Reducing Order Quantity Without Losing Price-Time Priority
Summary
This exchange API guide explains how to lower the quantity of an existing order while retaining its place in the queue at the same price. It compares an in-place amendment with cancel-and-replace: cancel-and-replace creates a new order behind orders already resting at that price, while an eligible quantity reduction preserves the original order ID and time priority. The examples illustrate this distinction with a fictional order book.
The guide also describes operational details: successful amendments appear in the response and user data stream, failed requests leave the order unchanged, and modification history can be queried. It covers client order IDs, iceberg visibility, and order-list behavior, including linked quantity handling for OCO pairs. Amendments currently carry no unfilled-order-count charge, and symbol eligibility is indicated in exchange information. The documented amendment is limited to quantity reductions; examples omit commissions, and the guide does not discuss other order changes or execution outcomes.
Key ideas
- An eligible amendment reduces an existing order's quantity while preserving its queue priority.
- Cancel-and-replace assigns a new order and loses its time priority at the price level.
- A rejected amendment leaves the original order unchanged.
- Iceberg and order-list amendments have additional quantity behavior, including linked OCO quantities.
- Supported symbols are identified through an exchange-information eligibility field.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.