This was found in south Texas, USA. It size was around 3 centimetres without considering the antennas or legs.
The green, narrow body suggests this is indeed a katydid.
The red antennae, red eyes, and small, red-lined wings looks like the green form of a Paracyrtophyllus robustus (Central Texas leaf katydid) nymph.
Credit: Mike Quinn ; Source: Bugguide.net
Source: Austin Bug Collection