It comes down to time. It is only a few months work to replace the "control" heuristics with a NN. It is years or decades to produce one end-to-end NN that does everything. Some of that computer science doesn't even exist yet.
Instead, they'll have all the foundations they've built already, and the smoothness and control capabilities of a NN. This needs to ship by end of year, get Europe and China running FSD, then they move on to HDW 4, all BEFORE the vast majority of DOJO compute is online.
No way they redo everything. Elon is just talking out his ass about a rewrite of everything. They physical are not capable of doing that.
There's three main NN functions:
- Perception (that's "Tesla Vision")
- Planning (that's mostly the "language of lanes" based on LLMs tech), and
- Control (that was 300+K lines of C++ code, with v12 it will be a NN driving.
If an analogy helps you understand things better, think of how a rally race car team works:
there is a Driver and a Navigator. The Navigator looks at the maps, know where they're going, and follows the progress, giving timely instructions like turn left, get in the center lane, slow down dumbass.
Passing these instructions takes a certain amount of time, the Navigator must give the Driver time to react, and to make things happen. But it is the driver that twitches with the steering wheel when a big damn rock appears over the crest of a hill, he doesn't wait for the Navigator to tell him he needs to react. Oh, and they both have eyes (Tesla Vision), it's just their roles and responsibilities are separate, but they work as a team. The driver in realtime, doing the twitchwork, the navigator following progress closely and giving instructions, while gathering information from maps, signs, weather, road conditions, traffic-alerts, messages from passengers, emergency vehicles and flagmen, ...
Should I post a video here?