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Every order carries a required timeInForce. It decides how your order behaves in the order book. A GTC order can still be a taker. If it crosses the book on arrival it matches immediately, and only the remainder rests.

Post-only

postOnly: true is a modifier on a GTC order, not a fourth timeInForce. It makes the order add liquidity only: if it would cross the book on arrival it is cancelled with inactiveReason: "POST_ONLY_WOULD_CROSS" instead of matching. An order that does not cross rests as usual. Because it can never take, no betting delay applies.

Which one to use

Posting orders

Build, sign and submit an order of any type.

Taking liquidity

The immediate-execution path, end to end.

Order lifecycle

PENDING, ACTIVE, INACTIVE, and every terminal reason.

Tracking your orders

timeInForce and postOnly are write-only — tag them in your own store when you post.
Last modified on September 8, 2026