Quote from nononsense:
That's all I found on their website. Rather meager info.
FastPath API
The comprehensive FastPath API is easy to use. It allows for multiple connections, order placement and cancellation, order status, position, account management, balances and more. Specialized messages allow models to instantly switch routing or change strategies in response to market factors such as latency at the exchange or indications of fast moving markets. The API is Fix 4.2 compliant and available on request.
TickStream API
The TickStream API can be used to retrieve live market data including depth of book. Clients can request historical data from yearly intervals on tick-by-tick data for all US equities, options and futures exchanges. Market data is available through a multi-cast ASCII feed or a publish-and-subscribe process so clients can achieve optimal performance for their trading strategies.