React 16.0 was released with an update to the React core algorithm. This new core architecture is named “Fiber.” Facebook has completely rewritten the internals of React from the ground-up while keeping the public API essentially unchanged; in simple terms, it means only changing the engine of a running car.
With this release, some new features are also added, like Asynchronous Rendering, Portals, Error Boundaries, Fragments (i.e. return array of elements). Incremental rendering is the headline addition to React, which adds the ability to split rendering work into chunks.