A Guide to Which AI to Use in the Agentic Era

2025-06-23 · Source: One Useful Thing · Field: Technology & Digital — Artificial Intelligence & Machine Learning, Software Development & Engineering, Data Science & Analytics · Depth: Intermediate, medium

Summary

The landscape of AI usage has dramatically shifted from simple chatbot interactions to AI acting as agents capable of performing multi-step tasks using various tools. This evolution necessitates considering three key components when selecting an AI: Models, Apps, and Harnesses. Models, such as Claude Opus 4.6, GPT-5.2/5.3, and Gemini 3 Pro, represent the underlying AI intelligence, determining reasoning and capability. Apps are the user interfaces, like chatgpt.com or claude.ai, which bundle features like image/video creation, deep research, or guided learning. Harnesses are systems that empower AI models to use tools, take actions, and complete complex tasks autonomously, significantly enhancing their utility beyond basic chat. For instance, Claude Code provides a virtual computer and browser for coding, while Claude Cowork handles non-technical desktop tasks. The article emphasizes that the same model can perform vastly differently depending on the app and harness it operates within, making the choice of these components crucial for effective AI application.

Key takeaway

For AI Product Managers evaluating new tools, recognize that the shift from chatbots to agentic AI fundamentally alters how value is delivered. Your decision on "which AI to use" must now encompass the model's intelligence, the app's bundled features, and critically, the harness's ability to enable autonomous, multi-step task execution. Prioritize solutions with robust harnesses for real-world problem-solving, as this directly impacts the AI's practical utility and your team's productivity.

Key insights

AI use has evolved from chatbots to agents, making model, app, and harness selection critical for task performance.

Principles

• Paid AI models offer superior accuracy and capability over free versions.
• Harnesses significantly expand AI model utility beyond basic chat.
• Model performance varies greatly based on the app and harness used.

Method

When selecting an AI, consider the interplay of Models (core intelligence), Apps (user interface and bundled features), and Harnesses (tool-access and task automation systems) to match the AI's capabilities to specific task requirements.

In practice

• Pay for advanced AI models for serious work.
• Manually select specific advanced models like GPT-5.2 Thinking Extended.
• Experiment with agentic apps like Claude Code or NotebookLM for complex tasks.

Topics

• AI Agents
• Large Language Models
• AI Applications
• AI Harnesses
• Generative AI Workflows

Best for: Software Engineer, Data Scientist, AI Product Manager

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Editorial summary, takeaway, and curation by AIssential. Original article published by One Useful Thing.