--- title: Making an Agent Harness Actually Model-Agnostic | daily.dev description: Most agent frameworks claim to be model-agnostic but only mean a config string that requires a restart to change. This post covers the design of pydantic-deep,... canonical: https://daily.dev/posts/making-an-agent-harness-actually-model-agnostic-owcjvkuy5 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Making an Agent Harness Actually Model-Agnostic | daily.dev og:description: Most agent frameworks claim to be model-agnostic but only mean a config string that requires a restart to change. This post covers the design of pydantic-deep,... og:url: https://daily.dev/posts/making-an-agent-harness-actually-model-agnostic-owcjvkuy5 og:image: https://api.daily.dev/og/posts/OWCJvKUy5.png og:image:alt: Making an Agent Harness Actually Model-Agnostic 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. # Making an Agent Harness Actually Model-Agnostic **[Medium](https://daily.dev/sources/medium_js)** · 8 min read · 0 upvotes · 0 comments ## Summary Most agent frameworks claim to be model-agnostic but only mean a config string that requires a restart to change. This post covers the design of pydantic-deep, an open agent harness built on Pydantic AI, that makes model switching truly live and persistent. Three controls get first-class treatment: /model (a fuzzy-searchable catalogue sorted by credentials you hold), /thinking (a six-level reasoning effort dial that persists across sessions), and /keys (a scoped keystore with global/project/env-var precedence). A key bug is highlighted: submodels like summarizers and reminder generators often fall back to hard-coded defaults, meaning switching the main model doesn't actually switch everything. The fix is a simple fallback chain where submodels inherit the primary model unless explicitly configured. Credential precedence, offline behavior, and layered config files are also discussed. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Building an Advanced Agentic Harness](https://daily.dev/posts/building-an-advanced-agentic-harness-oia5opvy8) · Hacker News · 0 upvotes · 0 comments - [Building AI Agents in Python with Pydantic AI](https://daily.dev/posts/building-ai-agents-in-python-with-pydantic-ai-aj0aokeuz) · Machine Learning Mastery · 4 upvotes · 0 comments - [How to Build Production-Grade Agents with Pydantic AI](https://daily.dev/posts/how-to-build-production-grade-agents-with-pydantic-ai-qbzy6k9o0) · freeCodeCamp · 1 upvotes · 0 comments - [Building an Agent with Pydantic AI](https://daily.dev/posts/building-an-agent-with-pydantic-ai-uvh89x786) · Medium · 1 upvotes · 0 comments --- Tags: [#python](https://daily.dev/tags/python), [#ai-agents](https://daily.dev/tags/ai-agents) [View this post on daily.dev](https://daily.dev/posts/making-an-agent-harness-actually-model-agnostic-owcjvkuy5) ```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":"Making an Agent Harness Actually Model-Agnostic","url":"https://daily.dev/posts/making-an-agent-harness-actually-model-agnostic-owcjvkuy5","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/making-an-agent-harness-actually-model-agnostic-owcjvkuy5"},"datePublished":"2026-07-12T10:51:37.634Z","dateModified":"2026-07-12T10:52:47.171Z","description":"Most agent frameworks claim to be model-agnostic but only mean a config string that requires a restart to change. This post covers the design of pydantic-deep,...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/1c12eb92f3365d77cc301fd0157b9986?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/1c12eb92f3365d77cc301fd0157b9986?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Medium","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":"Medium","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/medium","url":"https://daily.dev/sources/medium_js"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/making-an-agent-harness-actually-model-agnostic-owcjvkuy5","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"python,ai-agents","timeRequired":"PT8M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Medium","item":"https://daily.dev/sources/medium_js"},{"@type":"ListItem","position":3,"name":"Making an Agent Harness Actually Model-Agnostic"}]} ```