The ecosystem is a menu, not a ladder
There is no universal progression from raw loop to framework to multi-agent team. The right abstraction depends on which primitive you need to stop building yourself.
What each family buys
OpenAI Agents SDK buys OpenAI-native tools, handoffs, guardrails, tracing, and hosted-agent integration. LangGraph buys durable graph state, checkpointing, replay, human-in-the-loop, and low-level orchestration. CrewAI buys role/task configuration and team-oriented flows. Claude Agent SDK buys a developer harness with files, shell, MCP, permissions, and long-running session behavior. Smolagents buys code-as-action simplicity. A raw loop buys maximum control and minimum dependency surface.
Prefer boring until boring breaks
If one model and three tools solve the task, the raw loop is not primitive in the bad sense. It is inspectable. Add a framework when the missing primitive has a name and the framework handles it better than your team would.