Best answer: While you can control C by GE bulbs locally without a hub, you'll need a C-Reach to control them from out of Bluetooth range or use them with Amazon's Alexa voice assistant.
Amazon: ($41)
Operate your bulbs from afar with a C-Reach
C by GE makes relatively inexpensive smart bulbs that operate over Bluetooth, rather than Wi-Fi like bulbs from other brands like LIFX and Philips Hue. This helps keep the cost of each bulb down, but it means that you can't control them once you're out of their Bluetooth range — about 50 feet. If you have multiple bulbs, they can mesh together to extend range, but you still can't control them from afar unless you add a C-Reach smart bridge to the mix.
While not essential for using C by GE's C-Life and C-Sleep bulbs, the C-Reach improves the usability of each bulb by allowing them to work over Wi-Fi. This allows you to control your lights from anywhere through the , even when you're not home.
The C-Reach bridge also allows you to control your C by GE bulbs by voice through Google Assistant or Amazon Alexa (HomeKit support isn't available yet, but C by GE says it's coming soon). To use Alexa, you'll need to sign into your C by GE account in the Alexa app and add the "CbyGE" skill. For Google Assistant, just sign into your account within the Google Home app.
Remote control
C by GE C-Reach
Control your C by GE bulbs over Wi-Fi or through a voice assistant.
C by GE bulbs work fine over Bluetooth without a hub, but the C-Reach allows you to control them even when you're away from home. You also gain access to voice controls through either Alexa or Google Assistant.