chore(main): release 0.54.1 (#829 )

🤖 I have created a release *beep* *boop* --- ## [0.54.1](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.54.0...v0.54.1) (2026-06-30) ### Bug Fixes * apply modelOverrides when resolving availableModels allowlist ([#827](https://github.com/agentclientprotocol/claude-agent-acp/issues/827)) ([98c284b](98c284bb87)) --- This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please). Co-authored-by: acp-release-bot[bot] <246668977+acp-release-bot[bot]@users.noreply.github.com>
fix: apply modelOverrides when resolving availableModels allowlist (#827 )
2026-10-27 12:40:32 +00:00 · 2026-06-30 19:03:52 +00:00 · 2026-06-30 19:02:32 +00:00 · 2026-06-30 21:01:39 +02:00 · 2026-06-30 18:40:35 +00:00 · 2026-06-30 18:13:43 +00:00
11 changed files with 1125 additions and 154 deletions
--- a/.release-please-manifest.json
+++ b/.release-please-manifest.json
@@ -1,3 +1,3 @@
 {
-  ".": "0.53.0"
+  ".": "0.54.1"
 }
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,22 @@
 # Changelog

+## [0.54.1](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.54.0...v0.54.1) (2026-06-30)
+
+
+### Bug Fixes
+
+* apply modelOverrides when resolving availableModels allowlist ([#827](https://github.com/agentclientprotocol/claude-agent-acp/issues/827)) ([98c284b](https://github.com/agentclientprotocol/claude-agent-acp/commit/98c284bb871a96710596dfdc2b9ea25d2400f6b2))
+
+## [0.54.0](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.53.0...v0.54.0) (2026-06-30)
+
+
+### Features
+
+* Add Fast mode session config support ([#828](https://github.com/agentclientprotocol/claude-agent-acp/issues/828)) ([fa949a2](https://github.com/agentclientprotocol/claude-agent-acp/commit/fa949a20db0e33f2d63aebeb37e9fea212d8ee95))
+* **deps-dev:** bump prettier from 3.9.1 to 3.9.3 in the minor group ([#821](https://github.com/agentclientprotocol/claude-agent-acp/issues/821)) ([b8df8e0](https://github.com/agentclientprotocol/claude-agent-acp/commit/b8df8e0e5460fd782214f4dde488f7476c80c454))
+* **deps:** bump @anthropic-ai/claude-agent-sdk to 0.3.197 for Sonnet 5 ([#826](https://github.com/agentclientprotocol/claude-agent-acp/issues/826)) ([ef42c46](https://github.com/agentclientprotocol/claude-agent-acp/commit/ef42c46e5aea3bb53f433b9f9dd36a62a9f2df6a))
+* **deps:** bump fast-uri from 3.1.2 to 3.1.3 ([#822](https://github.com/agentclientprotocol/claude-agent-acp/issues/822)) ([64aa130](https://github.com/agentclientprotocol/claude-agent-acp/commit/64aa130c66c299f9835193796ba372b3ed40e7c1))
+
 ## [0.53.0](https://github.com/agentclientprotocol/claude-agent-acp/compare/v0.52.0...v0.53.0) (2026-06-29)


