Looks like they're starting a Pro version that requires signup/payment.
I suspect you misunderstood. It's Open Source, at least the free version.
Or maybe I'm missing something?
There's a free trial that lasts 2 weeks. After that I think it's paid.
Not exactly. The paid editions have free trials, but there's also a community edition that is free. However, it's pretty difficult to figure out what exactly is supported in the community edition. There's a whole list that mention various AWS services are only supported in "PRO", but I don't know if that means that free support might come later in community.
All the basic stuff is in the community one. Certainly lambdas are.