Although the number of improvements included in the new firmware versions is not overwhelming, there are several updates worth installing specifically for Cortana-based digital assistant users to perform tasks.
In the case of the Surface Pro 4, the new firmware version updates the Intel Smart Sound Technology (Intel SST) audio processor on System devices on 09.21.00.2102 which includes support for playing video in installed applications while offline.
As for the Surface Book, it offers the same program updates alongside Realtek High Definition Audio (SST) that improves Cortana speech recognition.
Firmware updates can only be ported via Windows Update to systems running Creators Update, and a restart is required to complete the installation. In addition, make sure that the battery is fully charged or that your device is connected to a charger before starting the update process.
Both the Surface Pro 4 and the Surface Book are the latest editions of the two models, although they were released in October 2015. Microsoft has planned to produce new editions of the two models.
Note that Surface Pro 5 and Surface Book 2 were expected to start in the autumn of 2016, essentially one year after the release of the first releases, but eventually their presentation was postponed until the spring of this year. The devices seem to need enough time to grow successfully.
Microsoft is expected to hold an event on 2 May but it is almost unlikely that the Surface Book 2 will be included in it.