In the Content API for Shopping, Merchant IDs are now 64-bit signed integers. Applications that integrate with the Content API must be able to handle ID values in that range.

Historically, Merchant IDs in the Content API for Shopping were within the maximum value of a 32-bit signed integer, but have recently exceeded this range. In order to avoid any issues, please make sure your applications are fully compliant with IDs within a range of 64-bit signed integer values.

If you have any questions or concerns, please don't hesitate to contact us via the forum.
Benji Rothman, Content API for Shopping Team