FIX FAST

The key difference between FAST and FIX is that FAST employs binary encoding and compression to reduce the size of FIX messages, which employ plaintext encoding.

Compared to FIX, FAST achieves smaller messages, faster encoding and decoding, and lower serialization latency. However, unlike FIX messages, FAST messages are not human-readable. It will also be generally harder to implement an encoder or decoder for binary encoding formats.

A popular implementation of FIX/FAST can be found in the legacy CME data feed, which existed before CME adopted Simple Binary Encoding (SBE) in its MDP 3.0 feed.