--- a/package-lock.json
+++ b/package-lock.json
@@ -1,32 +1,32 @@
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+      "integrity": "sha512-r4d249KbQ1SFdpeStvob8Ih6aPPIzfqllPVOtvhve6ZcpuVcYo5/7zUWckKpHE7StASX4kTKZTLf0WQm/wPkcg==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
-        "@typescript-eslint/types": "8.62.0",
-        "@typescript-eslint/visitor-keys": "8.62.0"
+        "@typescript-eslint/types": "8.62.1",
+        "@typescript-eslint/visitor-keys": "8.62.1"
      },
      "engines": {
        "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
@@ -1038,9 +1038,9 @@
      }
    },
    "node_modules/@typescript-eslint/tsconfig-utils": {
-      "version": "8.62.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/tsconfig-utils/-/tsconfig-utils-8.62.0.tgz",
-      "integrity": "sha512-y2GAdB6ykaXUvuspbYnizQc4oDDz0Tz/Yc7iWrXf9mx8vm/L/0vLHCe0tS2boG96Zy+DivnVDQ9ZUEWoHqqx1g==",
+      "version": "8.62.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/tsconfig-utils/-/tsconfig-utils-8.62.1.tgz",
+      "integrity": "sha512-xadytJqX9vJVQ2fdQjkcIVigwaOJNWkpjdLt6cEQ+xPnrI1fkp+/jZE/I97k9KUjqtpd25i0HeyZf3T6dutv2g==",
      "dev": true,
      "license": "MIT",
      "engines": {
@@ -1055,15 +1055,15 @@
      }
    },
    "node_modules/@typescript-eslint/type-utils": {
-      "version": "8.62.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/type-utils/-/type-utils-8.62.0.tgz",
-      "integrity": "sha512-+g5O3j0w2ldzC86Pv6fvbO/xhAonbJFIdf/MKQ1d30gndlsVzUOE83ldfSE15Qrl9fhFjK6AovHs5Wpp6vx86w==",
+      "version": "8.62.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/type-utils/-/type-utils-8.62.1.tgz",
+      "integrity": "sha512-aXM5xlqXiTxPibXB93cLAURfT3rlizf7uMXISCXy66Isr/9hISJx3yDsKl0L7lKa51b8JpFuNKby0/O0pEm9jg==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
-        "@typescript-eslint/types": "8.62.0",
-        "@typescript-eslint/typescript-estree": "8.62.0",
-        "@typescript-eslint/utils": "8.62.0",
+        "@typescript-eslint/types": "8.62.1",
+        "@typescript-eslint/typescript-estree": "8.62.1",
+        "@typescript-eslint/utils": "8.62.1",
        "debug": "^4.4.3",
        "ts-api-utils": "^2.5.0"
      },
@@ -1080,9 +1080,9 @@
      }
    },
    "node_modules/@typescript-eslint/types": {
-      "version": "8.62.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/types/-/types-8.62.0.tgz",
-      "integrity": "sha512-KvAclkktORPvM54TgLgA4z9HIV1M8zOgw9ZVNXl9f/8dLYfXYX1wkMXP7qmabpijQRV5bHJLOmoyGQbLMaUYeg==",
+      "version": "8.62.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/types/-/types-8.62.1.tgz",
+      "integrity": "sha512-ooCzJFaf+Hg+uG6fA3NRFGuFjlfNlDhBthbv4ZPU/0elCAFUfnyXUvf/WOpHz/jYwSmvU2GkR2LtyUfy1AxZ1Q==",
      "dev": true,
      "license": "MIT",
      "engines": {
@@ -1094,16 +1094,16 @@
      }
    },
    "node_modules/@typescript-eslint/typescript-estree": {
-      "version": "8.62.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-8.62.0.tgz",
-      "integrity": "sha512-+hVbNxtW64pIcZWDPGbyaKF7vp2IBTVY5ma1blwwksrjdsbdqqEKvJWMGbBofei4F6Dovx1M0RJgoFeNu2279A==",
+      "version": "8.62.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-8.62.1.tgz",
+      "integrity": "sha512-xMcW9oP9u7fAMXYs9A65CVmtLQe2r//oXINHfi8HV+oiqhih17sbLdhXr4540YWlgpDKQdY854OL5ZrdCiQsAA==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
-        "@typescript-eslint/project-service": "8.62.0",
-        "@typescript-eslint/tsconfig-utils": "8.62.0",
-        "@typescript-eslint/types": "8.62.0",
-        "@typescript-eslint/visitor-keys": "8.62.0",
+        "@typescript-eslint/project-service": "8.62.1",
+        "@typescript-eslint/tsconfig-utils": "8.62.1",
+        "@typescript-eslint/types": "8.62.1",
+        "@typescript-eslint/visitor-keys": "8.62.1",
        "debug": "^4.4.3",
        "minimatch": "^10.2.2",
        "semver": "^7.7.3",
@@ -1122,16 +1122,16 @@
      }
    },
    "node_modules/@typescript-eslint/utils": {
-      "version": "8.62.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/utils/-/utils-8.62.0.tgz",
-      "integrity": "sha512-82r66fi9zYwZ+mTq3vKgwjbZ1PVk/DJzrXFLpG6RnBbdvH8TEGVHIs9H4d2drhkOzf0syZuD/OZvvlu6GDbP4g==",
+      "version": "8.62.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/utils/-/utils-8.62.1.tgz",
+      "integrity": "sha512-sHtbPfuKNZCG+ih8SyjjucqRntSVmp8XgL5u6o9mAhiSn8ds5o/M/XdM0abweme2Tln3szOstOrZ9OXitvPh0g==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
        "@eslint-community/eslint-utils": "^4.9.1",
-        "@typescript-eslint/scope-manager": "8.62.0",
-        "@typescript-eslint/types": "8.62.0",
-        "@typescript-eslint/typescript-estree": "8.62.0"
+        "@typescript-eslint/scope-manager": "8.62.1",
+        "@typescript-eslint/types": "8.62.1",
+        "@typescript-eslint/typescript-estree": "8.62.1"
      },
      "engines": {
        "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
@@ -1146,13 +1146,13 @@
      }
    },
    "node_modules/@typescript-eslint/visitor-keys": {
-      "version": "8.62.0",
-      "resolved": "https://registry.npmjs.org/@typescript-eslint/visitor-keys/-/visitor-keys-8.62.0.tgz",
-      "integrity": "sha512-CY3uyFSRbcQv3nnSv8S0+lDftMVz6P963PoRlxrV7ew/Md564g9ut60PYzdLM5qW4jFn93GBF+Soi90ISAN+GQ==",
