Sorry, I meant committers. I'm asking since the link you posted talks about open source events and has some job postings. I was looking for actual contributions by Amazon employees.

There's far more listed there including entire projects, repos, videos and several blog posts detailing their contributions, including one describing what they're doing for Cassandra: https://aws.amazon.com/blogs/opensource/contributing-cassand...

Amazon, Microsoft, Google, Oracle, IBM and others are all major contributors to open-source software.