EpiStellar subtype, Hot, dark worlds with temperatures between 800 Kelvin and 1400 Kelvin; these fall in to the ancient Sudardsky classification as Class IV worlds, and are often characterised by an excess of alkali metals in the atmosphere.
Hyperthermal subtype: Very hot worlds with temperatures above 1400 Kelvin (Sudarsky Class V worlds). These worlds are often bloated by heat expansion and may be losing atmospheric gases quite rapidly. They are distinguished by clouds of silicates and metals in the upper atmosphere, and considerable thermal emission from the dark side. Most hot neptunes of this kind are tidally locked.
Some hot neptunes have large, dense, rocky cores, and are much smaller than gaseous planets of a similar mass. Hyperbarian worlds of this kind have high gravity, and generally have a dense but compact atmosphere. These dense planets may look quite similar to other hot neptune worlds, apart from their smaller radius.
Other hot neptunes have very small cores, and low gravity at the top of the atmosphere means that the rate of atmosphere loss may be quite high, leading to the development of a gaseous tail.
Over time a hot neptune may evolve into a chthonian world, with minimal atmosphere.