As communications service providers (CSPs) advance toward Autonomous Network Level 4 (AN L4), trust in AI-driven operations has become a critical barrier to deployment. While many CSPs have adopted Autonomous Networks as a core transformation strategy, concerns around AI hallucination, data integrity, and operational security continue to slow progress—particularly for high-impact, self-managing network functions. The Building Trust in AN L4 Catalyst directly addresses this challenge by establishing a trusted AI foundation that CSPs can rely on for secure, autonomous network operations. The Catalyst focuses on reducing AI hallucination risk and strengthening confidence in AI decision-making, enabling CSPs to safely unlock self-X capabilities that improve operational efficiency, enhance customer experience, and support new revenue opportunities. The solution introduces a two-pronged innovation approach. First, it develops a domain-specific large language model grounded in CSP knowledge management systems and trained on historical network operations patterns, ensuring AI reasoning is context-aware and aligned with real operational behavior. Second, it strengthens data governance using TM Forum assets and best practices, improving data quality, integrity, and lifecycle management to support sustainable and trustworthy AI operations. Aligned with TM Forum Autonomous Networks and Open Digital Architecture principles, the Catalyst demonstrates how trust, security, and explainability can be embedded into AN L4 from the outset. Success is measured through AI performance indicators such as accuracy and error rates, providing clear, quantifiable evidence of improved reliability. By building confidence in AI-driven decision-making, the Catalyst accelerates AN L4 adoption, enables agile operating models, and lays the foundation for CSPs to expose autonomous capabilities as trusted services—turning trust in AI into a strategic advantage.