Tiers vs. Pinned Models: Two Ways to Control What Your Agent Runs On
Why did the agent use that model for this request? Two separate control layers answer that — a default tier and a per-intent pin — and it's worth knowing which one you're actually configuring.
"Why did it use that model for this" is one of the most common points of confusion once a platform gives you any control over model selection at all. Here, there are genuinely two separate layers doing that job, and understanding the difference saves you from configuring the wrong one and wondering why nothing changed.
The default layer: tiers
Every kind of request the agent might make — a router intent, in the platform's terms — has a default model tier associated with it. This is the baseline: absent any more specific instruction, this is what a given kind of request runs on. It's a sensible default, not a setting you're expected to touch constantly, and it's what most requests actually use day to day.
The override layer: pinned models
On top of that default sits a per-intent override — a pin. If you want a specific kind of request to always use a specific model, regardless of what the tier default would otherwise select, a pin is how you say that explicitly. Pins live separately from tier defaults specifically so that an override is visible as an override, not buried inside a change to the default behavior for everyone.
Why the two-layer design, instead of just one setting
A single global "default model" setting sounds simpler, but it can't express "use a cheaper model for routine summarization but a stronger one for anything customer-facing" — which is exactly the kind of distinction real usage needs. Splitting default behavior (tiers) from deliberate overrides (pins) lets you leave most request types on a sensible default while being precise about the handful that actually need something specific.
The practical takeaway
If your agent is using a model you didn't expect, the fix depends on which layer is actually driving that choice: check whether there's a pin already set for that specific kind of request before assuming the tier default needs to change — changing the tier affects every request of that kind that doesn't already have its own pin, while adding a pin affects only the one you're trying to fix.