Standardizing how requests (and responses) are made is key to allow any two entities to “speak” to each other. While OpenRTB exists as a standard for transacting ad inventory in an RTB transaction, there are a number of other scenarios where no standard exists. For example, making a subsequent request for ad creatives (whether in programmatic or direct) was never standardized in the same way. SSAI is another area with new use cases that require standardized ad requests. While VAST 4.x partially addressed these by specifying VAST request guidelines and macros, it usability and scale are limited by some technical constraints such as URL length limits for HTTP GET requests.
CATS aims to address these gap by defining an ad request standard that can be used for both RTB and non-RTB use cases, while building on top of existing specifications like AdCOM.
Some key points about CATS (more details in the spec) –