Amian Patnaik provides an overview:
The Kappa Architecture, introduced by Jay Kreps, co-founder of Confluent, is designed to handle real-time data processing in a scalable and efficient manner. Unlike the traditional Lambda Architecture, which separates data processing into batch and stream processing, the Kappa Architecture promotes a single pipeline for both batch and stream processing, eliminating the need for maintaining separate processing pipelines.
What’s interesting to me is that Lambda, an architecture which was an explicit product of its time (in the sense that it was a compromise architecture trying to do two things, the combination of which limited hardware and tooling didn’t allow), is still thriving today. Kappa, meanwhile, isn’t an architectural style that people throw around a lot anymore, at least in the circles I run around in.