In the case of position transfers, certain U.S. transferors (e.g., brokers, stock transfer agents, custodians, stock issuers) are required to provide cost basis information for covered securities to the receiving brokers, however, this information is oftentimes not sent at the time of transfer. Instead, the cost basis information is typically provided electronically via an alternative DTCC system referred to as the Cost Basis Reporting Service, although some transferors provide the information in writing via postal mail. Transferors who are required to provide cost basis information must do so within 15 days of the date of transfer and IBKR will send an electronic request to the transferor for the information if not received by the 10th day.
For information regarding how to update your cost basis information when the transferor has not yet provided this information to IBKR, see How do I update cost basis information for transferred securities?.