FX trades less than 50,000 (or 30oz gold) are bundled together until they reach 100,000. Trades above 50,000/30oz will go directly to the market.
The price that is given to clients is always derived from our liquidity providers. The trade is executed using Global Prime's FIX engine 'Skout' based on these prices. Execution speeds for Skout are usually around 1ms. There isn't an artificial delay on fills as is the case with b-book brokers trying to emulate real market execution.
The 50k internalization and 100k thresholds are the lowest reasonable size to prevent small tickets hitting multiple LPs: increasing trading fees, significantly. The thresholds are trading volume, liquidity provider and prime broker dependent.
50k and 100k are geared towards Global Prime mitigating small ticket fees. We still pay these fees and they're still relatively high. The small ticket aggregation reduces the fees to a level that makes our dealing model more viable.
More information here: https://www.globalprime.com/best-execution/