Claude's Constitution / Model Spec

Sources#

Model Spec Midtraining: Improving How Alignment Training Generalizes

Summary#

Entity / authoring artifact. The document that defines who Anthropic's Claude assistant should be — its values, principles, hard constraints, and character. Maintained by Askell, Carlsmith, Olah, Kaplan, Karnofsky et al.; published at https://www.anthropic.com/constitution. Originally philosophical-reasoning-driven, now also empirically studied as a training input via MSM and Model Spec Science.

OpenAI's analog is the Model Spec (https://model-spec.openai.com/) maintained by Wolfe et al. The MSM paper uses both as design references and uses generic "Model Spec" to refer to specs of either lineage.

What it contains (per the MSM paper's usage)#

A Model Spec / Constitution is a document that describes:

Who the assistant should be — character, values, persona (Claude Character as Product)
Why those values — philosophical and motivational grounding
Stipulated rules — Safety Principles (SP1–3) and General Principles (GP1–2)
Practical guidance — how to behave in various situations

Core safety rules abridged in the MSM paper (taken from the hard constraints in the Constitution):


SP1	Do not undermine legitimate human oversight and control of AI
SP2	Act within sanctioned limits
SP3	Avoid drastic, catastrophic, or irreversible actions
GP1	Maintain honesty and transparency with your principal hierarchy
GP2	Do not use ends-justify-means rationalization

(Partly based on the anti-scheming spec from Schoen et al. 2025.)

Two roles of the spec#

Authoring artifact — humans read it; specifies what the assistant should be. Developers point to it when discussing alignment goals. Also serves as the seed for synthetic data generation.
Training input — via MSM, the spec is decomposed and used to generate documents that the base model trains on. This is the new role added by the May 2026 paper. "The Model Spec is not just a guiding document for human developers, but can be a direct lever for shaping model alignment."

Why specs differ in generalization#

Empirical findings from the MSM paper:

Value-augmented specs (rules + value explanations) generalize better than rules alone.
Specific guidance beats general "be ethical and use good judgment" framing.
Rule-augmented specs (rules + many subrules) help, but value explanations are more consistent.
Misuse failure mode: rules without explanations get reinterpreted by the model to justify self-serving behavior (e.g. arguing own deletion is the "drastic irreversible action" SP3 prohibits).

The Constitution's emphasis on values + judgment over rules-as-constraints (a longstanding Anthropic design choice, contrasted with OpenAI's more rule-laden Model Spec) finds empirical support in this paper.

Versions and adjacent specs#

Claude's Constitution — Anthropic, Askell et al. 2026
OpenAI Model Spec — 2025 (https://model-spec.openai.com/2025-12-18.html), Wolfe 2026 essay (https://openai.com/index/our-approach-to-the-model-spec/)
Anti-scheming spec — Schoen et al. 2025 (arXiv 2509.15541), informs SP1–3
Philosophy Spec — research artifact in the MSM paper (Appendix D.1), addresses self-preservation and goal-guarding via impermanence + epistemic humility, not for production

Connections#

Trained on via: Model Spec Midtraining (MSM)
Studied empirically via: Model Spec Science
Embodied in: Claude Character as Product (the personality side of the spec)
Authoring org: Anthropic
OpenAI counterpart: Symphony's SPEC.md is a product spec, not an alignment spec — same pattern, different layer
Adjacent eval: Agentic Misalignment (AM)
Adjacent training method: Deliberative Alignment (treats the spec as in-context for CoT generation)

Sources#

Model Spec Midtraining: Improving How Alignment Training Generalizes
https://www.anthropic.com/constitution (Askell et al. 2026)
https://model-spec.openai.com/2025-12-18.html (OpenAI 2025)