The Litmus Test¶
The decision it resolves: is a given pattern genuinely new, or a familiar one wearing an "agentic" costume?
Most of what gets sold as a new "agentic pattern" is an ordinary design pattern with a language model dropped into one slot. A few are genuinely new. One question tells them apart, and it is the spine of this whole reference:
Who makes the structural decision: the model, or your code?
If the model makes the call, it is genuinely new. It decides to reach for a tool, judges its own draft and loops, sizes its own work, or picks which kind of expert to reason as. Nothing in the pre-LLM toolbox could make a judgement call in the middle of a control flow.
If your code makes the call and the model is just the worker inside the structure, it is a pattern you already know. A lookup that routes a request, a loop that retries on failure, a callback that fires when a step finishes. Useful, necessary, and not new.
This is a classification lens (is it new?), not a quality one (is it proven?). The two are orthogonal axes, and How We Label carries the second. When in doubt, downgrade the claim.
The full treatment is 1.2 Who Decides?: the four "model decides" tells, the honest three-way split (four genuinely new, four just engineering, three that are not patterns, and one honest draw), the dispatcher-is-not-routing deflation, and why mislabelling changes what a system costs and how you have to test it.
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