The -u option lists all installed matching packages that have newer versions available. The number of packages that have newer versions available might be larger than the number of packages that could be updated in this image, as demonstrated in Newest Packages. Packages can be updated only to versions allowed by the constraints imposed on the image by installed package dependencies and publisher configuration.
$ pkg list -u '*toolkit' NAME (PUBLISHER) VERSION IFO system/dtrace/dtrace-toolkit 0.99-0.175.2.0.0.34.0 i--