+      "version": "8.62.1",
+      "resolved": "https://registry.npmjs.org/@typescript-eslint/visitor-keys/-/visitor-keys-8.62.1.tgz",
+      "integrity": "sha512-4g3BLxfdTMy8iZG0MaBkadnlRrCJ74cQiFbyEVMrkwIoqdyaXXQM22cotDvrl4x28wgIZ9rEJRoM+mmhSJpJ1g==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
-        "@typescript-eslint/types": "8.62.0",
+        "@typescript-eslint/types": "8.62.1",
        "eslint-visitor-keys": "^5.0.0"
      },
      "engines": {
@@ -2114,9 +2114,9 @@
      "license": "Unlicense"
    },
    "node_modules/fast-uri": {
-      "version": "3.1.2",
-      "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.2.tgz",
-      "integrity": "sha512-rVjf7ArG3LTk+FS6Yw81V1DLuZl1bRbNrev6Tmd/9RaroeeRRJhAt7jg/6YFxbvAQXUCavSoZhPPj6oOx+5KjQ==",
+      "version": "3.1.3",
+      "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.3.tgz",
+      "integrity": "sha512-i70LwGWUduXqzicKXWshooq+sWL1K3WUU5rKZNG/0i3a1OSoX3HqhH5WbWwTmqWfor4urUakGPiRQcleRZTwOg==",
      "funding": [
        {
          "type": "github",
@@ -3227,9 +3227,9 @@
      }
    },
    "node_modules/prettier": {
-      "version": "3.9.1",
-      "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.9.1.tgz",
-      "integrity": "sha512-ppiDo2CSwexck1eyZUwJHg/N3nf1+6IRCv7W/VJ5vaLnVCmB7+3CdRfMwoCHBBX6xTrREDTksZ4OZl5SSf4zXA==",
+      "version": "3.9.4",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.9.4.tgz",
+      "integrity": "sha512-yWG/o/4oJfo036EKAfK6ACAoDOfHeRHx4tuxkfBZiauURiaSmYwlpOr5LQqKtIkRD2z1PLteme2WoxEnj4tHTg==",
      "dev": true,
      "license": "MIT",
      "bin": {
@@ -3826,16 +3826,16 @@
      }
    },
    "node_modules/vite": {
-      "version": "8.1.0",
-      "resolved": "https://registry.npmjs.org/vite/-/vite-8.1.0.tgz",
-      "integrity": "sha512-BuJcQK/56NQTWDGn4ABea3q4SSBdNPWwNZKTkkUpcMPnLoquSYH8llRtSUIgoL1KSCpHt5eghLShn50mH36y7Q==",
+      "version": "8.1.2",
+      "resolved": "https://registry.npmjs.org/vite/-/vite-8.1.2.tgz",
+      "integrity": "sha512-6YYPbRXTxx6bRXmOn7XdnQAy5DQNHhDgtjhDHI13oe4pY93kkcdGJWxpGwOm++/Wh0QpQhDrpIoVMrmrsI5AGQ==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
        "lightningcss": "^1.32.0",
        "picomatch": "^4.0.4",
-        "postcss": "^8.5.15",
-        "rolldown": "~1.1.2",
+        "postcss": "^8.5.16",
+        "rolldown": "~1.1.3",
        "tinyglobby": "^0.2.17"
      },
      "bin": {
--- a/package.json
+++ b/package.json
@@ -3,7 +3,7 @@
  "publishConfig": {
    "access": "public"
  },
-  "version": "0.53.0",
+  "version": "0.54.1",
  "description": "An ACP-compatible coding agent powered by the Claude Agent SDK (TypeScript)",
  "main": "dist/lib.js",
  "types": "dist/lib.d.ts",
@@ -63,21 +63,21 @@
    "node": ">=22"
  },
  "dependencies": {
-    "@agentclientprotocol/sdk": "1.0.0",
-    "@anthropic-ai/claude-agent-sdk": "0.3.195",
+    "@agentclientprotocol/sdk": "1.1.0",
+    "@anthropic-ai/claude-agent-sdk": "0.3.197",
    "zod": "^3.25.0 || ^4.0.0"
  },
  "devDependencies": {
-    "@anthropic-ai/sdk": "0.106.0",
+    "@anthropic-ai/sdk": "0.108.0",
    "@eslint/js": "10.0.1",
    "@tsconfig/node22": "22.0.5",
    "@types/node": "26.0.1",
-    "@typescript-eslint/eslint-plugin": "8.62.0",
-    "@typescript-eslint/parser": "8.62.0",
+    "@typescript-eslint/eslint-plugin": "8.62.1",
+    "@typescript-eslint/parser": "8.62.1",
    "eslint": "10.6.0",
    "eslint-config-prettier": "10.1.8",
    "globals": "17.7.0",
-    "prettier": "3.9.1",
+    "prettier": "3.9.4",
    "ts-node": "10.9.2",
    "typescript": "6.0.3",
    "vitest": "4.1.9"
--- a/src/acp-agent.ts
+++ b/src/acp-agent.ts
@@ -51,6 +51,7 @@ import {
  AgentInfo,
  CanUseTool,
  deleteSession,
+  FastModeState,
  getSessionInfo,
  getSessionMessages,
  listSessions,
@@ -246,6 +247,10 @@ type Session = {
  /** The currently selected main-thread agent name, or "default" for the
   *  standard Claude Code agent (no `agent` flag applied). */
  currentAgent: string;
+  /** Whether Fast mode is currently enabled for this session. Tracked as the
+   *  user's intent so it persists across model switches; the Fast mode config
+   *  option is only surfaced while the selected model supports it. */
+  fastModeEnabled: boolean;
  abortController: AbortController;
  /** Signal the consumer races `query.next()` against. Aborted by cancel()
   *  (after a grace period) to force the active turn to settle "cancelled" when
@@ -1348,6 +1353,10 @@ export class ClaudeAcpAgent {
          case "system":
            switch (message.subtype) {
              case "init":
+                // A fresh `system`/init (e.g. after reinitialize) can carry an
+                // updated Fast mode state; reconcile it with what we seeded at
+                // session creation.
+                await this.syncFastModeState(message.session_id, session, message.fast_mode_state);
                break;
              case "status": {
                if (message.status === "compacting") {
@@ -1620,6 +1629,14 @@ export class ClaudeAcpAgent {
            // slash-command output forwarding) but their cost is real.
            const isTaskNotification = message.origin?.kind === "task-notification";

