Android get IP-Address of a hotspot providing device

I tested a small couple of different devices and it seems that the hotspot providing device has always the IP 192.168.43.1 on its network. Can somebody please check/confirm this assumption?

You're almost right, the default IP address of hotspot is 192.168.43.1 (If device maker didn't change.)

You can check the source code of Android framework (AOSP).

/frameworks/base/services/java/com/android/server/connectivity/Tethering.java /frameworks/base/wifi/java/android/net/wifi/WifiStateMachine.java

In the Tethering.java,

private static final String USB_NEAR_IFACE_ADDR      = "192.168.42.129";
private static final int USB_PREFIX_LENGTH        = 24;

// USB is  192.168.42.1 and 255.255.255.0
// Wifi is 192.168.43.1 and 255.255.255.0
// BT is limited to max default of 5 connections. 192.168.44.1 to 192.168.48.1
// with 255.255.255.0

private String[] mDhcpRange;
private static final String[] DHCP_DEFAULT_RANGE = {
    "192.168.42.2", "192.168.42.254", "192.168.43.2", "192.168.43.254",
    "192.168.44.2", "192.168.44.254", "192.168.45.2", "192.168.45.254",
    "192.168.46.2", "192.168.46.254", "192.168.47.2", "192.168.47.254",
    "192.168.48.2", "192.168.48.254",
};

Also, in the WifiStateMachine.java

private boolean startTethering(ArrayList<String> available) {                                 

    boolean wifiAvailable = false;                                                            

    checkAndSetConnectivityInstance();                                                        

    String[] wifiRegexs = mCm.getTetherableWifiRegexs();                                      

    for (String intf : available) {                                                           
        for (String regex : wifiRegexs) {                                                     
            if (intf.matches(regex)) {                                                        

                InterfaceConfiguration ifcg = null;                                           
                try {                                                                         
                    ifcg = mNwService.getInterfaceConfig(intf);                               
                    if (ifcg != null) {                                                       
                        /* IP/netmask: 192.168.43.1/255.255.255.0 */                          
                        ifcg.setLinkAddress(new LinkAddress(                                  
                                NetworkUtils.numericToInetAddress("192.168.43.1"), 24));      
                        ifcg.setInterfaceUp();                                                

                        mNwService.setInterfaceConfig(intf, ifcg);                            
                    }                                                                         
                } catch (Exception e) {                                                       
                    loge("Error configuring interface " + intf + ", :" + e);                  
                    return false;                                                             
                }                                                                             

                if(mCm.tether(intf) != ConnectivityManager.TETHER_ERROR_NO_ERROR) {           
                    loge("Error tethering on " + intf);                                       
                    return false;                                                             
                }                                                                             
                mTetherInterfaceName = intf;                                                  
                return true;                                                                  
            }                                                                                 
        }                                                                                     
    }                                                                                         
    // We found no interfaces to tether                                                       
    return false;                                                                             
}   

Therefore, the default value is 192.168.43.1 .