IBKR will update and apply new tax treaty rates as they are effective.  However, be aware that there is often a delay between the announcement of new tax treaties and the effective date for withholding changes by brokers.  Until the effective date, IBKR must continue to withhold at the existing statutory rate (or old treaty rate).

Circular 230 Notice: These statements are provided for information purposes only, are not intended to constitute tax advice which may be relied upon to avoid penalties under any federal, state, local or other tax statutes or regulations, and do not resolve any tax issues in your favor.