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Merged
benbrandt merged 1 commit into from
Sep 22, 2025
Merged

Unstable support for model selection #103

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140 changes: 138 additions & 2 deletions docs/protocol/schema.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -232,6 +232,14 @@ Response from loading an existing session.

<ResponseField name="_meta" type={"object"} >
Extension point for implementations
</ResponseField>
<ResponseField name="models" type={<><span><a href="#sessionmodelstate">SessionModelState</a></span><span> | null</span></>} >
**UNSTABLE**

This capability is not part of the spec yet, and may be removed or changed at any point.

Initial model state if supported by the Agent

</ResponseField>
<ResponseField name="modes" type={<><span><a href="#sessionmodestate">SessionModeState</a></span><span> | null</span></>} >
Initial mode state if supported by the Agent
Expand Down Expand Up @@ -300,6 +308,14 @@ See protocol docs: [Creating a Session](https://agentclientprotocol.com/protocol

<ResponseField name="_meta" type={"object"} >
Extension point for implementations
</ResponseField>
<ResponseField name="models" type={<><span><a href="#sessionmodelstate">SessionModelState</a></span><span> | null</span></>} >
**UNSTABLE**

This capability is not part of the spec yet, and may be removed or changed at any point.

Initial model state if supported by the Agent

</ResponseField>
<ResponseField name="modes" type={<><span><a href="#sessionmodestate">SessionModeState</a></span><span> | null</span></>} >
Initial mode state if supported by the Agent
Expand Down Expand Up @@ -439,6 +455,57 @@ Response to `session/set_mode` method.

<ResponseField name="meta" type={"object"}></ResponseField>

<a id="session-set_model"></a>
### <span class="font-mono">session/set_model</span>

**UNSTABLE**

This capability is not part of the spec yet, and may be removed or changed at any point.

Select a model for a given session.

#### <span class="font-mono">SetSessionModelRequest</span>

**UNSTABLE**

This capability is not part of the spec yet, and may be removed or changed at any point.

Request parameters for setting a session model.

**Type:** Object

**Properties:**

<ResponseField name="_meta" type={"object"}>
Extension point for implementations
</ResponseField>
<ResponseField name="modelId" type={<a href="#modelid">ModelId</a>} required>
The ID of the model to set.
</ResponseField>
<ResponseField
name="sessionId"
type={<a href="#sessionid">SessionId</a>}
required
>
The ID of the session to set the model for.
</ResponseField>

#### <span class="font-mono">SetSessionModelResponse</span>

**UNSTABLE**

This capability is not part of the spec yet, and may be removed or changed at any point.

Response to `session/set_model` method.

**Type:** Object

**Properties:**

<ResponseField name="_meta" type={"object"}>
Extension point for implementations
</ResponseField>

## Client

Defines the interface that ACP-compliant clients must implement.
Expand Down Expand Up @@ -541,7 +608,7 @@ Only available if the client supports the `fs.writeTextFile` capability.

#### <span class="font-mono">WriteTextFileResponse</span>

Response to fs/write_text_file
Response to `fs/write_text_file`

**Type:** Object

Expand Down Expand Up @@ -1093,7 +1160,7 @@ Information about a command.
Input for the command if required
</ResponseField>
<ResponseField name="name" type={"string"} required>
Command name (e.g., "create_plan", "research_codebase").
Command name (e.g., `create_plan`, `research_codebase`).
</ResponseField>

## <span class="font-mono">AvailableCommandInput</span>
Expand Down Expand Up @@ -1622,6 +1689,38 @@ All Agents MUST support this transport.
</Expandable>
</ResponseField>

## <span class="font-mono">ModelId</span>

**UNSTABLE**

This capability is not part of the spec yet, and may be removed or changed at any point.

A unique identifier for a model.

**Type:** `string`

## <span class="font-mono">ModelInfo</span>

**UNSTABLE**

This capability is not part of the spec yet, and may be removed or changed at any point.

Information about a selectable model.

**Type:** Object

**Properties:**

<ResponseField name="_meta" type={"object"}>
Extension point for implementations
</ResponseField>
<ResponseField name="modelId" type={<a href="#modelid">ModelId</a>} required>
Unique identifier for the model.
</ResponseField>
<ResponseField name="name" type={"string"} required>
Human-readable name of the model.
</ResponseField>

## <span class="font-mono">PermissionOption</span>

An option presented to the user when requesting permission.
Expand Down Expand Up @@ -1998,6 +2097,43 @@ The set of modes and the one currently active.
The current mode the Agent is in.
</ResponseField>

## <span class="font-mono">SessionModelState</span>

**UNSTABLE**

This capability is not part of the spec yet, and may be removed or changed at any point.

The set of models and the one currently active.

**Type:** Object

**Properties:**

<ResponseField name="_meta" type={"object"}>
Extension point for implementations
</ResponseField>
<ResponseField
name="availableModels"
type={
<>
<span>
<a href="#modelinfo">ModelInfo</a>
</span>
<span>[]</span>
</>
}
required
>
The set of models that the Agent can use
</ResponseField>
<ResponseField
name="currentModelId"
type={<a href="#modelid">ModelId</a>}
required
>
The current model the Agent is in.
</ResponseField>

## <span class="font-mono">SessionUpdate</span>

Different types of updates that can be sent during session processing.
Expand Down
18 changes: 18 additions & 0 deletions rust/acp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -234,6 +234,19 @@ impl Agent for ClientSideConnection {
)
}

#[cfg(feature = "unstable")]
async fn set_session_model(
&self,
args: SetSessionModelRequest,
) -> Result<SetSessionModelResponse, Error> {
self.conn
.request(
SESSION_SET_MODEL_METHOD_NAME,
Some(ClientRequest::ModelSelectRequest(args)),
)
.await
}

async fn ext_method(&self, args: ExtRequest) -> Result<ExtResponse, Error> {
self.conn
.request(
Expand Down Expand Up @@ -667,6 +680,11 @@ impl<T: Agent> MessageHandler<AgentSide> for T {
let response = self.set_session_mode(args).await?;
Ok(AgentResponse::SetSessionModeResponse(response))
}
#[cfg(feature = "unstable")]
ClientRequest::ModelSelectRequest(args) => {
let response = self.set_session_model(args).await?;
Ok(AgentResponse::ModelSelectResponse(response))
}
ClientRequest::ExtMethodRequest(args) => {
let response = self.ext_method(args).await?;
Ok(AgentResponse::ExtMethodResponse(response))
Expand Down
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