This article remains one of the better pieces on this topic, especially since it clearly defines which definition of "AI agents" they are using at the start! They use: "systems where LLMs dynamically direct their own processes and tool usage, maintaining control over how they accomplish tasks".
I also like the way they distinguish between "agents" and "workflows", and describe a bunch of useful workflow patterns.
I published some notes on that article when it first came out: https://simonwillison.net/2024/Dec/20/building-effective-age...
A more recent article from Anthropic is https://www.anthropic.com/engineering/built-multi-agent-rese... - "How we built our multi-agent research system". I found this one fascinating, I wrote up a bunch of notes on it here: https://simonwillison.net/2025/Jun/14/multi-agent-research-s...
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