From the announcement blog post: Transit is self describing using tags, and encourages transmitting information using maps, which have named keys/fields which

From the announcement blog post: Transit is self describing using tags, and encourages transmitting information using maps, which have named keys/fields which will repeat often in data. These overheads, typical of self-describing formats, are mitigated in Transit by an integrated cache code system, which replaces repetitive data with small codes. This yields not only a reduction in size, but also an increase in performance and memory utilization. Contrast this with gzipping, which, while it may reduce size on the wire, takes time and doesn't reduce the amount of text to be parsed or the number of objects generated in memory after parsing. - http://blog.cognitect.com/blog/2014/7/22/transit http://blog.cognitect.com/blog/2014/7/22/transit