VS Code moves agent sessions out of the editor and publishes the protocol under MIT

Microsoft shipped Visual Studio Code 1.133 on August 12, and the change worth reading closely is where agent code runs: AI agent sessions now execute in a dedicated background process called the Agent Host rather than inside the editor's extension host ^[1][2]. Microsoft also published the Agent Host Protocol (AHP) spec on GitHub under an MIT license, and positions it alongside the Language Server Protocol and Debug Adapter Protocol as infrastructure other tools can build on rather than a VS Code implementation detail ^[3][4].

The lifecycle consequence is the point. Because the host runs independently, several VS Code windows can attach to the same session and see a synchronized view ^[5], and sessions can be reached remotely over SSH or a dev tunnel ^[7]. Mitch Ashley, VP and practice lead for Software Lifecycle Engineering and AI-Native Software Engineering at The Futurum Group, told devops.com that the agent "no longer dies when one editor closes" and starts behaving like shared infrastructure ^[18]. That is the difference between an agent you babysit in a window and a long-running job you can walk away from.

The wire details suggest this was designed for more than one client. AHP uses JSON-RPC with immutable state and pure reducers, and each state change carries a sequence number so updates cannot arrive out of order ^[6]. Microsoft wrote first-party adapters for Copilot, Claude, and Codex that translate each runtime into the common AHP session model ^[8], which is the pattern LSP followed: one protocol, many backends, and the editor stops being the integration point.

Two smaller changes tell you what the abstraction is actually worth today. In Claude sessions you can now mix Anthropic and Copilot models in the same session, grouped under separate headings in the picker and chosen per turn, with Anthropic-listed models billing against your API key and Copilot-listed models drawing on your Copilot subscription ^[9][10]; previously, switching providers meant reconfiguring the agent host entirely ^[11]. Separately, an experimental setting, chat.agentHost.allowSignedOutWhenUsable, lets the Agents window open without a mandatory GitHub sign-in, attaching GitHub authentication to individual agents or models instead of gating the whole window ^[12][14]. That prompt previously blocked machines that could not reach github.com or users who did not want to authenticate against GitHub for an agent already configured with an API key ^[13]. It works only with Claude for now, with Copilot custom model keys and Codex promised in a future release ^[15] - one of the three shipped adapters, and two still waiting ^[22].

Operationally, VS Code will start a host for you, or you can run "code agent host" in a terminal to bring up a localhost server protected by a connection token, with a --tunnel flag to expose it for remote access ^[23][16]. Rollback exists: pre-existing sessions keep running under the old extension-host model, and setting chat.agentHost.enabled to false reverts the behavior entirely ^[17]. The release also adds sticky scroll for chat prompts, pinning the prompt you have scrolled past with click-to-jump and previous and next buttons ^[20], and the integrated browser now auto-refreshes local HTML files when they change on disk ^[21].

Watch for the first AHP client Microsoft did not write, because a spec with one implementation is a product decision, not infrastructure. Ashley reads the open spec as much a land grab as an engineering decision, according to devops.com ^[19]. Also watch the per-turn billing boundary, and whether teams exposing hosts through dev tunnels treat that connection token as sufficient control.