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Model and effort resolve through the same configuration layers ​

Context ​

Which model answers a request, and how much of its time budget goes to thinking, are decisions people want to make at different granularities: this one message, this thread, me, this channel, this installation, this agent. Early versions hardcoded a model per agent and treated reasoning effort as a detail of the model call. Both were wrong. An agent's real budget is wall-clock time, and effort decides how much of that goes to thinking rather than to work, so it is a routing decision of the same rank as the model.

Decision ​

Model references are <provider>/<model> strings and effort is a named tier. Both resolve through one ladder, highest wins:

  1. a directive on the request (model:…, effort:…)
  2. the thread's sticky choice, derived from the thread's history and never stored
  3. the user's configuration
  4. the channel's configuration
  5. the installation defaults in config/config.yaml
  6. the agent definition
  7. the provider default

An agent's registry effort is a floor every layer above can override, never a hardcoded tier. Runtime overrides set from chat persist to the state Worker's ConfigDO so they survive container restarts. Custom instructions ride the same scopes but are prompt content only; they never change resolution or gates.

Consequences ​

  • Nothing in an agent or the core names a model or an effort.
  • A thread keeps the model it started with because the choice is re-derived from history on every turn; there is no per-thread record to lose or clean up.
  • The same ladder later carried per-scope custom instructions and per-scope memory without a new mechanism.
  • Seven layers is a lot to explain. The config show command prints the resolved value with the layer it came from, and the explanation doc on config layers walks the ladder.

Alternatives rejected ​

  • Effort as a model detail. A claude-…-high style name conflates two independent choices and doubles the model list.
  • Config in Worker environment variables. A five-kilobyte cap per variable against a config that is already larger than that.
  • Baking config into a per-installation image. Every edit becomes an image build and a rollout.

Pattern ​

Layered configuration resolution. The off-state half of the same design is Null Object and feature toggles resolved once (0018).