March 28 (Reuters) - Elon Musk's artificial intelligence startup xAI said on Thursday it will launch an improved version of its chatbot Grok called Grok-1.5, which will be available to early testers and existing Grok users on social media platform X in the coming days. (Reporting by Rishabh Jaiswal in Bengaluru; Editing by Subhranshu Sahu)