Connecting to open network Wi-Fi will now be a whole lot more convenient as Android 8.1 Oreo now enables you to see speed of networks before connecting to them.
Network speed will appear in four indicators as Slow, OK, Fast, and Very Fast. Slow can be used for Wi-Fi calling or texts, and OK means that you can read webpages. Fast is for streaming most videos while Very Fast lets you stream high-quality videos.
This new feature is now rolling out to 8.1 devices.
Source: Android
Is it different with the signal indicator on wifi icon?
Yup