{"slug": "the-fx-adapter-now-runs-the-harness-on-the-host", "title": "The fx adapter now runs the harness on the host", "summary": "The fx adapter for the AI SDK's HarnessAgent now runs the harness and model requests in the same process as the application, using the libfx TypeScript library, while built-in filesystem and shell operations stay isolated in the sandbox. The rewrite removes the need to install fx inside the sandbox, run a sandbox bridge, or expose a sandbox port, and keeps model credentials on the host instead of forwarding them into the sandbox. It also adds built-in tool filtering, mid-turn steering, structured output, image tool results via toModelOutput(), and sessions that can be saved and resumed in a new host process; developers must update @ai-sdk/harness-fx to the latest version.", "body_md": "The fx adapter for the AI SDK’s `HarnessAgent` now runs the harness and model requests in the same process as your application. Built-in filesystem and shell operations remain isolated in the sandbox.\n\nThe adapter uses `libfx`, the TypeScript library for fx. It no longer needs to install fx inside the sandbox, run a sandbox bridge, or expose a sandbox port. Model credentials stay on the host rather than being forwarded into the sandbox.\n\nThe rewrite also adds:\n\n**Built-in tool filtering:** choose which built-in tools the agent can use\n\n**Mid-turn steering:** send new instructions while a turn is running\n\n**Structured output:** generate responses that match a schema\n\n**Image tool results:** return images to the model through `toModelOutput()`\n\nSessions can be saved and resumed in a new host process.\n\nUpdate `@ai-sdk/harness-fx` to the latest version to use the new adapter. Learn more in the [fx harness documentation](https://ai-sdk.dev/providers/ai-sdk-harnesses/fx).", "url": "https://wpnews.pro/news/the-fx-adapter-now-runs-the-harness-on-the-host", "canonical_source": "https://vercel.com/changelog/fx-harness-adapter-now-separates-host-and-sandbox", "published_at": "2026-10-27 06:00:00+00:00", "updated_at": "2026-10-28 04:42:31.380790+00:00", "lang": "en", "topics": ["ai-agents", "ai-tools", "developer-tools", "ai-safety"], "entities": ["AI SDK", "HarnessAgent", "fx", "libfx", "@ai-sdk/harness-fx"], "also_reported_by": [], "alternates": {"html": "https://wpnews.pro/news/the-fx-adapter-now-runs-the-harness-on-the-host", "markdown": "https://wpnews.pro/news/the-fx-adapter-now-runs-the-harness-on-the-host.md", "text": "https://wpnews.pro/news/the-fx-adapter-now-runs-the-harness-on-the-host.txt", "jsonld": "https://wpnews.pro/news/the-fx-adapter-now-runs-the-harness-on-the-host.jsonld"}}