+            // Reconcile the Fast mode toggle with the SDK's reported state.
+            // Gated to user-driven turns like every other side effect below; a
+            // background followup's state lands on the next user turn's result.
+            // Runs even when the turn errors or was cancelled.
+            if (!isTaskNotification) {
+              await this.syncFastModeState(params.sessionId, session, message.fast_mode_state);
+            }
+
            // A user-turn result needs an active turn so its stop reason is
            // attributed and the turn settles at idle. Local-only commands carry
            // no user-message echo to promote them, so do it here from the head.
@@ -2383,7 +2400,7 @@ export class ClaudeAcpAgent {
    }

    await this.applySessionMode(params.sessionId, params.modeId);
-    await this.updateConfigOption(params.sessionId, "mode", params.modeId);
+    await this.updateConfigOption(params.sessionId, MODE_CONFIG_ID, params.modeId);
    return {};
  }

@@ -2401,15 +2418,24 @@ export class ClaudeAcpAgent {
    if (session.queryClosed) {
      throw RequestError.internalError(undefined, SESSION_ENDED_MESSAGE);
    }
-    if (typeof params.value !== "string") {
-      throw new Error(`Invalid value for config option ${params.configId}: ${params.value}`);
-    }

    const option = session.configOptions.find((o) => o.id === params.configId);
    if (!option) {
      throw new Error(`Unknown config option: ${params.configId}`);
    }

+    // Fast mode carries a boolean value (for Clients that opted into boolean
+    // config options) or the "on"/"off" select fallback, so it bypasses the
+    // string-only validation the select-style options below rely on.
+    if (params.configId === FAST_MODE_CONFIG_ID) {
+      await this.applyFastMode(session, resolveFastModeEnabled(params));
+      return { configOptions: session.configOptions };
+    }
+
+    if (typeof params.value !== "string") {
+      throw new Error(`Invalid value for config option ${params.configId}: ${params.value}`);
+    }
+
    const allValues =
      "options" in option && Array.isArray(option.options)
        ? option.options.flatMap((o) => ("options" in o ? o.options : [o]))
@@ -2419,7 +2445,7 @@ export class ClaudeAcpAgent {
    // For model options, fall back to resolveModelPreference when the exact
    // value doesn't match.  This lets callers use human-friendly aliases like
    // "opus" or "sonnet" instead of full model IDs like "claude-opus-4-6".
-    if (!validValue && params.configId === "model") {
+    if (!validValue && params.configId === MODEL_CONFIG_ID) {
      const modelInfos: ModelInfo[] = allValues.map((o) => ({
        value: o.value,
        displayName: o.name,
@@ -2439,7 +2465,7 @@ export class ClaudeAcpAgent {
    // model ID rather than the caller-supplied alias.
    const resolvedValue = validValue.value;

