The Upspin.io project site explains the project's focus:
Upspin is an experimental project to build a framework for naming and sharing files and other data securely, uniformly, and globally: a global name system of sorts.
It is not a file system, but a set of protocols and reference implementations that can be used to join things like file systems and other storage services to the name space.
Performance is not a primary goal. Uniformity and security are.
Upspin is written in the Go language and does make use of FUSE. The code can be found on GitHub.
More details on Upspin can be learned from today's announcement on the Google Security Blog.