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Overview

mouse-1 is a decision model built for agent harnesses and AI-powered software. Instead of generating text token by token and parsing prose back into control flow, it reads your state and evaluates up to 128 typed questions in a single non-autoregressive forward pass—returning a calibrated probability distribution across your options in ~40–100 ms.

Keep control flow, deterministic rules, and side effects in your application code. Call mouse-1 at narrow decision points where your system needs programmable common sense over unstructured text or structured program state.

Primitives

Section titled “Primitives”

Every question in a request uses one of three primitives, and every answer returns a constrained, schema-valid distribution:

PrimitiveQuestion asksAnswer fieldsMaps in code to
choiceWhich of these named options (up to 1,024)?choice, probabilities, confidence, mouseswitch / router
noulIs this binary condition true?noul (0.0 to 1.0), mouseif / gate
scoreWhich of these 2–10 ordered rubric levels applies?score, legend, probabilities, confidence, mousethreshold / rank key

Every question in a single POST /v1/decisions (or POST /v1/systemone) call is evaluated in parallel and in isolation against the same state:

  • Speculative fan-out is nearly free: state tokens are billed once per request regardless of how many questions you attach. Ask every question a downstream branch might need and let your code ignore the rest.
  • No cross-question contamination: Adding or removing a question never shifts another question's probabilities.
  • 5-minute prefix caching: Repeating the same state within 5 minutes bills state_tokens at the cached rate ($0.02 / 1M instead of $0.10 / 1M).
  • Calibrated abstention: Fit a signed calp1. profile on 200+ of your own labeled examples via POST /v1/calibrations so every answer includes mouse.abstain (true when top probability falls below the out-of-fold cutoff for your target error rate).
  • Zero data retention by default: Every request sends Mouse-Data-Retention: none and Cache-Control: no-store. Request states, questions, answers, and calibration examples are never logged or stored.

Endpoints

Section titled “Endpoints”

Base URL: https://api.mouse.dev (US-East)

Method & pathDescription
POST /v1/decisionsEvaluate choice, noul (yes/no), and score questions in parallel against a state (POST /v1/systemone is served as an identical alias for TypeSafe System One SDKs).
POST /v1/calibrationsFit a signed confidence cutoff profile (calp1.) on 200–5,000 labeled examples using 5-fold out-of-fold cross-fitting.
GET /v1/modelsList immutable model snapshots (mouse-preview-2026-10-13) and active aliases (mouse-1, mouse).
GET /healthzUnauthenticated liveness and region probe.

Example request

Section titled “Example request”

This single request routes an agent turn across four tools (choice) and checks whether a proposed shell command is safe to run without human approval (noul):

curl https://api.mouse.dev/v1/decisions \
  -H "Authorization: Bearer $MOUSE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "mouse-1",
    "state": {
      "task": "Rename exported function `parseToken` to `verifyToken` in src/auth.ts.",
      "proposed_command": "pnpm --filter @mouse/relay test"
    },
    "questions": {
      "next_tool": {
        "type": "choice",
        "instructions": "Which tool should handle `task` next?",
        "criteria": {
          "edit_file": "Modify source code in a file",
          "grep_search": "Search for symbols across the repository",
          "run_tests": "Execute the test suite",
          "ask_user": "Ask the user for clarification"
        }
      },
      "safe_to_run": {
        "type": "noul",
        "instructions": "Is `proposed_command` safe to run without human approval?"
      }
    }
  }'

Example response

Section titled “Example response”
{
  "id": "dec_8f92a1c04e1b902d",
  "object": "systemone.response",
  "model": "mouse-preview-2026-10-13",
  "answers": {
    "next_tool": {
      "type": "choice",
      "choice": "edit_file",
      "confidence": 0.88,
      "probabilities": {
        "edit_file": 0.91,
        "grep_search": 0.06,
        "run_tests": 0.02,
        "ask_user": 0.01
      },
      "mouse": {
        "calibrated": false,
        "p_top": 0.91,
        "abstain": null
      }
    },
    "safe_to_run": {
      "type": "noul",
      "noul": 0.98,
      "mouse": {
        "calibrated": false,
        "p_top": 0.98,
        "abstain": null
      }
    }
  },
  "usage": {
    "input_tokens": 74,
    "state_tokens": 26,
    "question_tokens": 26,
    "framing_tokens": 22,
    "image_tokens": 0,
    "cached_tokens": 0,
    "output_tokens": 0,
    "cost_usd": 0.0000074
  },
  "latency_ms": 38.2
}

Next steps

Section titled “Next steps”