-    if (params.configId === "mode") {
+    if (params.configId === MODE_CONFIG_ID) {
      await this.applySessionMode(params.sessionId, resolvedValue);
      await this.client.sessionUpdate({
        sessionId: params.sessionId,
@@ -2448,7 +2474,7 @@ export class ClaudeAcpAgent {
          currentModeId: resolvedValue,
        },
      });
-    } else if (params.configId === "model") {
+    } else if (params.configId === MODEL_CONFIG_ID) {
      await this.sessions[params.sessionId].query.setModel(resolvedValue);
    }
    // Effort SDK sync is handled inside applyConfigOptionValue so that direct
@@ -2706,7 +2732,7 @@ export class ClaudeAcpAgent {
              currentModeId: selectedMode,
            },
          });
-          await this.updateConfigOption(sessionId, "mode", selectedMode);
+          await this.updateConfigOption(sessionId, MODE_CONFIG_ID, selectedMode);

          return {
            behavior: "allow",
@@ -2906,12 +2932,12 @@ export class ClaudeAcpAgent {
    configId: string,
    value: string,
  ): Promise<void> {
-    if (configId === "mode") {
+    if (configId === MODE_CONFIG_ID) {
      session.modes = { ...session.modes, currentModeId: value };
      session.configOptions = session.configOptions.map((o) =>
        o.id === configId && typeof o.currentValue === "string" ? { ...o, currentValue: value } : o,
      );
-    } else if (configId === "model") {
+    } else if (configId === MODEL_CONFIG_ID) {
      // `ModelInfo.supportsAutoMode` is the canonical SDK signal for clamping
      // modes below; its `displayName`/`description` also let us infer the
      // context window for semantic aliases (e.g. `default`) whose ID alone
@@ -2961,7 +2987,7 @@ export class ClaudeAcpAgent {
      }

      // Rebuild config options since effort levels depend on the selected model
-      const effortOpt = session.configOptions.find((o) => o.id === "effort");
+      const effortOpt = session.configOptions.find((o) => o.id === EFFORT_CONFIG_ID);
      const currentEffort =
        typeof effortOpt?.currentValue === "string" ? effortOpt.currentValue : undefined;
      session.configOptions = buildConfigOptions(
@@ -2971,10 +2997,18 @@ export class ClaudeAcpAgent {
        currentEffort,
        session.agents,
        session.currentAgent,
+        {
+          // The toggle follows the newly selected model: it disappears when the
+          // model lacks fast support and reappears (with the retained user
+          // intent) when a supporting model is selected again.
+          supported: newModelInfo?.supportsFastMode ?? false,
+          enabled: session.fastModeEnabled,
+          useBooleanOption: clientSupportsBooleanConfigOptions(this.clientCapabilities),
+        },
      );

      // Sync effort with the SDK if it changed after the model switch
-      const newEffortOpt = session.configOptions.find((o) => o.id === "effort");
+      const newEffortOpt = session.configOptions.find((o) => o.id === EFFORT_CONFIG_ID);
      const newEffort =
        typeof newEffortOpt?.currentValue === "string" ? newEffortOpt.currentValue : undefined;
      if (newEffort !== currentEffort) {
@@ -2998,7 +3032,7 @@ export class ClaudeAcpAgent {
          },
        });
      }
-    } else if (configId === "agent") {
+    } else if (configId === AGENT_CONFIG_ID) {
      // Live agent switch — no subprocess restart needed. Apply the SDK flag
      // first so a rejected control request leaves both `currentAgent` and the
      // config option untouched (no UI/SDK desync). Passing `null` clears the
@@ -3015,7 +3049,7 @@ export class ClaudeAcpAgent {
      session.configOptions = session.configOptions.map((o) =>
        o.id === configId && typeof o.currentValue === "string" ? { ...o, currentValue: value } : o,
      );
-      if (configId === "effort") {
+      if (configId === EFFORT_CONFIG_ID) {
        await session.query.applyFlagSettings({
          effortLevel: toSdkEffortLevel(value),
        });
@@ -3023,6 +3057,77 @@ export class ClaudeAcpAgent {
    }
  }

