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Phoenix has explicit self-trade prevention modes at the matching-engine layer.

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Available behaviors

BehaviorWhat happens
AbortReject the self-cross instead of matching it
CancelProvideCancel the resting provide-side order on the self-cross
DecrementTakeReduce the incoming take-side quantity by the self-cross amount

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Default behavior

For the core limit and IOC builders, the protocol defaults to CancelProvide unless the caller explicitly chooses another behavior. Some specialized flows use stricter defaults. For example:
  • many SDK examples use Abort
  • TP/SL-triggered orders are designed to avoid accidental self-matching

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Why this matters

Without STP, a trader could:
  • fill against their own resting order
  • pay fees for a meaningless self-match
  • distort fill history and realized PnL

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User-facing outcomes

If a self-cross is detected, you may see:
  • an order reject
  • a resting order cancellation
  • an incoming order that fills less than its original requested size
Those are not random outcomes. They depend on the selected STP mode.