Jev API

What is the Jev API?

Jev is a frontier System One model from TypeSafe AI, announced September 15, 2026. Built by Diogo Almeida (co-inventor of RLHF and InstructGPT at OpenAI), backed by $40M led by DCVC.

Unlike LLMs that generate text token-by-token, Jev evaluates your program state against a map of typed questions and returns structured answers — one per question — in a single parallel pass. That means:

Source: TypeSafe AI & independent benchmarks. Jev is available in early access — you need a waitlisted API key. You can also access it through OpenRouter, Vercel AI Gateway, Netlify AI Gateway, and AIMLAPI.

The endpoint

One endpoint. Three question types. That's the entire API surface.

# Install: pip install typesafe-sdk
from typesafe_sdk import Choice, Noul, Score, TypeSafeClient

client = TypeSafeClient()

response = client.system_one(
    state="I was charged twice for order A-104. Please refund.",
    questions={
        "department": Choice(
            instructions="Which team should handle this?",
            criteria={
                "billing": "Payment or subscription issues",
                "technical": "Bugs or integration problems",
                "sales": "Pricing or account questions",
            },
        ),
        "frustration": Score(
            instructions="How frustrated is the customer?",
            criteria=["Calm", "Frustrated", "Very angry"],
        ),
        "refund_wanted": Noul(
            instructions="The customer explicitly asks for a refund",
        ),
    },
)

print(response.answers["department"].choice)       # "billing"
print(response.answers["department"].confidence)    # 0.85
print(response.answers["frustration"].score)         # 1.6
print(response.answers["refund_wanted"].noul)          # 0.92

// Install: npm install @typesafe-ai/sdk
import { choice, noul, TypeSafeClient } from "@typesafe-ai/sdk";

const client = new TypeSafeClient();

const response = await client.systemOne({
    state: "I was charged twice. Please fix this ASAP.",
    questions: {
        category: choice("What is this about?", {
            billing: "Payment or subscription issues",
            technical: "Bugs or integration problems",
            other: "Anything else",
        }),
        urgent: noul("The message conveys urgency"),
    },
});

console.log(response.answers.category.choice); // "billing"
console.log(response.answers.urgent.noul);    // 0.88

The three primitives

The entire API is three question types. That's not a limitation — it's the design.

Patterns that change your architecture

Confidence-gated routing

Jev is trained with RLCD (Reinforcement Learning for Calibrated Decisions), so confidence is meaningful in aggregate: higher confidence = higher accuracy. Set different thresholds per action based on what being wrong costs.

action = response.answers["intent"]

if action.confidence < 0.5:
    route_to_human(user_message)   # genuinely unsure
elif action.choice == "check_balance":
    show_balance(account_id)        # read-only, low bar
elif action.choice == "approve_transfer":
    if action.confidence > 0.85:   # moves money, high bar
        approve_transfer(account_id)
    else:
        ask_user_to_confirm("Approve this transfer?")

Speculative fan-out

Questions are evaluated in parallel — a tenth question costs tokens but almost zero extra time. Ask everything up front and let code decide what mattered. TypeSafe's cookbook: 13-question batching is 12.2× cheaper and 10.0× faster than asking one at a time, with identical answers.

SDKs & integrations

How to get an API key

Jev is in early access. Join the waitlist at console.typesafe.ai/settings/keys. Once approved, export your key:

export TYPESAFE_API_KEY="sk-..."

No TypeSafe key yet? You can also access Jev through OpenRouter, Vercel AI Gateway, Netlify AI Gateway, or AIMLAPI — all listed above.

More resources

Official API reference — full HTTP spec, request/response shapes, error codes, rate limits.

TypeSafe Documentation — concepts, foundations, patterns, demos, cookbooks.

Introducing System One Models & Jev — the official launch post.

We also cover deeper topics on dedicated pages: Jev API Key guide, Jev Docs, Jev Model, System One explained, Jev vs Claude.