Agent frameworks and SDKs are the infrastructure for building multi-agent systems. These tools provide orchestration primitives — task routing, memory management, tool calling, agent-to-agent communication, and workflow state — so developers don't have to implement these from scratch for every application.

The ecosystem spans a spectrum from lightweight SDK wrappers (a thin abstraction over LLM APIs with tool calling) to full orchestration platforms (visual workflow builders, multi-agent routing, human-in-the-loop checkpoints). Choose based on how much control you need versus how fast you want to ship.

Key signals when evaluating agent frameworks: does it support multiple LLM backends? How does it handle failures and retries? Does it have an observability story (tracing, logging, cost tracking)? Is there a path from prototype to production without a full rewrite? The best frameworks make the easy cases easy and the hard cases possible.