In summary a useful way of thinking about the difference between new code and classic code NLP is in terms of emphasis.

Classic code emphasizes technique, mechanistic metaphors and the production of NLP technicians. It uses conscious explicit models that are often divorced from their original context. With Classic code you often hear the questions “where do I use this technique” and “how do I know which technique to use”? There is a tendency for classic code trained practitioners to try to fit clients to procedures, rather than creating interventions with clients.

New code emphasizes the relationship between the conscious and unconscious minds of the individual, their relationships with others and their relationship with the world. It works towards the personal evolution of the participant. New code promotes unconscious competence. Training drills are used in service to pattern incorporation and the development of unconscious competence. The balance between the conscious and unconscious minds is paramount. This is known as the conscious / unconscious interface.
New code is directed towards the detection and utilization of patterns in the world, with an emphasis on patterns. A new code practitioner often creates a process spontaneously in response to a particular context. In new code participants do a lot of exploration of psychological states. They learn to recognize, inventory and change states. This work connects in with the development and incorporation by each participant of a modeling state. A state of mind for modeling excellence.

Another aspect of New code is attention training (essential for modeling). That is learning where and how you place your attention, how that relates to state, perceptual position and context. My understanding is that Grinder and DeLozier developed new code as a second description of Neuro-Linguistic programming to create a system for learning NLP which is more likely to foster the development of systemic wisdom in the participant. If you want to learn more about New code read Turtles All the Way Down by Judith Delozier and John Grinder and Whispering in the Wind by Carmen Bostic St Clair and John Grinder.