VS Code Agent Host: Running Copilot, Claude, and Codex in a Dedicated Process

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VS Code version 1.129 introduces a dedicated agent host process for managing AI coding assistants with isolated execution environments.

Key Features of the Agent Host

Isolated Execution Environment

A new architectural update in Visual Studio Code version 1.129 introduces a dedicated agent host process to manage AI coding assistants. This change enables multiple editor windows to share a single agent session while maintaining process isolation.

Agent Host Protocol

The agent host operates under the Agent Host Protocol framework, allowing sessions to span across multiple VS Code instances simultaneously. The Copilot agent within the host leverages the Copilot Software Development Kit, ensuring consistency with the Copilot Command Line Interface and standalone GitHub Copilot application.

User Access and Configuration

User access to this feature requires activation of the chat.agentHost.enabled setting, which is managed by organizational administrators. Once enabled, users can select from available harnesses through a configuration dropdown.

User Experience Enhancements

Redesigned Agents Panel

A redesigned agents panel consolidates editing and detail views into a unified dockable pane with shared tab management. This interface supports file and diff visualization alongside chat interactions, with a Changes view offering inline and side-by-side diff options.

Session State Persistence

Session state persistence ensures that side-pane dimensions, open editors, active files, and per-file collapse settings are retained across window reloads. This experimental layout is activated via the sessions.layout.singlePaneDetailPanel setting, which is evaluated once when the window initializes.

Agent Session Management

Agent session management capabilities allow assistants to interact with other sessions. Functions include listing active sessions with status indicators, accessing conversation history, initiating new tasks, and transmitting directional messages between sessions. The system displays an “Open Session” indicator when sessions are created or targeted through external tools.

Advanced Functionality and Customization

Message Transmission and Security

Message transmission between sessions requires explicit confirmation to prevent unauthorized communication. A rate-limiting mechanism restricts rapid message bursts to maintain session integrity.

Terminal and Git Integration

Terminal command execution now supports the “!” prefix, allowing chat prompts to trigger terminal operations within agent host sessions. A unified “New Worktree” checkbox enables Git worktree isolation, separating agent changes into distinct folders until integration.

Custom Editors and UI

Custom editors now opt out of diff and merge interfaces by default, ensuring files open in native text editors while diffs use built-in viewers. A new customEditorPriority API provides extension developers with separate priority configurations for files, diffs, and merge editors, including a “never” option for manual selection scenarios.

Enterprise and Developer Tools

Enterprise Authentication

Custom key models function within the Copilot harness, with enterprise users able to authenticate against internal GitHub instances. Previously restricted OAuth flows now accommodate enterprise host domains.

Modern UI Preview

An experimental Modern UI preview alters the editor’s visual layout, available by default in Insiders builds. This update includes redesigned interfaces for improved usability and visual clarity.