As of the latest version of Java, OpenJDK is equivalent to Oracle JDK, and they'll release new versions every 6 month. However, there won't be any security updates or bug fixes to OpenJDK versions from Oracle after 6 months. There's a few groups that plan on maintaining patches beyond that period, but most options involve paying someone (including Oracle).

It's mostly just about enterprise distribution, rather than any differences in the JDK. Updating major versions every 6 months is risky, not having security updates is more risky, and no one likes paying money for something that they've been getting for free.

So far this seems like the simplest and cheapest way of getting long term security/bugfix updates for the JDK, especially if you're already running Amazon Linux. We've been evaluating the options in my team recently and hadn't come to a decision beyond "update to Java 11 and see how it goes after that". This pretty much solves our problems.

I would have preferred to see Amazon partnering with Red Hat or other open source groups on maintaining one well supported OpenJDK, but at least as it's all open source, patches should make their way to all versions.

It is openjdk. Amazon intends to package it nicely and support their releases with backports for security fixes.