Agentic Design Patterns: The Shapes Every Coding Agent Reuses

This is an adapted excerpt from a guide in my AI Knowledge Hub. The full interactive version is linked at the end. Agentic design patterns are named control structures for arranging LLM calls and tools. This post gives you the decision rule for picking one, the exact shape of each pattern, and the cost each adds — so you can match a task to the minimum structure that solves it. Everything here is model-agnostic and grounded in Anthropic's Building Effective Agents and the Claude Agent SDK. Workflow vs. agent: the split that decides everything Anthropic divides all agentic systems into two categories, and the split decides every downstream tradeoff: Category Definition Control lives in Use when Workflow LLMs and tools orchestrated through predefined code paths Your code You can pre-map the decision tree; want accuracy, control, lower cost Agent LLMs dynamically direct their own processes and tool usage , maintaining control over how they accomplish tasks The model Open-ended task where you can't predict the number of steps Every pattern composes one unit: the augmented LLM — an LLM enhanced with retrieval, tools, and memory. It generates its own search queries, selects tools, and decides what to retain. If a single augmented LLM call solves the task, stop — no pattern required. The escalation rule is the whole game: find "the simplest solution possible, and only increasing complexity when needed" — which "might mean not building agentic systems at all." Agentic systems trade latency and cost for better task performance, so only escalate when a specific failure mode forces it. The agent loop: gather → act → verify → repeat For open-ended tasks, every agent runs the same four-beat loop: Gather context — read files, run agentic search ( grep / find / tail to pull relevant slices instead of whole files), or delegate to subagents with isolated context windows. Take action — execute via tools: bash, code generation, file edits, MCP servers. Verify work — check the result b