Public AI Accountability: A Reference Standard for Third-Party Reliance AI accountability usually fails before any AI law is applied. When an AI system causes harm, disputes are not resolved by ethics statements, governance frameworks, audits, or explanations of how a system is meant to work. They are resolved by evidence. If responsibility cannot be fixed to a legal entity, if records of what happened do not exist, or if evidence cannot be produced after the fact, the dispute cannot be examined on its merits. This book defines the minimum publicly visible conditions that must already exist for AI accountability to be possible in practice. It is written for people who must make decisions without access, cooperation, or trust: regulators, litigators, courts, journalists, insurers, investors, and boards. It assumes no internal documentation, no privileged explanations, and no discretionary cooperation from system providers. The standard set out here treats accountability as a structural question, not a moral or technical one. Either the conditions needed to examine responsibility exist in public, or they do not. Where they do not, accountability is not weak or incomplete. It is structurally impossible for third-party reliance. The book establishes clear boundaries: what counts as public evidence - what does not - where accountability stops - and why it cannot be restored later by audits, explanations, or goodwill It identifies the foundational conditions that must exist for responsibility, evidence, reconstruction, and enforcement to function at all, and shows how accountability routinely collapses under ordinary legal rules long before AI-specific regulation becomes relevant. This is not an audit, a certification, or a compliance guide. It does not assess individual systems. It does not interpret law or give jurisdiction-specific advice. It is a reference standard for determining whether AI accountability can be relied upon by someone outside the organisation, using public evidence alone. If those conditions are not publicly established, accountability does not exist for that purpose.