Microsoft has released Visual Studio Code 1.129, and the headline change isn’t a new feature so much as a new foundation. The update introduces the agent host, a dedicated process that runs AI coding agents like Copilot, Claude, and Codex outside the editor itself, using a new open protocol called the Agent Host Protocol (AHP).
That distinction matters more than it sounds. Until now, agent sessions in VS Code lived inside the extension host, tied to the lifecycle of a single window. Close the window, and the session’s context went with it. The Agent Host Protocol is an open, agent-agnostic protocol between a host and its clients that uses JSON-RPC for communication and immutable state with pure reducers for synchronized session data. In practice, that means an agent session becomes something closer to a resource on a server than a temporary artifact of one editor window.
The host owns agent sessions independently of the clients that display and control them, which gives VS Code two capabilities it didn’t have before: shared sessions, where multiple clients can observe and control the same session while staying in sync, and remote execution, where the host runs next to the workspace on a separate machine while clients connect from elsewhere. A developer could start a long-running agent task from a laptop, close it, and pick the same session back up from a different machine without losing state. The defining principle behind the design is that the agent can run without a client attached at all.
Mitch Ashley, VP and practice lead for software lifecycle engineering and AI-native software engineering at The Futurum Group, says the change addresses a problem developers have been living with for a while. “Decoupling agent sessions from the editor process solves a real problem. Engineers used to lose context whenever a window closed. Teams running agents across hybrid environments now need sessions that outlive any single laptop.”
Microsoft built the agent host with contributions from outside its own walls. The agent host’s Copilot agent is powered by the Copilot SDK, which aligns its behavior with the Copilot CLI, the standalone GitHub Copilot app, and other Copilot products, so the same underlying engine now shows up consistently across Microsoft’s Copilot surface area rather than behaving differently depending on where you access it.
To turn the agent host on, developers enable the chat.agentHost.enabled setting and pick a harness from a dropdown in either the editor window or the newer Agents window. Microsoft is rolling it out gradually rather than flipping it on for everyone at once, which tracks with how it has handled other structural changes to VS Code’s chat and agent features over the past year.
The release bundles several features that build directly on that new architecture. Sessions running on the agent host now get access to session-management tools, letting one agent list, inspect, and hand off work to other sessions without a developer needing to switch context manually. Any time a tool creates or targets a session, VS Code shows an “Open Session” pill, and sending a message to another session always requires confirmation first — a guardrail against an agent quietly fanning a single task out into a pile of unsupervised sessions.
The Agents window also gets an experimental new editor panel that docks a session’s files and diffs alongside its chat in one pane, plus a redesigned diff view with inline and side-by-side toggles. Chat picked up a ! prefix for running terminal commands directly from a prompt, and GitHub Enterprise users can now authenticate Copilot through their own GHE instance rather than being limited to github.com — a gap that previously blocked Enterprise-backed Copilot subscriptions from completing sign-in at all. Rounding out the release is an early, opt-in preview of a modernized VS Code UI, available now in Insiders builds.
None of these individually reads as a blockbuster. Together, they describe a strategy: keep agent orchestration open and protocol-based rather than locking it to one vendor’s tooling. That openness is also the bet Microsoft is making against competitors. VS Code’s answer to the agentic IDE competition is not a better completion engine or a more autonomous agent loop — it’s an open harness, where BYOK works with any provider, AHP is a public protocol with open SDKs, the extension marketplace carries thousands of existing integrations, and the enterprise plugin layer gives administrators a governance mechanism that scales across an organization.
For IT leaders, the part of this release worth tracking closely is what multi-client sessions mean once agents move beyond a single developer’s laptop. Ashley frames it as an audit problem as much as an architecture one. “Multi-client session control turns this into a governance question. Audit trails now have to separate who observed a session from who acted on it. Regulated organizations can’t wait for an incident to find out which was which.”
VS Code is rolling out 1.129 gradually through its built-in update mechanism, with the full feature set — including the agent host — available now to Insiders users who want early access.
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