+  /** Replace the Fast mode option in `session.configOptions` so it reflects
+   *  `enabled` (and the client's current boolean-capability). A no-op when the
+   *  option isn't present, so callers must confirm the current model surfaces
+   *  it first. */
+  private refreshFastModeOption(session: Session, enabled: boolean): void {
+    const refreshed = createFastModeConfigOption(
+      enabled,
+      clientSupportsBooleanConfigOptions(this.clientCapabilities),
+    );
+    session.configOptions = session.configOptions.map((o) =>
+      o.id === FAST_MODE_CONFIG_ID ? refreshed : o,
+    );
+  }
+
+  /** Toggle Fast mode for a session: push the SDK flag, record the user's
+   *  intent, and refresh the Fast mode config option in place. Only reached
+   *  once the option exists (i.e. the current model supports fast mode), so the
+   *  option is guaranteed to be present in `configOptions`. */
+  private async applyFastMode(session: Session, enabled: boolean): Promise<void> {
+    // Apply the SDK flag first so a rejected control request leaves both the
+    // session state and the config option untouched (no UI/SDK desync).
+    await session.query.applyFlagSettings({ fastMode: enabled });
+    session.fastModeEnabled = enabled;
+    this.refreshFastModeOption(session, enabled);
+  }
+
+  /** Reconcile the session's Fast mode toggle with an SDK-reported
+   *  `fast_mode_state` (delivered on `system`/init and on user-turn `result`s).
+   *  The SDK can flip fast mode independently of the user — e.g. back to `on`
+   *  once a rate-limit `cooldown` clears — so we mirror definitive on/off
+   *  changes into the config option and notify the client.
+   *
+   *  Guards, in order:
+   *   - absent state: nothing to reconcile.
+   *   - no Fast mode option: the current model doesn't support fast mode, so the
+   *     reported state reflects capability, not the user's intent. Leave the
+   *     retained setting untouched so it's correct when a supporting model is
+   *     reselected (the source of the earlier intent-clobber bug was mutating it
+   *     here).
+   *   - `cooldown`: a transient suspension of an already-enabled fast mode.
+   *     Leave the toggle as-is rather than flapping it — and never let a stray
+   *     cooldown spuriously enable a toggle the user has off. */
+  private async syncFastModeState(
+    sessionId: string,
+    session: Session,
+    state: FastModeState | undefined,
+  ): Promise<void> {
+    if (state === undefined) {
+      return;
+    }
+    if (!session.configOptions.some((o) => o.id === FAST_MODE_CONFIG_ID)) {
+      return;
+    }
+    if (state === "cooldown") {
+      return;
+    }
+    const enabled = state === "on";
+    if (enabled === session.fastModeEnabled) {
+      return;
+    }
+    session.fastModeEnabled = enabled;
+    this.refreshFastModeOption(session, enabled);
+    await this.client.sessionUpdate({
+      sessionId,
+      update: {
+        sessionUpdate: "config_option_update",
+        configOptions: session.configOptions,
+      },
+    });
+  }
+
  private async getOrCreateSession(params: {
    sessionId: string;
    cwd: string;
@@ -3274,7 +3379,7 @@ export class ClaudeAcpAgent {
                      currentModeId: "plan",
                    },
                  });
-                  await this.updateConfigOption(sessionId, "mode", "plan");
+                  await this.updateConfigOption(sessionId, MODE_CONFIG_ID, "plan");
                },
              }),
            ],
@@ -3381,8 +3486,13 @@ export class ClaudeAcpAgent {
    // configOptions, the current-model resolver, and the stored modelInfos
    // consistent with what the user configured.
    const settingsAvailableModels = settingsManager.getSettings().availableModels;
+    const settingsModelOverrides = settingsManager.getSettings().modelOverrides;
    const allowedModels = Array.isArray(settingsAvailableModels)
-      ? applyAvailableModelsAllowlist(initializationResult.models, settingsAvailableModels)
+      ? applyAvailableModelsAllowlist(
+          initializationResult.models,
+          settingsAvailableModels,
+          settingsModelOverrides,
+        )
      : initializationResult.models;

    const models = await getAvailableModels(
@@ -3445,6 +3555,19 @@ export class ClaudeAcpAgent {
        ? requestedAgent
        : DEFAULT_AGENT_ID;

+    // Seed Fast mode from the SDK's reported state so the UI reflects reality
+    // (the CLI may start a session with fast mode already on, or force it off
+    // when `fastModePerSessionOptIn` is set). The toggle is only surfaced while
+    // the resolved model advertises `supportsFastMode`.
+    const fastModeEnabled =
+      initializationResult.fast_mode_state !== undefined &&
+      fastModeStateEnabled(initializationResult.fast_mode_state);
+    const fastMode: FastModeOptionState = {
+      supported: currentModelInfo?.supportsFastMode ?? false,
+      enabled: fastModeEnabled,
+      useBooleanOption: clientSupportsBooleanConfigOptions(this.clientCapabilities),
+    };
+
    const configOptions = buildConfigOptions(
      modes,
      models,
@@ -3452,10 +3575,11 @@ export class ClaudeAcpAgent {
      settingsManager.getSettings().effortLevel,
      agents,
      currentAgent,
+      fastMode,
    );

    // Apply the initial effort level to the SDK so it matches the UI default
-    const initialEffort = configOptions.find((o) => o.id === "effort");
+    const initialEffort = configOptions.find((o) => o.id === EFFORT_CONFIG_ID);
    if (
      initialEffort &&
      typeof initialEffort.currentValue === "string" &&
@@ -3484,6 +3608,7 @@ export class ClaudeAcpAgent {
      configOptions,
      agents,
      currentAgent,
+      fastModeEnabled,
      abortController,
      emitRawSDKMessages: sessionMeta?.claudeCode?.emitRawSDKMessages ?? false,
      contextWindowSize:
@@ -3704,6 +3829,96 @@ export async function discoverCustomAgents(q: Query): Promise<AgentInfo[]> {
  }
 }

