JDK 12 [Java SE 12 Platform (JSR 386)] is still in Rampdown Phase 1, but initial work on JDK 13 [Java SE 13 Platform (JSR 388)] has already begun. Draft 26 of the Java SE 12 specification was announced approximately 10 hours before Draft 2 of the Java SE 13 specification was announced.
There are already early access builds of JDK 13 available for Linux, macOS, Windows, and Alpine Linux. As of this writing, the current JDK 13 early access build is #2 (3 January 2019). The JDK 13 Early-Access Release Notes do not yet contain anything of significance.
There are ten change sets associated with Build 2 and another ten change sets associated with JDK 13 Early Access Build 1. There are 33 issues addressed with that build (688 total bugs associated with JDK 13 for "build fix" as this writing).
The temporary home of the Javadoc-based API documentation for JDK 13 is also available at https://download.java.net/java/early_access/jdk13/docs/api/.