> ## Documentation Index
> Fetch the complete documentation index at: https://docs.agentium.in/llms.txt
> Use this file to discover all available pages before exploring further.

# Agentium 4.0.0 and upgrades

> Understand the v4 package boundary, breaking changes, and documentation verification.

These docs target **Agentium 4.0.0**. All ten Agentium packages use the same release version, including the new `@agentium/harness`. Install matching versions and read the [v4 migration guide](/migration-v4) before upgrading from 3.x.

| Application baseline | Where to start |
| - | - |
| New v4 application | [Installation](/learn/installation), then the [quickstart](/quickstart) |
| Existing 3.x application | [Migrate to v4](/migration-v4), then the guide for each changed integration |
| Existing 2.x application | Historical [v3 migration](/migration-v3), followed by [v4 migration](/migration-v4) |
| SDK development checkout | Build related packages from one revision and verify declarations; a version string alone does not identify local changes |

## What changes in v4

* **Separate harness package.** Definitions, abilities, drivers, runtime controls, policies, manifests, and watches live in [`@agentium/harness`](/harness/overview). Core exposes a neutral execution-services contract.
* **Explicit execution boundaries.** Workspace read/write mode and local/authenticated hosting mode must be chosen. Removed Agent entrypoints and protocol aliases have replacements in the migration guide.
* **Broader schema support.** Public tools and structured output accept Zod 3, Zod 4 Classic, and Zod Mini. Use schema helpers when inspecting parameters.
* **Opt-in durable systems.** Tasks, actions, approvals, event/artifact records, queue delivery, protocol bridges, and watches have explicit storage and recovery contracts.
* **Updated integrations.** Voice and telephony, MCP/A2A protocols, BullMQ migration, sandbox adapters, evaluators, and metadata-first telemetry have updated contracts.
* **Runtime support.** Node.js `^22.18.0` or `^24.11.0`.

See the [v4 migration table](/migration-v4) for exact removed names and behavior changes. Ordinary Agent calls do not automatically become durable or gain distributed recovery when you upgrade.

## What the docs checks establish

Docs maintenance checks page structure, navigation, links, public SDK imports, and complete TypeScript examples. The support tutorial embeds checked source files. The harness reference is generated from public declarations and checks every export in both package entrypoints.

Local declaration checks and credential-free fixture runs do not establish that every provider or hosted integration has been exercised. Voice devices, Redis, MongoDB, carrier calls, push verification, and external-effect reconciliation need integration-specific validation.

Maintainers also verify exact public package versions before testing released tarballs. Release artifact availability and local source verification are separate checks; neither should be inferred from a successful MDX build.


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