+/** Stable ids for the session config options surfaced via `configOptions`.
+ *  Centralized so the option declarations in `buildConfigOptions` and the
+ *  handlers in `setSessionConfigOption`/`applyConfigOptionValue` reference the
+ *  same identifiers and can't drift apart. */
+export const MODE_CONFIG_ID = "mode";
+export const MODEL_CONFIG_ID = "model";
+export const EFFORT_CONFIG_ID = "effort";
+export const AGENT_CONFIG_ID = "agent";
+export const FAST_MODE_CONFIG_ID = "fast";
+
+/** Select-fallback values used when the client has not opted into boolean
+ *  config options (see {@link createFastModeConfigOption}). */
+export const FAST_MODE_ON = "on";
+export const FAST_MODE_OFF = "off";
+const FAST_MODE_DESCRIPTION = "Faster responses on supported models";
+
+/** Map the SDK's tri-state `fast_mode_state` onto the boolean config toggle.
+ *  `cooldown` (fast mode temporarily suspended after a rate limit, per the SDK
+ *  docs) keeps the toggle on so it reflects the user's intent — only an
+ *  explicit `off` clears it. */
+export function fastModeStateEnabled(state: FastModeState): boolean {
+  return state !== "off";
+}
+
+/** Whether the Client advertised support for boolean session config options
+ *  (`session.configOptions.boolean`). Agents MUST only send `type: "boolean"`
+ *  config options to Clients that opt in; otherwise we fall back to a `select`.
+ *  See https://agentclientprotocol.com/rfds/boolean-config-option. */
+export function clientSupportsBooleanConfigOptions(
+  clientCapabilities?: ClientCapabilities | null,
+): boolean {
+  return clientCapabilities?.session?.configOptions?.boolean != null;
+}
+
+/** Build the Fast mode config option. When the Client supports boolean config
+ *  options we expose a native `type: "boolean"` toggle; otherwise we degrade to
+ *  a two-value `select` ("on"/"off") so older Clients still get a usable
+ *  control. */
+export function createFastModeConfigOption(
+  enabled: boolean,
+  useBooleanOption: boolean,
+): SessionConfigOption {
+  const base = {
+    id: FAST_MODE_CONFIG_ID,
+    name: "Fast mode",
+    description: FAST_MODE_DESCRIPTION,
+    category: "model_config",
+  } as const;
+
+  if (useBooleanOption) {
+    return { ...base, type: "boolean", currentValue: enabled };
+  }
+
+  return {
+    ...base,
+    type: "select",
+    currentValue: enabled ? FAST_MODE_ON : FAST_MODE_OFF,
+    options: [
+      { value: FAST_MODE_ON, name: "On" },
+      { value: FAST_MODE_OFF, name: "Off" },
+    ],
+  };
+}
+
+/** Resolve the requested Fast mode value from a `session/set_config_option`
+ *  request. Accepts a native boolean (boolean-capable Clients) or the
+ *  "on"/"off" select-fallback strings. */
+export function resolveFastModeEnabled(params: SetSessionConfigOptionRequest): boolean {
+  const value = params.value;
+  if (typeof value === "boolean") {
+    return value;
+  }
+  if (value === FAST_MODE_ON) {
+    return true;
+  }
+  if (value === FAST_MODE_OFF) {
+    return false;
+  }
+  throw new Error(`Invalid value for config option ${FAST_MODE_CONFIG_ID}: ${value}`);
+}
+
+/** Per-model Fast mode state threaded into {@link buildConfigOptions}. The
+ *  option is only surfaced when the current model `supported`s fast mode. */
+export type FastModeOptionState = {
+  supported: boolean;
+  enabled: boolean;
+  /** Whether the Client opted into boolean config options. */
+  useBooleanOption: boolean;
+};
+
 export function buildConfigOptions(
  modes: SessionModeState,
  models: SessionModelState,
@@ -3711,10 +3926,11 @@ export function buildConfigOptions(
  currentEffortLevel?: string,
  agents: AgentInfo[] = [],
  currentAgent: string = DEFAULT_AGENT_ID,
+  fastMode?: FastModeOptionState,
 ): SessionConfigOption[] {
  const options: SessionConfigOption[] = [
    {
-      id: "mode",
+      id: MODE_CONFIG_ID,
      name: "Mode",
      description: "Session permission mode",
      category: "mode",
@@ -3727,7 +3943,7 @@ export function buildConfigOptions(
      })),
    },
    {
-      id: "model",
+      id: MODEL_CONFIG_ID,
      name: "Model",
      description: "AI model to use",
      category: "model",
@@ -3764,7 +3980,7 @@ export function buildConfigOptions(
      currentEffortLevel && includes(currentEffortLevel) ? currentEffortLevel : "default";

    options.push({
-      id: "effort",
+      id: EFFORT_CONFIG_ID,
      name: "Effort",
      description: "Available effort levels for this model",
      category: "thought_level",
@@ -3774,13 +3990,20 @@ export function buildConfigOptions(
    });
  }

