There are two versions of Tesla Autopilot across all Tesla vehicles (S, X, and 3):
1. Original AutoPilot, known as AutoPilot, AP, or AP1.
- Based on the EyeQ 3 chip manufacturered by MobileEye.
- Single camera facing forward + radar facing forward
- Maintans lane with autosteer and following distance with traffic-aware cruise control (TACC)
- Can change lanes with turn signal stalk.
- Can read speed limit signs and display the speed limit in the instrument cluster
- Can display cars in adjacent lanes in the instrument cluster, can classify vehicles as "car", "large truck", or "motorcycle" and display the corresponding graphic in the instrument cluster.
- Hardware installed in Model S vehicles manufactured in September 2014 and later.
- Autosteer software was not activated until October 2015
- Current capabilities represent the maximum that it will ever be able to achieve
- Software is mature, well-controlled, deliberate and methodical, but not perfect. Autosteer can steer out of the lane on occasion, usually in response to less-than-perfect lane lines or other pavement markings.
- Only installed in Model S and a few early Model X's.
2. New AutoPilot, known as Enhanced AutoPilot, EAP, AP2, AP2.0 or AP2.5.
- Based on the NVidia PX2 chip and Tesla in-house development.
- 8 cameras -- 3 facing forward (wide field, standard, and long-range), 4 side cameras, 1 rear camera, + radar facing forward.
- Maintains lane with autosteer and following distance with traffic-aware cruise control (TACC).
- Can change lanes with turn-signal stalk.
- Will be capable of lane change and pass without driver input, navigation from freeway to freeway on its own (not yet implemented).
- Will be capable of full self-driving (not yet implemented)
- Cannot currently read speed limit signs, speed limit is displayed on the instrument panel by database lookup.
- Cannot currently display cars in adjacent lanes in the instrument cluster -- displays cars ahead of you in your lane only. Cannot currently classify vehicles and display different graphics -- all vehicles are displayed as cars.
- Many more capabilities to be added through software.
- Hardware installed in Model S vehicles manufacturered in May 2016 and later.
- Software was not activated at all until February 2017.
- Software was notorious for nearly-useless autosteer capability when first released, but the software update released in March 2018 brought the autosteer accuracy and control to a level that exceeds AP1 capabilities.
- Installed in all current-production Model S, X, and 3 vehicles.
- Slight difference between AP2.0 and AP2.5 -- AP2.5 has one extra NVidia PX2 chip that may be needed for the full self-driving. If the AP2.0 cars cannot perform full self-driving without the extra chip, they will get retrofitted to AP2.5.
Many comparisons you are reading are from Model S owners who just bought a 3, and are comparing their S with AP1 to the 3's capabilities with AP2. The car model makes no difference here, the comparison is between AutoPilot versions. They could just as easily be comparing an early Model S to a later Model S.
History: AutoPilot 2 was released well before it was ready. The reason for this was a falling out between Tesla and MobileEye. Tesla originally intended that AP2 cars were going to have the MobileEye EyeQ3 chip installed side-by-side to the NVidia PX2 chip while AP2 was in development. Those cars would use the MobileEye chip and run on AP1 software until AP2 was ready, and then a software update would change those cars to run on the NVidia PX2 chip and AP2 software. This way, those buyers would have mature, working AutoPilot until AP2 exceeded those capabilities.
However, MobileEye and Tesla could not come to a licensing agreement (supposedly MobileEye wanted access to Tesla's collected technical and mapping data, and Tesla didn't want to give it to them). Because of this, MobileEye refused to supply any more chips, and the AP2 cars were then produced and sold without the MobileEye EyeQ3 chip installed. This forced Tesla to very quickly try to develop AP2's software and it was released well before it was ready.