I’m going to try to keep this simple, so bear with me. The facts are really complicated. 
The TL;DR FAQ:
“Cync /C By GE” devices don’t work with SmartThings, whether you have a hub or not.
Most “Enbrighten” and older “GE“ Z wave or Zigbee devices made by Jasco do work with SmartThings, but they do require a smartthings/Aeotec hub, and may need custom code for advanced features.
The “GE” logo in the SmartThings app is for the Jasco devices.
GE smart appliances don’t work directly with smartthings, but unlike Cync, they do have a pretty good IFTTT service so you can get some integration that way.
https://products.geappliances.com/appliance/gea-support-search-content?contentId=23807
The rest of this post provides more details for those interested.
HISTORY
Several years ago GE licensed its name to Jasco for smart light switches and smart plugs. These were zwave, zigbee, and eventually some Bluetooth. Most of these required a hub, and most worked well with SmartThings. (but not the Bluetooth versions.)
If you select the “GE“ brand in the smartthings app these are the devices you can choose from.
They eventually added the “Enbrighten” name but kept the GE logo.
In 2019 GE introduced its own brand of Bluetooth and Wi-Fi smart home devices under the “C by GE“ brand. These do not require a hub, but they don’t work with SmartThings either. 
In 2020, Jasco started selling the same old “GE“ zwave and Zigbee devices under the new “Enbrighten” name without the GE logo on the box. These continue to require a hub and continue to work well with smartthings. You can find them in the smartthings app under the Enbrighten name.
And then in 2021, GE announced that the “C by GE“ brand was being renamed to “Cync.” Still doesn’t require a hub, still doesn’t work with smartthings. There are some hints that it may eventually work with HomeKit and/or Matter, but that hasn’t been released yet. If they do ever get to matter compliance then they might work with SmartThings but as of this writing, July 2021, they do not.
Current Situation as of July 2021
Enbrighten zwave and Zigbee devices require a hub and will mostly work with smartthings, although some advanced features of some models might require custom code. Older GE Zwave and zigbee devices (manufactured by Jasco) are in the same situation: they require a hub and will mostly work with SmartThings, although some features of some models may require custom code.
Cync devices do not require a hub and do not work with SmartThings. The same is true for the older “C by GE“ models. You might be able to get some partial integration through Alexa routines, but it won’t be very satisfying.
Note that unlike other major smart lighting brands, including Hue, Lutron, Ikea, Legrand, and Schneider, GE has not joined the Matter (formerly Project CHIP) project, so no telling if there will be eventual compatibility that way or not.
For now, Cync from GE lighting doesn’t work with SmartThings.
Enbrighten from Jasco, including the older products that have the GE logo on the box, mostly does, although custom code may be required for some advanced features.
@Automated_House @jkp @HalD @nathancu
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