This piece assumes model SKUs are already mapped — it covers the Agents SDK orchestration layer. Full series in navigation below.
OpenAI’s Agents SDK shipped alongside the Responses API on March 11, 2025 as the orchestration framework for single- and multi-agent workflows. OpenAI’s own comparison is blunt: use Responses when you want to own the loop; use the Agents SDK when you want the SDK to run it.
Confirmed SDK role
- Manages the agent loop: repeated tool calls, branching, and stop conditions.
- Supports multi-agent patterns: handoffs and agents-as-tools with different instructions, tools, or policies per specialist.
- Adds productized controls OpenAI documents for SDK users: sessions / resumable run state, input-output-tool guardrails, approval pauses, and built-in tracing across model calls, tools, agents, and handoffs.
- Works with Responses and Chat Completions; OpenAI also documents interoperability with other providers that expose a Chat Completions–style endpoint.
Responses vs Agents SDK (OpenAI’s framing)
- Responses core abstraction: a model response — you compose tools, state, and branching.
- Agents SDK core abstraction: an agent run — the runner performs the tool loop and switches agents after handoffs.
- Tools: Responses exposes platform tools, function calling, and remote MCP; the SDK wraps those into reusable agents plus local MCP / tool wrappers.
- Debugging: Responses leans on response objects and API logs; the SDK adds end-to-end traces.
Where it sits in the stack
After dual-surface models and the Responses migration, the SDK is how OpenAI productizes “agent engineering” without forcing every team to reinvent orchestration. Computer use and hosted tools are what agents call; the SDK is how long-running work is structured.
Our take
In our view, the Agents SDK is OpenAI’s answer to a market that already built custom loops in Cursor-class IDEs and internal platforms. Selling the loop — not only the model — is how a lab stays the default platform when model names churn every summer.
Series: OpenAI Product Stack · next: computer use & built-in tools.
