The header docs in BAAppExtensionInfo.h reference this key: /// @brief The number of bytes remaining that can be scheduled if the total download size of optional assets is restricted. /// @discussion When a download is restricted, your extension can only schedule up to its `BAEssentialDownloadAllowance` /// defined in your app's `Info.plist`. This result tells you the number of bytes remaining that can be scheduled /// before the application is launched. Once the application is launched, this restriction is removed. /// @result The result is `nil` if downloads are not restricted. It returns a valid number with the remaining available download size otherwise. @property (readonly, strong, nullable) NSNumber *restrictedEssentialDownloadSizeRemaining Judging by this, it seems like this key indicates the total number of bytes of downloads that your app deems as essential to its operation. Hopefully we get clarification from Apple on this soon given it's a hard requirement.