OpenAI seems to be a heavy user of Kafka, in their last Kafka conference - Confluent Current (previously called Kafka Summit) they shared their Kafka usage grew... 20x in the last year[1][2]

I watched the talk live. They didn't exactly share what it's used for, but it was clear it was ubiquitous and that they invested heavily in a) availability, because it was critical for them and b) simplicity, because they wanted to onboard as many teams on it as possible

1 - https://x.com/BdKozlovski/status/1924838299706790307 2 - https://current.confluent.io/archive/2025/london (but it's contact-walled)