Seeing a car driving through urban traffic with no one in the driver's seat might give the impression that Waymo has already reached the highest level of automation. From the passenger's perspective, there is no steering wheel, no monitoring and no need for human intervention. The vehicle handles the entire trip on its own.
However, under the SAE (Society of Automotive Engineers) driving automation framework, that capability is still Level 4 rather than the highest: Level 5. The key distinction is not how "independent" the driving appears in practice, but where that independence is permitted to exist. At Level 4, the system can fully handle the driving task without human intervention, but within a defined set of conditions and locations. Level 5 eliminates those limits entirely.
Strictly speaking, it is the Waymo Driver, the company's automated driving system, that is classified as Level 4. Safety research published by Waymo describes it as an SAE Level 4 automated driving system, and that classification explains why an empty driver's seat does not automatically make a Waymo Level 5.
There are six SAE automation levels in total, numbered 0 through 5. The National Highway Traffic Safety Administration (NHTSA) begins its breakdown at Level 0, where the human performs all driving, even if safety systems can briefly intervene. Level 1 can continuously assist with steering or acceleration and braking, while Level 2 can handle both simultaneously. In each case, the driver remains responsible for the vehicle.
Level 3 changes who is driving. The system can handle the entire driving task under certain conditions, but the human must be available to take control when requested. At Level 4, that requirement disappears. Once the automated system operates within its intended conditions, the occupants are passengers rather than backup drivers.
That is why Waymo can describe its service as completely autonomous without claiming it is SAE Level 5. Its cars can complete trips with no one sitting behind the wheel, but that capability still has defined operational limits.
Those limits are generally described as an Operational Design Domain, or ODD. In simple terms, the ODD defines where and under what conditions an autonomous driving system is designed to operate. That can include geography, the types of roads it is designed for and the weather conditions it can handle. The SAE defines it as the set of conditions for which an automated driving system is designed, and Level 4 systems are expected to handle driving on their own within those limits.
At Level 4, the system handles the complete driving task within its ODD. Level 5 eliminates that limitation: the NHTSA describes it as operating universally rather than within limited service areas. So Level 5 is not about a car being "more autonomous" during a particular manoeuvre. A Level 4 Waymo already handles steering, braking and decision-making on its own when operating within its domain. The difference is scope, not who is responsible for the driving.
That is why Waymo can continue improving its system and remain Level 4. For example, Waymo claims that its sixth-generation Driver has expanded capabilities for more diverse environments, including extreme winter weather. Expanding into new cities or types of weather makes the system more capable, but as long as it continues operating within defined limits, it remains Level 4 rather than Level 5.
Expanding a Level 4 system gives developers boundaries around the problem. They can define where the system must operate, identify the conditions it needs to handle and test its behaviour against scenarios relevant to that domain. Eliminating those boundaries increases dramatically what must be considered.
That is already difficult at Level 4. In its 2026 research on collision avoidance testing, Waymo noted that evaluating a Level 4 system is complicated by the potentially enormous number of operational scenarios in which a dangerous situation can develop. Its methodology identifies potentially dangerous scenarios using human driving data, data from Waymo's automated driving tests and expert knowledge.
Weather offers a concrete example of those boundaries. In May 2026, Waymo encountered flooded roads in Atlanta and San Antonio, leading the company to suspend or restrict some operations while working on improvements.
There is no reliable countdown to when Level 5 will arrive. The NHTSA currently says that Level 5 technology is not available in vehicles for consumer purchase, and the SAE levels describe capabilities rather than a development roadmap.
