Interactive Brokers.
The institutional-grade execution layer most custom trading systems are actually wired to.
Overview
Interactive Brokers offers global multi-asset access — equities, options, futures, FX, bonds — with margin and commission economics that scale from individual quants to funds, and the deepest API surface in retail-accessible brokerage: the TWS API, FIX connectivity for institutional flow, and a REST Client Portal API. It is the default answer to 'where does the custom system actually execute?'
Where it fits
- Systematic traders who need one account with global multi-asset reach and programmatic control.
- Funds and prop desks wanting FIX connectivity without a prime-brokerage minimum.
- Long-running automated systems that require battle-tested, documented API behavior.
Constraints to weigh
- The TWS API's session-and-gateway model adds operational overhead (gateway uptime, session resets) that pure-API brokerages avoid.
- Market data subscriptions are à la carte and add real cost at scale.
- Support is institutional in tone; expect documentation-first troubleshooting.
In an agentic workflow
For autonomous execution, IB's granular permissioning, per-order risk controls, and paper-trading environment map cleanly onto a staged agent-deployment path: paper → constrained live → scaled live, with kill-switch semantics enforced at the brokerage layer as a backstop to platform-level controls.
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