Thank you for this clarification.
Let me quote the Apache Tomcat Website to answer your questions:
Apache Tomcat 9.x is the current focus of development, it builds on Tomcat 8.0.x and implements the current draft of the Servlet 4.0 specification and will also implement the JSP 2.4?, EL 3.1?, WebSocket 1.2? and JASPIC 1.1 specifications once work starts on updating those specifications for Java EE 8.
Apache Tomcat 8.x builds on Tomcat 7.0.x and implements the Servlet 3.1, JSP 2.3, EL 3.0 and WebSocket 1.1 specifications.
Apache Tomcat 8.5.x supports the same Servlet, JSP, EL, and WebSocket Specification versions as Apache Tomcat 8.0.x. In addition to that, it also implements the JASPIC 1.1 specification. There are significant changes in many areas under the hood, resulting in improved performance, stability, and total cost of ownership.
I don’t know the timeline for 9.x, but it will require Java 8 whereas 8.5.x still runs on Java 7.