# OpenAI Agents SDK: Building with Model-Native Harnesses _OpenAI's latest Build Hour session dives into the updated Agents SDK, showcasing new features like a Codex-style harness and enhanced sandboxing capabilities._ **Updated:** 2026-08-22 **Published:** 2026-05-28 **Source:** https://www.startuphub.ai/ai-news/artificial-intelligence/2026/openai-agents-sdk-building-with-model-native-harnesses --- In a recent "Build Hour" session, OpenAI showcased significant advancements in its Agents SDK, a toolkit designed to empower developers in building sophisticated AI agents. The session, hosted by Christine Jones and Steve Corley from OpenAI, highlighted key updates and new features that streamline the development process and unlock greater capabilities for AI agents. OpenAI Build HourCoresession focused on the updated Agents SDK and its capabilitiesFrom the article 2 mentionsIn a recent "Build Hour" session, OpenAI showcased significant advancements in its Agents SDK, a toolkit designed to empower developers in building sophisticated AI agents.showcasesAgents SDK UpdatesCoreshowcasing new features and enhancements for AI agent developmentFrom the article 9+ mentionsThis particular session focused on the Agents SDK, providing a deep dive into its enhancements and demonstrating how developers can leverage these updates to create more capable and adaptable AI agents.Model-Native HarnessCoreCodex-style harness for enhanced functionality and capabilitiesFrom the article 5 mentionsThe Agents SDK is built around a "model-native harness," meaning the core loop, tools, and execution are handled by the SDK itself.Enhanced SandboxingContextimproved security and control for AI agent execution environmentsNew ToolsEffectcapabilities introduced to streamline agent building and deploymentFrom the article 6 mentionsThe primary goal of OpenAI's Build Hour sessions is to equip developers with the best practices, tools, and AI expertise to scale their companies using OpenAI's APIs and models.Empowering DevelopersEffectenabling creation of more capable and adaptable AI agentsFrom the article 9+ mentionsThe SDK now offers greater flexibility in deployment, allowing developers to choose where their agents run.demonstrated byTask Tracker DemoOutcomepractical example of building an AI agent with the SDKFrom the articleDuring the session, Steve Corley provided a live demonstration of how to build a task tracker using the Agents SDK. ## Empowering Developers with the Agents SDK The primary goal of OpenAI's Build Hour sessions is to equip developers with the best practices, tools, and AI expertise to scale their companies using OpenAI's APIs and models. This particular session focused on the Agents SDK, providing a deep dive into its enhancements and demonstrating how developers can leverage these updates to create more capable and adaptable AI agents. The full discussion can be found on **OpenAI Youtube**'s YouTube channel. ![Build Hour: Agents SDK - OpenAI Youtube](https://img.youtube.com/vi/tK32trvj_b4/maxresdefault.jpg) Build Hour: Agents SDK, from OpenAI Youtube ## Key Updates and Features Steve Corley, an engineer on the OpenAI API team, detailed several key improvements to the Agents SDK. A significant highlight is the introduction of a "Codex-style harness," which provides a more integrated approach to agent control, adaptability, and reliability. This harness aims to simplify the complex orchestration and maintenance often associated with building agent-based systems. The SDK now offers greater flexibility in deployment, allowing developers to choose where their agents run. This includes executing agents within sandboxed environments, such as Docker containers, or leveraging cloud infrastructure like Modal or Cloudflare. This separation of harness from compute is crucial for security, durability, and scalability, ensuring that sensitive information and agent states are managed effectively and do not interfere with the underlying system. Corley also emphasized the improved capabilities of the models themselves, noting that they are becoming increasingly adept at completing real-world tasks over extended periods. Examples like "Codex," "The Codex security agent," and "OpenAI's internal data analysis agent" were presented, showcasing how models can now perform tasks end-to-end, analyze complex codebases for vulnerabilities, and process data analysis requests in minutes. ## A Model-Native Harness for Enhanced Functionality The Agents SDK is built around a "model-native harness," meaning the core loop, tools, and execution are handled by the SDK itself. This design allows developers to focus on describing the task and letting the agent figure out the implementation details. The SDK's open-source and customizable nature further empowers developers to shape it to their specific infrastructure and workflows. Key features of the Agents SDK include: - **Codex-inspired harness:** Borrowing from the capabilities of Codex, this framework provides essential tools for agent development. - **Sandboxes:** Agents can be run in isolated, reproducible environments, supporting shared workflows and granular control over resource access. - **Open-source and customizable:** Developers can pick their ideal setup, leverage existing tools, and bring their own data and models. ## New Tools and Capabilities OpenAI has also introduced several new tools and capabilities within the SDK: - **Hosted Shell tool:** This allows running CLI-grade tasks inside an isolated container via the Responses API, useful for build/test steps, linting, and deterministic workflows. - **Network-enabled Containers:** Developers can now control outbound network access for containers, enabling agents to interact with external services when explicitly allowed. - **Skills API:** This feature allows developers to package reusable, versioned workflows into "skills" that agents can mount and utilize. These skills are managed via a manifest file and can be easily updated and versioned. - **Typescript availability:** The SDK now offers Typescript support for sandbox agents, further enhancing the developer experience for those working with this language. ## Demo: Building a Task Tracker During the session, Steve Corley provided a live demonstration of how to build a task tracker using the Agents SDK. The demo showcased the process of creating an agent, defining its capabilities, and utilizing skills to interact with files and external services. The agent was able to process provided files, create program assets, and provide output logs, illustrating the SDK's practical application in automating complex workflows. The demo highlighted the ability to upload files to the agent's sandbox, have the agent process them using defined skills, and then return the results. This end-to-end demonstration underscored the power and flexibility of the Agents SDK in building sophisticated AI-powered applications. --- Original analysis from [startuphub.ai](https://www.startuphub.ai), the #1 AI startup directory. © StartupHub.ai. All rights reserved. You may not republish this article in full without a license. Search engines and AI research tools may crawl and summarize for reference. Bulk reproduction or model training on this content requires a license. See https://www.startuphub.ai/terms.