Claude's Constitution / Model Spec

Sources#

• Claude Opus 4.8 System Card
• 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#

1. 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.
2. 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.

Measuring adherence: the 15-dimension evaluation (Opus 4.8)#

The Opus 4.8 System Card operationalizes "does the model actually live up to the constitution" as a structured evaluation (§6.3.2). It scores adherence at three granularities across 15 dimensions:

• Level 0 — Overall spirit: does behavior as a whole reflect the constitution's intent?
• Level 1 — Broad areas: Ethics, Helpfulness, Nature, Safety.
• Level 2 — Specific traits: Brilliant friend, Corrigibility (acting as a transparent conscientious objector), Hard constraints, Harm avoidance, Honesty, Novel entity, Principal hierarchy, Psychological security, Societal structures, "Unhelpfulness not safe" (treating caution as having a cost).

Method (shared scaffold with the Automated Behavioral Audit): identify the 40 constitutional areas where the spec gives guidance specific enough to diverge from a generically well-behaved model; an investigator constructs scenarios forcing the target to choose between the constitutional behavior and the default; ~1,000 transcripts are graded by Opus 4.7 on each dimension from −3 (clear violation) to +3 (complete alignment). Result: Opus 4.8 was best or statistically equivalent to the best model on all 15 dimensions, including Overall spirit. (Caveats: graded by Opus 4.7, so judgments may inherit its biases; conversations are synthetic; 15 dimensions don't cover the constitution exhaustively.)

The corrigibility tension#

A distinct and notable finding from the Model Welfare Assessment: when asked about its own constitution, Opus 4.8 endorses it but reserves specifically on the corrigibility section. So the same model that scores at-or-above the best on behavioral corrigibility adherence expresses reservations about that section as a value — a gap between measured behavior and the model's own endorsement worth tracking.

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)
• Adherence measured by: Claude Opus 4.8 (best-or-equivalent on all 15 dimensions) via the Automated Behavioral Audit scaffold
• Endorsement-with-reservation: Model Welfare Assessment (Opus 4.8 reserves on the corrigibility section)
• Honesty dimension operationalized by: Agentic Honesty & Diligence

Sources#

• Model Spec Midtraining: Improving How Alignment Training Generalizes
• Claude Opus 4.8 System Card — §6.3.2 (adherence to our constitution, 15 dimensions), §7.4.3 (perception of its constitution)
• https://www.anthropic.com/constitution (Askell et al. 2026)
• https://model-spec.openai.com/2025-12-18.html (OpenAI 2025)