Add model selection support (#93)

This part of ACP is not yet stabilized, so marking as Draft for now

---------

Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>
Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## 0.5.6
 
+- Provide a model selector. We use the "default" model by default, and the user can change it via the client.
 - Make sure writes require permissions when necessary: https://github.com/zed-industries/claude-code-acp/pull/92
 - Add support for appending or overriding the system prompt: https://github.com/zed-industries/claude-code-acp/pull/91
 - Update to @anthropic-ai/claude-agent-sdk@v0.1.15

package-lock.json

@@ -9,7 +9,7 @@
       "version": "0.5.6",
       "license": "Apache-2.0",
       "dependencies": {
-        "@agentclientprotocol/sdk": "0.4.7",
+        "@agentclientprotocol/sdk": "0.4.8",
         "@anthropic-ai/claude-agent-sdk": "0.1.15",
         "@anthropic-ai/claude-code": "2.0.15",
         "@modelcontextprotocol/sdk": "1.20.0",
@@ -40,9 +40,9 @@
       }
     },
     "node_modules/@agentclientprotocol/sdk": {
-      "version": "0.4.7",
-      "resolved": "https://registry.npmjs.org/@agentclientprotocol/sdk/-/sdk-0.4.7.tgz",
-      "integrity": "sha512-tCKNzsHs4TnpCKPjR1eU9qK6LorYs2bxff3bUUREaUgX5JpeH2YpYn0QSNo5qTTMKCKKs55HdjH+/my/ejsZBQ==",
+      "version": "0.4.8",
+      "resolved": "https://registry.npmjs.org/@agentclientprotocol/sdk/-/sdk-0.4.8.tgz",
+      "integrity": "sha512-2hN2CMMWtYVHrUeuapwLu66S2wwOPhq+bLqAryl1cQjKjL5Mzkfq+oxFYFvGdPvBoKpJSxM2pIIQiUH8tGZ3rg==",
       "license": "Apache-2.0",
       "dependencies": {
         "zod": "^3.0.0"

package.json

@@ -51,7 +51,7 @@
   "author": "Zed Industries",
   "license": "Apache-2.0",
   "dependencies": {
-    "@agentclientprotocol/sdk": "0.4.7",
+    "@agentclientprotocol/sdk": "0.4.8",
     "@anthropic-ai/claude-agent-sdk": "0.1.15",
     "@anthropic-ai/claude-code": "2.0.15",
     "@modelcontextprotocol/sdk": "1.20.0",

src/acp-agent.ts

@@ -15,6 +15,9 @@ import {
   ReadTextFileRequest,
   ReadTextFileResponse,
   RequestError,
+  SessionModelState,
+  SetSessionModelRequest,
+  SetSessionModelResponse,
   SetSessionModeRequest,
   SetSessionModeResponse,
   TerminalHandle,
@@ -74,6 +77,8 @@ type ToolUseCache = {
   [key: string]: { type: "tool_use"; id: string; name: string; input: any };
 };
 
+const DEFAULT_MODEL_ID = "default";
+
 // Implement the ACP Agent interface
 export class ClaudeAcpAgent implements Agent {
   sessions: {
@@ -240,8 +245,11 @@ export class ClaudeAcpAgent implements Agent {
       });
     });
 
+    const models = await getAvailableModels(q);
+
     return {
       sessionId,
+      models,
       modes: {
         currentModeId: "default",
         availableModes: [
@@ -388,6 +396,13 @@ export class ClaudeAcpAgent implements Agent {
     await this.sessions[params.sessionId].query.interrupt();
   }
 
+  async setSessionModel(params: SetSessionModelRequest): Promise<SetSessionModelResponse | void> {
+    if (!this.sessions[params.sessionId]) {
+      throw new Error("Session not found");
+    }
+    await this.sessions[params.sessionId].query.setModel(params.modelId);
+  }
+
   async setSessionMode(params: SetSessionModeRequest): Promise<SetSessionModeResponse> {
     if (!this.sessions[params.sessionId]) {
       throw new Error("Session not found");
@@ -428,6 +443,26 @@ export class ClaudeAcpAgent implements Agent {
   }
 }
 
+async function getAvailableModels(query: Query): Promise<SessionModelState> {
+  const models = await query.supportedModels();
+
+  // Query doesn't give us access to the currently selected model, so we default to "default" if it is there,
+  // otherwise we just choose the first model in the list.
+  const currentModel = models.find((model) => model.value === DEFAULT_MODEL_ID) || models[0];
+  await query.setModel(currentModel.value);
+
+  const availableModels = models.map((model) => ({
+    modelId: model.value,
+    name: model.displayName,
+    description: model.description,
+  }));
+
+  return {
+    availableModels,
+    currentModelId: currentModel.value,
+  };
+}
+
 async function getAvailableSlashCommands(query: Query): Promise<AvailableCommand[]> {
   const UNSUPPORTED_COMMANDS = [
     "add-dir",

src/tests/acp-agent.test.ts

@@ -18,7 +18,7 @@ import {
 import { nodeToWebWritable, nodeToWebReadable } from "../utils.js";
 import { markdownEscape, toolInfoFromToolUse, toolUpdateFromToolResult } from "../tools.js";
 import { toAcpNotifications } from "../acp-agent.js";
-import { SDKAssistantMessage } from "@anthropic-ai/claude-agent-sdk";
+import { query, SDKAssistantMessage } from "@anthropic-ai/claude-agent-sdk";
 
 describe.skipIf(!process.env.RUN_INTEGRATION_TESTS)("ACP subprocess integration", () => {
   let child: ReturnType<typeof spawn>;
@@ -780,3 +780,12 @@ describe("escape markdown", () => {
     expect(escaped).toEqual("````\nfor example:\n```markdown\nHello *world*!\n```\n````");
   });
 });
+
+describe("SDK behavior", () => {
+  it("query has a 'default' model", async () => {
+    const q = query({ prompt: "hi" });
+    const models = await q.supportedModels();
+    const defaultModel = models.find((m) => m.value === "default");
+    expect(defaultModel).toBeDefined();
+  });
+});