AI governance has shifted from steering committees and slide decks to integrated control planes that inventory every model and agent, classify risk against EU AI Act and NIST AI RMF, run continuous bias and safety evaluation, enforce deployment gates, and generate audit-ready evidence. This guide covers the leading platforms (Credo AI, Fairly AI, Holistic AI, IBM watsonx.governance, Microsoft Purview AI Hub, OneTrust AI Governance, hyperscaler-native), the reference architecture for an internal AI governance plane, the build-versus-buy decision, and what good looks like 12 months in.