Build domain-specific long-horizon agents

Open source · Python · Apache 2.0

Build domain-specific
long-horizon agents.

Cayu is an open-source Python framework for building and running domain-specific long-horizon agents. Compose a harness around your tools, knowledge, and business rules—with a durable runtime built in.

pip install cayu

How Cayu works

Build the agent.
Shape how it works.

Cayu brings the building blocks, harness components, and runtime together in one Python framework. You supply the domain knowledge and define how the agent does its job.

Framework, harness, runtime, and agent: their roles in Cayu
Concept	Its role in Cayu
Framework	The Python structure, APIs, defaults, and components you build with.
Harness	The system you assemble with Cayu: context, tools, memory, policies, domain logic, and verification.
Runtime	The integrated execution machinery: sessions, state, workers, recovery, approvals, and budgets.
Agent	The resulting product that performs work in your domain.

An agent built with CayuA product that performs work in your domain

Cayu frameworkPython APIs, defaults, and components to build with

Your domain-specific harnessAssembled and customized with Cayu

Context
Tools
Policies
Domain logic
Memory
Verification & evals

01
Model
Propose the next step
Your choice of provider
02
Tools
Check permission, then act
Your systems and functions
03
Result
Collect and verify evidence
Context for what comes next

Continue toward the goal Wait for input Finish

Cayu runtimeIntegrated execution, built in

Durable sessions & stateWorkers & recoveryApprovals & budgetsReplay & observability

Build with the framework. Assemble your harness. Run on the integrated runtime. The result is your agent.

Why build with Cayu?

Long-horizon work

A clear goal.
Hours of work to get there.

“Process these 5,000 documents” has a finish line. Getting there may involve thousands of calls, new evidence, a human decision, and a restart.

Hour 3

One goal. Thousands of decisions.

Review 5,000 documents, extract the required fields, and flag exceptions. Your harness defines the checks. Cayu records the execution.

The goal stays bounded as the execution grows.

Document review / Session 052Running

Documents reviewed1,240 / 5,000

Estimated model cost$18.60 / $100 budget

Document batch completed

Results and session progress recorded

Continue reviewing the remaining documents.

This example shows the lifecycle you can build with Cayu. Your harness defines the business rules and completion checks.

Start building

Python you can
make your own.

Start with a project that has a place for your prompts, tools, policies, memory, and evals. Bring the libraries and domain code your team already uses.

Read the quickstart

Python 3.11+ · Run locally or on your infrastructure

Terminal

01 / Create your project

pip install cayu
cayu new support-agent
cd support-agent

02 / Check and evaluate

cayu check --fail-on warning --json
pytest
cayu eval run

03 / Run your agent

Configure your model provider in configuration/settings.py or CAYU_PROVIDER first.

python run.py --message "Review this change."

Build with Codex, Claude Code, or Cursor

Open the generated project in your development tool, or start with this prompt and build and refine your agent together.

Install cayu and create a document review agent. Use cayu new to scaffold the project. Define the required fields, flag exceptions for human review, and add completion checks and evals. Ask me about the document format and model provider before configuring them.

What Cayu handles

The foundation behind the work.

Keep work moving.

Maintain state across long sessions. Coordinate workers, pause for input, and recover from recorded evidence.

Sessions & recovery

Keep actions under control.

Define which tools an agent may use, when approval is required, and how much a run may spend.

Permissions & budgets

Understand and improve.

Inspect the work, trace model costs, and evaluate behavior using the path the agent took and the result it produced.

Observability & evals

Explore the framework

Build, then operate

Your agent.
Your way to run it.

Build your agent and its domain-specific harness with Cayu. Run it on your own infrastructure, or use Cloud as your team’s shared workspace.

Cayu · Open source

Run on your infrastructure.

Compose your harness in Python. Choose your models, stores, and execution environment. Inspect sessions, usage, and evals in the included runtime dashboard.

Explore deployment options Open source · Cayu Cloud is optional

Cayu Cloud

Operate together in Cloud.

Build in Console, deploy your agents, and manage their work in a shared workspace. Connect systems, set policies, and evaluate improvements with Compound.

Explore Cayu Cloud For teams managing the agent lifecycle

Why we built it

Built from the work.

We kept rebuilding the same infrastructure around agents for finance, accounting, and enterprise operations. The complexity grew when the work had to continue across days, decisions, and failures.

We brought those building blocks and the runtime together in Cayu. Our background in ML and industrial systems shapes the approach: domain knowledge, verification, and the system around the model matter.

Meet Cayu

A few useful answers

What is Cayu?

Cayu is an open-source Python framework for building and running domain-specific long-horizon agents. It provides components and defaults to assemble your agent’s harness, with an integrated runtime for durable, controlled execution.

What is an agent harness?

A harness is the system around the model: context, tools, policies, domain logic, memory, and verification. You assemble and customize it with Cayu to define how your agent does its job.

When does Cayu become useful?

When work spans many decisions, interacts with real systems, waits for people, needs to survive interruptions, or operates under cost and permission constraints. The goal can be bounded even when execution takes hours or days.

Can I choose the model and control the loop?

Yes. Cayu provides defaults and replaceable Python contracts for models, context, tools, execution, and storage. Supported provider integrations include OpenAI, Anthropic, Amazon Bedrock, Google Vertex AI, and OpenAI-compatible APIs. You can implement your own provider contract.

Do I need Cayu Cloud?

No. Agents built with Cayu run on infrastructure you choose, with a packaged operator dashboard included. Cayu Cloud is an optional shared workspace for building, deploying, operating, and improving your agents.

Is Cayu open source?

Yes. Cayu is licensed under Apache 2.0. You can inspect, modify, and self-host it. We use Cayu in enterprise deployments; the open-source project is early, and we welcome feedback from teams building domain-specific long-horizon agents.

Build for the long run

Bring your domain.
Build your agent.

What does your agent need to do?
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