IBKR provides a variety of methods to assist account holders engaged in short selling with monitoring inventory levels and borrow costs/rebates. The level of detail available, the time frame covered and the manner in which the information is accessed vary by method and a brief overview of each is provided in IBKR Knowledge Base article "Monitoring Stock Loan Availability".
How do I see whether a stock is shortable via sFTP?
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Monitoring stock loan availability
How do I see whether a stock is shortable on TWS?
Is the security quantity that is eligible to short available through the TWS API?
Why do I receive a notice of a potential buy-in of my short position when Short Stock Availability shows shares available to borrow?