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0021. Strengths build pools at load time and never remove a target

  • Status: accepted
  • Date: 2026-10-16
  • Supersedes: none
  • Change: openspec/changes/add-strengths-pools

Context

A route names its targets. The free pools of the reference deployment are described by a property ("the fastest free general model with at least 32,000 tokens of context"), so listing members by hand means every new free model has to be added to every route that should use it. Capabilities (ADR 0019) are hard facts that remove a target from a request only on certainty. What a model is good at is a judgment, and a wrong judgment must not refuse a request.

Decision

A target may declare strengths: up to 8 free-form lowercase labels (1 to 32 characters of letters, digits, - and _). A passthrough, fastest or random route may take pool = { strength = "...", min_context_window = N } instead of targets. Its targets are every target that carries the strength and, when a window is given, has at least one endpoint that declares a context_window of at least N, resolved when the configuration loads or reloads and written into the route's target list in target-name order. After that a pool is an ordinary route, so class, policy, capability and health removal and latency ordering act on it unchanged. Strengths remove nothing per request. An undeclared window does not qualify for min_context_window (this is the operator asking which targets are known to be big enough, the opposite question to request-time removal, which acts only on certainty); explain lists targets left out and why. A pool that resolves to nothing is a configuration error naming the strengths that exist; a reload that changes a pool's membership logs it.

Alternatives considered: matching strengths per request (membership would be non-deterministic, harder to explain and costs work on every call); a fixed vocabulary of strengths (blocks operators' own labels and buys little, since typos are caught by the empty-pool error); strengths on endpoints (they describe the model a route chooses, not a deployment's limits); treating an undeclared window as qualifying (it admits targets whose size is unknown into a pool defined by size); combining strengths with and/or in the first version (the reference use is a single label, and combinations can be added without breaking this form); fetching strengths from public data automatically (ADR 0014: public data is only ever a suggestion).

Consequences

A free pool is a property statement instead of a list, and a new free model joins it by being labelled. A wrong label costs a slightly different pool, visible in explain and fixed by one line, and never a refused request. Membership is fixed per configuration, so it is deterministic and explainable, and it changes only when the file does (a reload logs the change). A target whose context window is not declared is absent from size-limited pools until it is, which is stated rather than silent.