What Is Constitutional AI? How Anthropic Trains Claude to Behave

The Core Idea

Constitutional AI is a training technique developed by Anthropic to shape how its Claude models behave, used as part of the broader process of fine-tuning the model after its initial training on text data. Rather than depending entirely on human reviewers to judge each individual response as good or bad, constitutional AI gives the model a written set of guiding principles — a "constitution" — and trains it to evaluate and revise its own outputs against those principles.

Why Anthropic Built It

Traditional alignment techniques for large language models rely heavily on a method called reinforcement learning from human feedback, in which human raters compare pairs of model outputs and indicate which one they prefer. This approach works, but it has limits: it requires enormous amounts of human labor, the resulting judgments can be inconsistent between different raters, and it can be difficult for outside observers to know exactly what values are being reinforced. Anthropic designed constitutional AI partly to address these limitations by making the underlying principles explicit and auditable rather than implicit in a large set of individual human judgments.

How the Process Works

In broad terms, constitutional AI training happens in two main stages. In the first stage, the model is prompted to generate a response, then critique that response against the stated principles, and then revise it to better align with those principles — essentially teaching itself through self-critique using the constitution as a reference. In the second stage, a related technique uses AI-generated feedback, informed by the same constitutional principles, to further reinforce preferred behavior, reducing how much the system depends on large volumes of human-labeled data.

What's In the Constitution

The specific principles Anthropic has used in Claude's constitution draw from multiple sources, including ideas about avoiding harmful, deceptive, or discriminatory outputs, respecting user autonomy, and drawing on language from documents like the United Nations Declaration of Human Rights as a starting reference point for universal values. The exact wording and structure of Claude's constitution has evolved across model generations as Anthropic's own thinking about AI behavior and safety has developed.

Benefits and Limitations

Proponents of constitutional AI argue that it makes a model's values more transparent, since the constitution itself can be published and scrutinized, and more scalable, since it reduces reliance on enormous volumes of human labeling. Critics and researchers studying the approach have noted that writing a constitution that anticipates every difficult real-world scenario is inherently challenging, and that, like any alignment technique, constitutional AI cannot fully guarantee a model will behave exactly as intended in every situation it encounters after deployment.

Why It Matters Beyond Anthropic

Constitutional AI has become one of the more widely discussed alignment techniques in the AI research community, influencing how other labs think about combining explicit, written value statements with automated feedback loops. As AI models take on more autonomous, agentic tasks with less direct human oversight, techniques like constitutional AI are likely to remain central to ongoing efforts to keep increasingly capable systems predictable and aligned with human intentions.