LunaBill builds AI voice agents that automate insurance claim follow-up calls for healthcare billing teams. The platform handles claim status inquiries, accounts-receivable recovery, appeals follow-ups, and reprocessing calls, integrating with existing billing software and running up to 100 concurrent agents per client. Fine-tuned on over 1.2M call transcripts, the system had completed 60,000+ automated calls and reported $764K contracted ARR at launch. LunaBill is part of Y Combinator's Fall 2025 batch.