VS Code 1.129 Ships Agent Host Protocol and Modern UI Preview

Two Releases in One Week

Microsoft shipped Visual Studio Code 1.129 on 15 July 2026 and followed it three days later with a 1.129.1 servicing update on 17 July — two releases in one week, each carrying changes that materially affect how development teams run AI agent sessions inside the editor. The headline architectural change is the Agent Host Protocol, which extracts AI agent sessions from the extension process and moves them into a dedicated background process that can be connected to from multiple editor windows. VS Code 1.129 also ships a redesigned Agents panel with a docked diff view, terminal command execution directly from the chat input, and Bring Your Own Key model support for the Copilot harness within the agent host. The 1.129.1 patch adds stability fixes and enables an experimental Modern UI preview that replaces the flat workbench chrome with floating card panels.

The Agent Host Protocol: AI Sessions Leave the Extension Sandbox

The Agent Host Protocol is the most significant architectural change in the 1.129 release cycle. Microsoft is moving all supported coding-agent sessions — GitHub Copilot, Claude, and OpenAI Codex — out of extension processes and into a dedicated background process called the agent host. The key practical effect is that an agent session started in one editor window can be attached to from a different window. A developer working across a large monorepo can start a long-running agent task from a terminal-heavy layout, then switch to a documentation-focused layout in a second window and continue interacting with the same session without losing context or duplicating work. The agent host also isolates agent sessions from the main editor process, which means a misbehaving or long-running agent cannot freeze or crash the editor window the developer is actively working in.

BYOK and Enterprise Authentication

VS Code 1.129 extends agent host support to Bring Your Own Key models. Teams that want to route Copilot agent sessions through their own Azure OpenAI or Anthropic API endpoints — rather than GitHub-hosted inference — can now do so within the full agent host architecture. The release also adds GitHub Enterprise authentication for the Copilot harness in the agent host, closing a gap that had blocked some corporate GitHub Enterprise environments from adopting the agent host. Both changes are significant for organisations operating AI tools under enterprise agreements with data residency obligations, model vendor mandates, or audit trail requirements.

The Redesigned Agents Panel

VS Code 1.129 ships a redesigned Agents panel with a docked diff view on the right side. When an agent proposes file changes, the diff renders in a persistent panel rather than a temporary modal or floating overlay, allowing developers to review multiple proposed edits sequentially while keeping the agent conversation in view. A new command in the chat input — prefixing a line with an exclamation mark — allows terminal commands to execute directly from the agent conversation, removing the need to switch to the integrated terminal during an agent-assisted workflow. Together, the docked diff and in-chat terminal execution reduce the number of context switches required during a typical agent-driven coding or refactoring session.

Modern UI Preview in VS Code 1.129.1

The 1.129.1 update enables an experimental Modern UI preview. Activated via the workbench.experimental.modernUI setting, the preview replaces the editor's flat, edge-to-edge workbench chrome with floating card panels: sidebars and the bottom panel render as separate floating cards with rounded corners and visible gaps between them, rather than the flush, edge-to-edge panels of the current design. The floating card layout is already the default in VS Code Insiders — Microsoft's pre-release build — and is off by default in the stable channel. Microsoft flags it as experimental, and teams can opt in now to evaluate it ahead of a potential future stable default.

What This Means for Development Teams

The Agent Host Protocol addresses a specific friction point in long-horizon agentic workflows: the tight coupling between an agent session and a single editor window. Until 1.129, if a developer switched workspace layouts or opened a second editor window while an agent task was in progress, the agent session context was locked to the original window. With agent host sessions, the session persists independently of any particular window layout, making it easier to manage parallel agent tasks across large multi-module codebases or to hand off a running session between collaborators in a remote development environment.

For Indian software development teams — particularly those at IT services companies or regulated-sector product companies where AI tool inference must stay within a specific cloud environment — the BYOK extension to the agent host is directly applicable. Enterprise teams can now use the full multi-window agentic session architecture while routing all model calls through their own governed endpoints, combining the developer experience improvements in VS Code 1.129 with the data residency controls their compliance obligations require.

The Bottom Line

VS Code 1.129 (15 July) and 1.129.1 (17 July 2026) introduce the Agent Host Protocol, which moves AI agent sessions for Copilot, Claude, and Codex into a dedicated background process that can be attached from multiple editor windows simultaneously. The releases also ship a redesigned Agents panel with a docked diff view, in-chat terminal command execution, BYOK model routing for enterprise teams, and GitHub Enterprise authentication for the Copilot harness. VS Code 1.129.1 adds an experimental Modern UI preview that renders the workbench as floating card panels. Together, the two releases move VS Code's AI layer from extension-embedded sessions to a proper multi-window agent runtime, materially reducing friction in long-horizon agentic development workflows.