Workers AI - Introducing Clef: Open-Source Decision Models

Meet @cf/cloudflare/clef and @cf/cloudflare/clef-flash, the first models trained by the Cloudflare Workers AI team, available on Workers AI today.

Clef is a decision model, in the same family as Typesafe's Jev ↗︎. Instead of generating text, it reads an input state and a set of typed questions, then returns a probability for every allowed answer. Your agent gets a structured decision it can act on immediately, for example: route the ticket, block the request, or escalate to a human. There is no free-form output to parse and no reasoning tokens to wait for.

Both models are hosted on Workers AI as Clef and Clef-flash. We are also open-sourcing the weights under the Apache 2.0 license on Hugging Face: Clef ↗︎ and Clef-flash ↗︎. Read the launch blog post ↗︎ for the full story, including how we trained them.

We are also launching a reinforcement learning (RL) fine-tuning service to help you tune Clef for your own workloads. Sign up to work with us as a design partner ↗︎.

Built for the hot path

Clef is designed to be fast so decisions come back in milliseconds. Across our 43 benchmark runs, we achieved speeds where Clef is 2.5x faster than Jev at the median, and Clef-flash 13x faster.

Latency	Clef	Clef-flash	Jev
Median	209.3 ms	38.8 ms	524.1 ms
p95	238.6 ms	122.4 ms	536.0 ms

Hosting on Workers AI adds to that speed. Requests run on GPUs across Cloudflare's network, running close to your users, so the network round trip stays short. You can put Clef directly in the request path of your agent, then hand off to an LLM on Workers AI to take action.

Leading the benchmarks

Across 10 decision benchmarks, a Clef model scores highest on 7, ahead of Jev and other open decision models. A few highlights:

Benchmark	Clef	Clef-flash	Jev
BFCL (case exact)	98.47	98.76	95.75
BANKING77 (macro-F1)	94.20	90.93	79.74
CLINC150+OOS (macro-F1)	97.43	66.77	89.27
Home appliances (case exact)	82.95	97.73	52.27

On Typesafe's own workflow evals, Clef beats Jev in 3 of 4 areas: invoice processing, customer service, and security incidents. The full results are on the Hugging Face model card ↗︎.

Drop-in compatible with Jev

Model	Size	Best for	Context window
@cf/cloudflare/clef	27B	Highest-precision decisions	64K tokens
@cf/cloudflare/clef-flash	9B	Latency-critical, hot-path decisions	64K tokens

Clef follows the System One API, so you can switch an existing Jev integration to Clef by changing the endpoint and model. Ask up to 64 questions per request, in three types:

• noul: A yes/no question. Returns the probability that the answer is yes.
• choice: Pick one option from a set you define. Returns the chosen option, a probability per option, and a confidence value.
• score: Rate against an ordered rubric. Returns a probability-weighted score and a probability per level.

const response = await env.AI.run("@cf/cloudflare/clef", {
	model: "clef",
	state: "Checkout has been failing for every customer for the last hour.",
	questions: {
		urgent: {
			type: "noul",
			instructions: "Is this support request urgent?",
		},
		team: {
			type: "choice",
			instructions: "Which team should handle this request?",
			criteria: {
				billing: "Payments, invoices, and refunds",
				technical: "Outages, errors, and configuration",
				sales: "Plans and upgrades",
			},
		},
	},
});

// response.answers.urgent.noul -> probability the request is urgent
// response.answers.team.choice -> highest-probability team

const response = await env.AI.run("@cf/cloudflare/clef", {
	model: "clef",
	state: "Checkout has been failing for every customer for the last hour.",
	questions: {
		urgent: {
			type: "noul",
			instructions: "Is this support request urgent?",
		},
		team: {
			type: "choice",
			instructions: "Which team should handle this request?",
			criteria: {
				billing: "Payments, invoices, and refunds",
				technical: "Outages, errors, and configuration",
				sales: "Plans and upgrades",
			},
		},
	},
});

// response.answers.urgent.noul -> probability the request is urgent
// response.answers.team.choice -> highest-probability team

What you can build with decision models

• Support triage: Decide whether a ticket is urgent and which team owns it, then route it without a human in the loop.
• Threat intelligence: Classify a website by category. Paired with Browser Run, Clef fetched, rendered, and classified a domain in 2.2 seconds, compared to 4.7 seconds for gpt-oss-120b in the same workflow.
• Trust and safety: Score user submissions against your own policy rubric and act on the probability.
• Agent guardrails: Let an agent check "should I take this action?" in tens of milliseconds before calling a tool.
• Visual classification: Pass up to four images alongside the state. Unlike text-only decision models, Clef has a vision encoder.

Get started

Use Clef through the Workers AI binding (env.AI.run()) or the REST API at /ai/run. You can also use AI Gateway with these endpoints.

For more information, refer to the Clef model page, the Clef-flash model page, and pricing.