The JSR 374 Expert Group has just posted the first Early Draft of the 'Java API for JSON Processing specification version 1.1' also known as 'JSON-P 1.1 EDR1'.
This is the first cut of the JSON-P 1.1 API that is slated for inclusion in Java EE 8. The scope of any specification might (slightly) evolve, things might be removed and/or added. For example, the support of JSON Merge Patch wasn't originaly planned when this JSR was started but it is now part of EDR1. On the other hand, support for 'Big JSON' is still being discussed but again, it's a draft, the API will still evolve.
At this stage, it is important that you read the Javadoc and try the API to provide feedback. There are still plenty of time to adjust things so feedback is really important. To easily get started on JSON-P 1.1, you might want to check those resources.
On a practical note, the Javadoc *is* the specification so don't look for a PDF specification document. The Early Draft period will be closed on October, 2. In the meantime, the EG is eagerly awating your feedback! As usual, comments and feedback should be sent to the JSON-P users mailing list.