Latest Mobile Silk 45 user agents:

User Agent Platform Device
Mozilla/5.0 (Linux; Android 4.4.3; KFTHWI Build/KTU84M) AppleWebKit/537.36 (KHTML, like Gecko) Silk/45.1.99 like Chrome/45.0.2454.94 Safari/537.36 Fire OS 4 Kindle Fire HDX 7" WiFi
Mozilla/5.0 (Linux; Android 4.4.3; KFSOWI Build/KTU84M) AppleWebKit/537.36 (KHTML, like Gecko) Silk/45.1.99 like Chrome/45.0.2454.94 Safari/537.36 Fire OS 4 Kindle Fire HD 7" WiFi
Mozilla/5.0 (Linux; Android 4.4.3; KFASWI Build/KTU84M) AppleWebKit/537.36 (KHTML, like Gecko) Silk/45.1.99 like Chrome/45.0.2454.94 Safari/537.36 Fire OS 4 Fire HD 7
Mozilla/5.0 (Linux; Android 4.4.3; KFARWI Build/KTU84M) AppleWebKit/537.36 (KHTML, like Gecko) Silk/45.1.99 like Chrome/45.0.2454.94 Safari/537.36 Fire OS 4 Fire HD 6