As of June 2023, there are two operational cubesats in GEO.
AFRL Ascent and GS-1 incorporating payloads Nusantara H-1A and OrbitGuard-1.
Ascent was launched in 2021 and GS-1 launched in May 2023.
Ascent is a mission to demonstrate various CubeSat operations in geostationary orbit (GEO).
AFRL awarded a second contract for BCT to build, test and deliver a 12U-CubeSat bus for the Ascent mission. AFRL provided and integrated the Ascent payload with BCT’s 12U spacecraft bus.
Ascent’s mission has been to evaluate the performance of COTS technology, in the GEO space environment, where satellites match the Earth’s rotation.
Ascent completed its mission in October 2022.
The 55-pound (25-kilogram) Gravity Space GS-1 satellite separated from the Falcon Heavy. It's the first commercial CubeSat-based craft to fly in geostationary orbit.
GS-1 will secure orbital slot reservations and perform a rendezvous/docking experiment.
This is also providing hosting services for the payloads Nusantara H-1A, OrbitGuard-1.
(So in some cases it would look like 3 cubesats are in GEO orbit but it is just GS-1 with 2 additional but separate payloads)
So currently it looks like there are 2 cubesats in GEO.