--- title: The fx adapter now runs the harness on the host | daily.dev description: The fx adapter for the AI SDK's HarnessAgent now runs the harness and model requests on the host, while filesystem and shell operations stay isolated in the... canonical: https://daily.dev/posts/the-fx-adapter-now-runs-the-harness-on-the-host-b3opr2jz7 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: The fx adapter now runs the harness on the host | daily.dev og:description: The fx adapter for the AI SDK's HarnessAgent now runs the harness and model requests on the host, while filesystem and shell operations stay isolated in the... og:url: https://daily.dev/posts/the-fx-adapter-now-runs-the-harness-on-the-host-b3opr2jz7 og:image: https://api.daily.dev/og/posts/b3OPR2JZ7.png og:image:alt: The fx adapter now runs the harness on the host og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # The fx adapter now runs the harness on the host **[Vercel](https://daily.dev/sources/vercel)** · 1 min read · 1 upvotes · 0 comments ## Summary The fx adapter for the AI SDK's HarnessAgent now runs the harness and model requests on the host, while filesystem and shell operations stay isolated in the sandbox. The fx adapter now uses libfx, the TypeScript library for fx. This simplifies sandbox setup, so you no longer need to install fx inside the sandbox, run a sandbox bridge, or expose a sandbox port. Model credentials stay on the host, outside the environment where the agent executes commands. The update also adds built-in tool filtering, mid-turn steering, structured output, and image tool results via toModelOutput(). Sessions can now be saved and resumed in a new host process. Update @ai-sdk/harness-fx to get the new adapter. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### what changed in the ai-sdk fx harness adapter architecture The fx harness adapter now runs the harness and model requests on the host application process instead of inside the sandbox, using libfx, the TypeScript library for fx. Filesystem and shell operations stay isolated in the sandbox. This 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. _Developers wiring up agent sandboxes can track AI SDK infrastructure changes like this on daily.dev._ ### how do I update to the new ai-sdk fx harness adapter Update the @ai-sdk/harness-fx package to its latest version to get the new host-based adapter. The rewrite also adds built-in tool filtering, mid-turn steering, structured output support, and image tool results returned through toModelOutput(), plus the ability to save and resume sessions in a new host process. _Anyone upgrading agent harness dependencies can follow releases like this on daily.dev._ ## Similar posts on daily.dev - [HarnessAgent now supports image inputs for all harness adapters](https://daily.dev/posts/harnessagent-now-supports-image-inputs-for-all-harness-adapters-ffpbo7bq4) · Vercel · 1 upvotes · 1 comments - [The Agent Harness Belongs Outside the Sandbox](https://daily.dev/posts/the-agent-harness-belongs-outside-the-sandbox-svquzjusi) · Hacker News · 0 upvotes · 0 comments - [Bringing more agent harnesses and frameworks to Cloudflare, starting with Flue](https://daily.dev/posts/bringing-more-agent-harnesses-and-frameworks-to-cloudflare-starting-with-flue-zzfesfefy) · Cloudflare · 2 upvotes · 0 comments --- Tags: [#typescript](https://daily.dev/tags/typescript), [#vercel](https://daily.dev/tags/vercel), [#agentic-ai](https://daily.dev/tags/agentic-ai), [#ai-sdk](https://daily.dev/tags/ai-sdk) [View this post on daily.dev](https://daily.dev/posts/the-fx-adapter-now-runs-the-harness-on-the-host-b3opr2jz7) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"The fx adapter now runs the harness on the host","url":"https://daily.dev/posts/the-fx-adapter-now-runs-the-harness-on-the-host-b3opr2jz7","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/the-fx-adapter-now-runs-the-harness-on-the-host-b3opr2jz7"},"datePublished":"2026-10-29T17:24:07.750Z","dateModified":"2026-10-29T17:34:31.751Z","description":"The fx adapter for the AI SDK's HarnessAgent now runs the harness and model requests on the host, while filesystem and shell operations stay isolated in the...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/ea39a6b90c81691c652fa01c992a9303?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/ea39a6b90c81691c652fa01c992a9303?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Vercel","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Vercel","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/04cca7235cf84db092f24b7ba427b3e1","url":"https://daily.dev/sources/vercel"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/the-fx-adapter-now-runs-the-harness-on-the-host-b3opr2jz7","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"typescript,vercel,agentic-ai,ai-sdk","timeRequired":"PT1M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Vercel","item":"https://daily.dev/sources/vercel"},{"@type":"ListItem","position":3,"name":"The fx adapter now runs the harness on the host"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/the-fx-adapter-now-runs-the-harness-on-the-host-b3opr2jz7#faq","mainEntity":[{"@type":"Question","name":"what changed in the ai-sdk fx harness adapter architecture","acceptedAnswer":{"@type":"Answer","text":"The fx harness adapter now runs the harness and model requests on the host application process instead of inside the sandbox, using libfx, the TypeScript library for fx. 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