# Cayu > Cayu is an open-source Python framework for building and running domain-specific long-horizon agents, with a durable runtime built in. Framework: Cayu's Python APIs, components, and defaults for building and running agents: models, tools and integrations, context, knowledge, memory, web/browser capabilities, multi-agent coordination, workspaces, verification, and evals. Harness: the system developers assemble with Cayu, including context, tools, memory, policies, domain logic, verification, and evals. Runtime: the framework’s integrated execution machinery for durable sessions and state, task dispatch, workers, recovery, approvals, budgets, replay, and recorded execution evidence. Agent: the resulting product that performs work in a particular domain. Cloud: optional deployment and shared operation of agents built with the framework. Developers build and customize the domain-specific harness with Cayu. The runtime is reusable across domains. Claude Code, Codex, and Cursor can help developers write a Cayu project; they are development tools, not harnesses to import. A bounded goal may require hours or days of execution. Cayu supports recorded progress across interruptions, human input, and recovery. Ambiguous external effects require reconciliation; durable state does not establish an unknown result. ## Pages - [Homepage](https://cayu.dev/): What Cayu is, how it fits, a sample long-running job, and a quickstart. - [Framework](https://cayu.dev/framework/): Agent-building capabilities, harness composition, the integrated runtime, evaluations, deployment, Python contracts, and cost evidence. - [End-to-end walkthrough](https://cayu.dev/walkthrough/): A campus dining agent built in 14 steps, from Python building blocks and harness composition to durable sessions, approval, and verification. - [Why Cayu?](https://cayu.dev/why-cayu/): Why domain-specific long-horizon agents benefit from an integrated Python framework. - [Comparison](https://cayu.dev/comparison/): Framework capabilities compared through a versioned public code-audit snapshot, including execution and recovery boundaries. - [Quickstart](https://cayu.dev/docs/get-started/quickstart/): Installation, project generation, tests, evaluations, and model configuration. - [Documentation](https://cayu.dev/docs/): Guides, runtime and operational references, and the Python, HTTP and CLI API reference. - [Examples](https://github.com/cayu-dev/cayu/tree/main/examples): Executable examples. ## Framework, application, and Cloud Cayu is Apache-2.0 and runs independently of Cayu Cloud on application-selected infrastructure. Applications own their customer interfaces, authentication, business authorization, domain logic, and completion criteria. The framework includes a packaged operator dashboard for sessions, workflows, usage, and evals. Configure durable storage, access policy, model providers, and execution boundaries for the deployment. Native Python tools are trusted application code. Cayu Cloud is an optional shared workspace for building, deploying, operating, and improving agents built with Cayu. It is currently invite-only. Console is the building and editing experience. Compound focuses on evaluations and reviewed improvement. Its planned Self Improvement — Genetic Algorithm experience is marked Coming. Cayu supports multiple provider integrations and replaceable Python contracts. This is separate from Cloud's model-access and billing experience. Cayu's paired cost comparisons measure a context, caching, or tool-exposure strategy on a given workload and price source. Their results are workload-specific, not universal token or whole-workflow savings. - [Cayu for the enterprise](https://cayu.ai/) - [Cayu Cloud](https://cloud.cayu.dev/) - [Source](https://github.com/cayu-dev/cayu) - [Runtime contracts](https://github.com/cayu-dev/cayu/blob/main/docs/runtime-contracts.md) - [Cost optimization guide](https://github.com/cayu-dev/cayu/blob/main/docs/cost-optimization.md) - [Community](https://discord.gg/VUNHpjTDQ) ## Developer documentation ### Start here - [Docs](https://cayu.dev/docs/): choose a reading path. - [Quickstart](https://cayu.dev/docs/get-started/quickstart/): cayu new, inspect, strict check, tests, eval and first live run. - [Coding agents](https://cayu.dev/docs/get-started/coding-agents/): project seams, instructions and behavioral proof. - [Application anatomy](https://cayu.dev/docs/get-started/project-anatomy/): inert imports, fresh factory, process roles and durable stores. - [Learn Cayu](https://cayu.dev/docs/learn/): 4 worked steps with executable code and fixtures. - [Worked example](https://cayu.dev/walkthrough/): public demo with 12 source excerpts, pinned separately from this release. ### Build and operate - [Concepts](https://cayu.dev/docs/concepts/) - [Build agents](https://cayu.dev/docs/build/) - [Evaluate](https://cayu.dev/docs/evaluate/) - [Operate](https://cayu.dev/docs/operate/) - [Recipes](https://cayu.dev/docs/recipes/) ### Reference and plain text - [Python API](https://cayu.dev/docs/reference/python/): declared exports, including optional capabilities. - [Python API JSON](https://cayu.dev/docs/python-api.json): small discovery index; select a namespace, then an alphabetic bucket for names and HTML/Markdown URLs. - [HTTP API](https://cayu.dev/docs/reference/http/) - [OpenAPI JSON](https://cayu.dev/docs/openapi.json): default server schemas; configured routes can vary. - [CLI](https://cayu.dev/docs/reference/cli/) - [Configuration](https://cayu.dev/docs/reference/configuration/) - [Runtime guarantees](https://cayu.dev/docs/reference/runtime-guarantees/) - [Page index](https://cayu.dev/docs/pages.json): every page and its plain Markdown URL. - [Complete manual](https://cayu.dev/llms-full.txt): guides and overview reference; detailed Python definitions are available through the page/API indexes. - [Release manifest](https://cayu.dev/docs/release.json): source version, checksum and coverage. A scripted provider proves fixture execution, not live-model quality. Native Python tools are trusted application code. External effects need domain receipts and reconciliation; session persistence alone does not prove exactly-once business effects. Hosted services are optional. - [Source](https://github.com/cayu-dev/cayu) - [Community](https://discord.gg/VUNHpjTDQ)