This white paper introduces Siloed Visibility, a new governance concept within the AIVO Standard v3.5 framework.As large language models (LLMs) evolve into agentic ecosystems, user queries are increasingly routed through brand-owned agents that transact and retrieve data inside closed execution layers. This shift alters how visibility functions: discoverability through open generative recall is replaced by conditional access through invocation. AIVO Journal defines this condition as Siloed Visibility — the migration of brand presence from the model’s generative locus of authority into a private agentic environment. The paper outlines its implications for transparency, governance, and future measurement through dual Prompt-Space Occupancy metrics: PSOS-T (Text Visibility) and PSOS-A (Agentic Visibility). No empirical data are presented; this is a foundational definition paper establishing the terminology and scope for subsequent AIVO audits (2025–2026). The work contributes to AI governance by proposing visibility provenance as a new dimension of accountability under frameworks such as ISO/IEC 42001, the EU AI Act, and the OECD AI Principles.