the last word in (something)
The most modern or advanced version of something. It may not look like much, but I can assure you that this machine is the last word in neural imaging. They claim to be designing the last word in drone technology.
the last word in something
If you say that something is the last word in luxury, comfort, or some other quality, you mean that it has a great deal of this quality. The spa is the last word in luxury and efficiency.