Quick definition
The process by which the seller of an option is required to fulfill the contract — delivering shares on a short call or buying shares on a short put. Assignment is the moment options become stock.
Who gets assigned and when
For US equity options (American style), assignment can happen any business day the option is in-the-money, though it most often occurs at expiration or the day before an ex-dividend date for ITM calls. Traders holding short positions have no control over the timing — the OCC's assignment process is random within the pool of short positions on that strike.
It is a feature, not always a failure
Some strategies actively want assignment — the cash-secured put and covered call, for instance, treat assignment as a good outcome that establishes or unwinds a stock position at a chosen price. Other strategies, like credit spreads, treat assignment as an operational event to be managed. Panic-selling after assignment is one of the most common expensive mistakes retail options traders make.
How Treeova uses it
Treeova's agents track assignment risk explicitly — a short leg that goes deep ITM near expiration is flagged before assignment happens, giving the agent time to roll, close, or accept the resulting stock position with intent. The Adaptive Risk Engine also models post-assignment margin impact so the agent doesn't wake up to an unexpected buying-power call.