> ## 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.

# What's in v4

> Find the v4 capabilities, adapters, and migration steps in one place.

Agentium 4.0.0 introduces a standalone harness package and expands execution, voice, telephony, and operations. Use this page to find the guide for each release area; use the [migration guide](/migration-v4) when upgrading an existing application.

## Compose execution with @agentium/harness

[Define a harness](/harness/definitions) from abilities and context sources, select an [execution driver](/harness/drivers), and enforce [grants, budgets, and policies](/harness/policies). The package owns its [sessions](/harness/sessions), [events](/harness/events), [portable manifests](/harness/manifests), and [watches](/harness/watches). Start with the [research recipe](/examples/harness-research) or [workspace reviewer](/examples/harness-workspace).

The old agent-embedded harness API is removed. Import the package from `@agentium/harness`; see [harness migration](/harness/migration).

## Connect voice and phone systems

| Capability | Guides |
| - | - |
| Outbound call control | [Twilio](/telephony/twilio), [Telnyx](/telephony/telnyx), [SignalWire](/telephony/signalwire), [Vonage](/telephony/vonage), [Exotel](/telephony/exotel), [LiveKit SIP](/telephony/livekit) |
| Streaming recognition and synthesis | [OpenAI](/voice/openai), [ElevenLabs](/voice/elevenlabs), [Sarvam](/voice/sarvam) |
| Native realtime conversation | [OpenAI and Gemini adapter choices](/voice/adapters), [voice sessions](/voice/overview) |
| Room audio | [LiveKit media transport](/voice/livekit) |
| Interrupted and uncertain work | [Voice recovery](/voice/recovery), [call callbacks and reconciliation](/telephony/callbacks) |

## Control longer-running work

[Durable records](/durable/records) cover tasks, actions, approvals, events, and artifacts. [Queue integration](/queue/durable), [protocol bridges](/durable/protocols), and [watches](/durable/watches) connect those records to workers and external systems. Follow [recovery guidance](/ship/recovery) before retrying an operation that may already have had an effect.

## Run and observe integrations

* [Sandbox backends](/sandbox/overview): local execution, E2B, and Daytona have explicit ownership and dependency contracts.
* [Telemetry exporters](/observability/exporters): JSONL files, OTLP/HTTP JSON, a host-owned OpenTelemetry tracer, and Langfuse OTLP.
* [Transport](/transport/overview): caller scope and authentication, bounded streaming, multipart cleanup, and Socket.IO session ownership.
* [Evaluation](/eval/overview): cancellation, deadlines, case identity, and assertion results.
* [MCP](/mcp/v2): approved text resources have URI, MIME, and ownership constraints; [harness context](/harness/context) explains how to consume them.
* [Tools](/agents/tools): schema support includes Zod 3, Zod 4 Classic, and Zod 4 Mini. [Skills](/skills/overview) cover file and package validation.

## Upgrade the application

Use supported [Node and package versions](/learn/installation), migrate the [removed v3 APIs](/migration-v4), and check [BullMQ compatibility](/queue/migration). Model versions are provider choices, recorded separately in [Example models](/reference/example-models).


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