List all variable fonts from Google Fonts API?

I need to get a list of all variable fonts available through the Google Fonts API.

I can get all the font names from this endpoint. There are some parameters you can add but I don't think that a variable font filter is among them: https://www.googleapis.com/webfonts/v1/webfonts?key=API_KEY&sort=popularity

I don't think I can filter the results after making the API call. Here "Open Sans" is a variable font but I don't see anything to indicate this in the response.

{
      "family": "Open Sans",
      "variants": [
        "300",
        "regular",
        "500",
        "600",
        "700",
        "800",
        "300italic",
        "italic",
        "500italic",
        "600italic",
        "700italic",
        "800italic"
      ],
      "subsets": [
        "cyrillic",
        "cyrillic-ext",
        "greek",
        "greek-ext",
        "hebrew",
        "latin",
        "latin-ext",
        "vietnamese"
      ],
      "version": "v34",
      "lastModified": "2022-09-22",
      "files": {
        "300": "http://fonts.gstatic.com/s/opensans/v34/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsiH0C4nY1M2xLER.ttf",
        "regular": "http://fonts.gstatic.com/s/opensans/v34/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsjZ0C4nY1M2xLER.ttf",
        "500": "http://fonts.gstatic.com/s/opensans/v34/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsjr0C4nY1M2xLER.ttf",
        "600": "http://fonts.gstatic.com/s/opensans/v34/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsgH1y4nY1M2xLER.ttf",
        "700": "http://fonts.gstatic.com/s/opensans/v34/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgsg-1y4nY1M2xLER.ttf",
        "800": "http://fonts.gstatic.com/s/opensans/v34/memSYaGs126MiZpBA-UvWbX2vVnXBbObj2OVZyOOSr4dVJWUgshZ1y4nY1M2xLER.ttf",
        "300italic": "http://fonts.gstatic.com/s/opensans/v34/memQYaGs126MiZpBA-UFUIcVXSCEkx2cmqvXlWq8tWZ0Pw86hd0Rk5hkaVcUwaERZjA.ttf",
        "italic": "http://fonts.gstatic.com/s/opensans/v34/memQYaGs126MiZpBA-UFUIcVXSCEkx2cmqvXlWq8tWZ0Pw86hd0Rk8ZkaVcUwaERZjA.ttf",
        "500italic": "http://fonts.gstatic.com/s/opensans/v34/memQYaGs126MiZpBA-UFUIcVXSCEkx2cmqvXlWq8tWZ0Pw86hd0Rk_RkaVcUwaERZjA.ttf",
        "600italic": "http://fonts.gstatic.com/s/opensans/v34/memQYaGs126MiZpBA-UFUIcVXSCEkx2cmqvXlWq8tWZ0Pw86hd0RkxhjaVcUwaERZjA.ttf",
        "700italic": "http://fonts.gstatic.com/s/opensans/v34/memQYaGs126MiZpBA-UFUIcVXSCEkx2cmqvXlWq8tWZ0Pw86hd0RkyFjaVcUwaERZjA.ttf",
        "800italic": "http://fonts.gstatic.com/s/opensans/v34/memQYaGs126MiZpBA-UFUIcVXSCEkx2cmqvXlWq8tWZ0Pw86hd0Rk0ZjaVcUwaERZjA.ttf"
      },
      "category": "sans-serif",
      "kind": "webfonts#webfont"
    },

There is this site which lists all variable fonts. In the developer console (F12) I saw it downloading this file:

https://fonts.google.com/metadata/fonts

This file contains all fonts. If the "axes" array of a font is not empty then it's definitely a variable font. Maybe you have to check other property names (I am not that familiar with variable fonts).