's my line of thinking as well. Not arbitrage, but perhaps trading at a frequency not profitable on other retail platforms (and obviously a couple orders of magnitude slower than HFT). Some things you could perhaps do on Robinhood that aren't feasible with other retail brokers include: a) Tiny, tiny position sizes, even on small accounts. 1% position sizing? What about 0.1%? b) Not incurring a transaction fee if your system decides to immediately exit a position after entering it due to adverse movement in the time it took to fill the order. Potential concerns might be: 1. Order execution speed. Sending orders to retail brokers via the internet can only be so fast, but it'd be interesting to benchmark Robinhood vs IB for example. 2. Order execution capability. There's no public API, just Quantopian integration. My other post in this thread touches on that. 3. Order execution quality. RH sells order flow. How much this matters is probably beyond my knowledge. I'm inclined to think that it wouldn't matter too much, and is more likely to adversely affect competing HFT firms who are in competition against the order flow buyer(s) than it would people trading at even the upper bounds of retail frequencies. 4. How many trades is too many? Will Robinhood shut you off at some point? Another post suggested RH is paid a fixed amount per share in their order flow dealings, so if that's the case then maybe Robinhood wouldn't care. Certainly as soon as they have a public API there's going to be people making a lot of trades, barring any artificial limitations. Of course, if your margin account balance is below $25,000 you'll be subject to pattern day trading restrictions and unable to execute such a system since Robinhood is purely stocks. I loathe PDT rules to the core of my being and believe they actually increase risk for short-term traders, but that's a rant best saved for another time.