53 lines
2.7 KiB
Markdown
53 lines
2.7 KiB
Markdown
 
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# ACP: Session Config Options
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## Metadata
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| Field | Value |
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| Institute | Molodetz Institute — Research & Retrieval Division |
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| Subject | cap-protocol |
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| Document type | Source Dossier |
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| Tier | 1 |
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| Source title | ACP: Session Config Options |
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| Source URL | https://agentclientprotocol.com/protocol/session-config-options |
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| Source publisher / author | Agent Client Protocol project |
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| Source type | standard |
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| Source date (published) | Unknown — not stated |
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| Date researched | 2026-10-25 |
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| Researched by | tai (agent), model: Claude Sonnet 5, on behalf of retoor |
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| Research method | direct page fetch |
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| Confidence | High |
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| Status | Active |
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## Summary
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The ACP mechanism by which an agent advertises per-session selectors (model, mode, reasoning level) and a client changes them. It is the closest existing standard to 'list an agent's models and pick one'.
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## Key findings
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- Each config option has `id`, `name`, optional `description`, optional `category`, `type` (`select` by default, `boolean` only if the client advertised support), `currentValue`, and `options` (flat values or groups, not mixed).
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- Reserved categories: `mode`, `model`, `model_config`, `thought_level`; names starting with `_` are custom; clients MUST handle missing or unknown categories gracefully.
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- The agent MAY return `configOptions` during session setup; the client sets one with `session/set_config_option` (`sessionId`, `configId`, `value`) and the agent MUST answer with the complete list of options and values.
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- The agent announces changes with a `session/update` of `sessionUpdate: config_option_update` carrying the full `configOptions` array.
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- Agents MUST always provide a default for every option; a client that meets an unknown `type` SHOULD ignore that option and the agent keeps its default.
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- Order is significant: higher-priority options first; clients use the order to break ties within a category.
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- If an agent provides `configOptions`, clients SHOULD use them instead of `modes`, which will be removed.
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## Pros / strengths
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Normative (MUST/SHOULD) and small; gives a live, per-agent, per-session model list instead of a static one, with a defined default and ordering.
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## Cons / limitations / caveats
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Only exists for agents that speak ACP; the page does not say how large option lists should be capped; the `model_config` category is separate RFD territory.
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## Relevance to tai
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tai's catalog reads a manifest list or a `--cap-models` probe, both static. For `acp_stdio` agents the live truth is the `model`-category config option from session setup. Recommended as the first discovery source for that binding, with ACP's default-on-unknown rule as the error-resistance model.
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## Changelog
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| Date | Change |
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| 2026-10-25 | Initial dossier created. |
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