This is what I get for pushing to master

src/Discord.Net/Net/WebSockets/GatewaySocket.cs

@@ -43,7 +43,7 @@ namespace Discord.Net.WebSockets
             //Token = rest.Token;
 
             var gatewayResponse = await rest.Send(new GatewayRequest()).ConfigureAwait(false);
-            string url = $"{gatewayResponse.Url}?encoding=json&v=4";
+            string url = $"{gatewayResponse.Url}/?encoding=json&v=4";
             Logger.Verbose($"Login successful, gateway: {url}");
 
             Host = url;