System One is a typed decision API and TypeScript SDK that lets applications send a shared state plus named questions and receive structured Choice, Score, and Noul (yes/no probability) answers, with the app retaining control of actions.
Follow System One API to get an email when its listing changes, such as new pricing or features. One digest a day at most, and you can unsubscribe anytime.
- 01
Three decision primitives: Choice (up to 255 options), Score (2–10 ordered levels), and Noul (P(true) 0–1)
- 02
TypeScript SDK with typed choice(), score(), and booleanQuestion() helpers
- 03
Multiple hosted models (Jev, Clef Flash, Clef) with per-question, per-block credit pricing
- 04
Idempotency keys and refunds for failed inferences
- 05
Clairic extract() for structured field extraction
- 06
Coding-agent skill installable via npx skills for Cursor, Claude Code, and Codex
Freemium
The open-source TypeScript SDK (@system-one-ai/core, MIT-licensed, no runtime dependencies) is free to use without an account, but the hosted System One API runs on prepaid credits: 100 free credits on signup, then packs of 5,000 credits for $5.99, 20,000 for $19.99, and 120,000 for $99.99, with no recurring subscription.
Best for
Developers and agent builders who need fast, low-cost, typed classification, routing, or scoring decisions inside application code rather than free-text generation.
Not ideal for
Teams wanting a general-purpose chat or generative LLM, or those needing a mature, widely adopted ecosystem—the SDK is early-stage with only a few GitHub stars and hosted usage requires prepaid credits.
System One offers a clean, typed decision interface with a genuinely free MIT-licensed SDK and transparent credit pricing, well suited to routing and classification in agent workflows. However, it is a young project with a tiny community footprint, and the hosted API's value depends on whether its specialized decision models outperform simpler alternatives for your use case.
Core 0.8.0 (published 2026-10-21) added Clairic extract({ state, fields }); adapter-system-one 0.7.0 posts extract requests to /systemone with default model clairic. Jev released 2026-09-18 and Clef Flash 2026-10-01. Jev opened to all users on 2026-09-20 after its 2026-09-15 launch.
As of
Is System One API free?+
System One API is Freemium. The open-source TypeScript SDK (@system-one-ai/core, MIT-licensed, no runtime dependencies) is free to use without an account, but the hosted System One API runs on prepaid credits: 100 free credits on signup, then packs of 5,000 credits for $5.99, 20,000 for $19.99, and 120,000 for $99.99, with no recurring subscription. Check the official site for current plans.
Is System One API open source?+
System One API is not listed as open source on ai.dosa.dev - it is Freemium.
How much does System One API cost?+
The open-source TypeScript SDK (@system-one-ai/core, MIT-licensed, no runtime dependencies) is free to use without an account, but the hosted System One API runs on prepaid credits: 100 free credits on signup, then packs of 5,000 credits for $5.99, 20,000 for $19.99, and 120,000 for $99.99, with no recurring subscription. Pricing changes often - verify on the official site.
Who is System One API best for?+
Developers and agent builders who need fast, low-cost, typed classification, routing, or scoring decisions inside application code rather than free-text generation.
Who is System One API not ideal for?+
Teams wanting a general-purpose chat or generative LLM, or those needing a mature, widely adopted ecosystem—the SDK is early-stage with only a few GitHub stars and hosted usage requires prepaid credits.
What are the best System One API alternatives?+
The closest System One API alternatives on ai.dosa.dev are Pieces for Developers, agenttrace, Vibe Kanban - all listed under Developer Productivity & Workflow.
Who makes System One API?+
System One API is developed by Ziyu Li / System One. It is listed in the Developer Productivity & Workflow category on ai.dosa.dev.
Favorite this tool to revisit it later, or Zap it to contribute to the public vote count.