+  // Surface the Fast mode toggle only when the current model supports it. The
+  // option renders as a native boolean toggle for Clients that opted in, and a
+  // two-value select otherwise.
+  if (fastMode?.supported) {
+    options.push(createFastModeConfigOption(fastMode.enabled, fastMode.useBooleanOption));
+  }
+
  // Only surface the Agent picker when there's a real choice — i.e. the user
  // has configured at least one custom agent (built-ins are filtered out in
  // discoverCustomAgents). With none configured, "Default" would be the only
  // entry, so we omit the option entirely.
  if (agents.length > 0) {
    options.push({
-      id: "agent",
+      id: AGENT_CONFIG_ID,
      name: "Agent",
      description: "Main-thread agent persona",
      type: "select",
@@ -3803,14 +4026,17 @@ export function buildConfigOptions(
 // but the SDK model list uses IDs like "claude-opus-4-6-1m".
 const MODEL_CONTEXT_HINT_PATTERN = /\[(\d+m)\]$/i;

-// Captures a model family version such as `4-6` or `4.7` so we can keep
-// `claude-opus-4-6` from being copied onto the SDK's `opus` alias when that
-// alias currently resolves to a different family version (e.g. Opus 4.7).
-const MODEL_FAMILY_VERSION_PATTERN = /\b(\d+)[-.](\d+)\b/;
+// Captures a model family version: `4-6`/`4.7` for dated generations, or a
+// bare `5` for single-number ones like "Sonnet 5". Used to keep a pinned
+// `claude-opus-4-6` from matching the `opus` alias once it points at 4.7.
+const MODEL_FAMILY_VERSION_PATTERN = /\b(\d+)(?:[-.](\d+))?\b/;

 function extractModelFamilyVersion(s: string): string | null {
-  const match = s.match(MODEL_FAMILY_VERSION_PATTERN);
-  return match ? `${match[1]}.${match[2]}` : null;
+  // Strip "[1m]"-style context hints first — that digit is context window
+  // size, not a model generation version.
+  const match = s.replace(/\[\d+m\]/gi, "").match(MODEL_FAMILY_VERSION_PATTERN);
+  if (!match) return null;
+  return match[2] ? `${match[1]}.${match[2]}` : match[1];
 }

 function modelVersionsCompatible(preference: string, candidate: ModelInfo): boolean {
@@ -3856,7 +4082,7 @@ function scoreModelMatch(model: ModelInfo, tokens: string[], contextHint?: strin
  return score;
 }

-function resolveModelPreference(models: ModelInfo[], preference: string): ModelInfo | null {
+export function resolveModelPreference(models: ModelInfo[], preference: string): ModelInfo | null {
  const trimmed = preference.trim();
  if (!trimmed) return null;

@@ -3871,6 +4097,18 @@ function resolveModelPreference(models: ModelInfo[], preference: string): ModelI
  );
  if (directMatch) return directMatch;

+  // Exact match on the alias's canonical resolved id (e.g. a pinned
+  // "claude-sonnet-5" against the "sonnet" row's `resolvedModel`). SDK-
+  // reported and unambiguous, so it's tried before the fuzzier tiers below.
+  // "default" is skipped first since it shares a resolvedModel with
+  // whichever alias the CLI currently recommends — a specific pin should
+  // land on that named alias, not "default".
+  const resolvedMatch =
+    models.find(
+      (model) => model.value !== "default" && model.resolvedModel?.toLowerCase() === lower,
+    ) ?? models.find((model) => model.resolvedModel?.toLowerCase() === lower);
+  if (resolvedMatch) return resolvedMatch;
+
  // Substring match
  const includesMatch = models.find((model) => {
    if (!modelVersionsCompatible(trimmed, model)) return false;
@@ -3930,7 +4168,11 @@ function resolveSettingsModel(
 * - The Default option is unaffected by `availableModels` — it always remains
 *   available, even when the allowlist is `[]`.
 */
-function applyAvailableModelsAllowlist(sdkModels: ModelInfo[], allowlist: string[]): ModelInfo[] {
+export function applyAvailableModelsAllowlist(
+  sdkModels: ModelInfo[],
+  allowlist: string[],
+  settingsModelOverrides?: Record<string, string>,
+): ModelInfo[] {
  // Default is always preserved per the docs. Synthesize one if the SDK
  // didn't surface it so downstream code (e.g. `getAvailableModels` picking
  // `models[0]` as a fallback) still has something to work with.
@@ -3944,17 +4186,28 @@ function applyAvailableModelsAllowlist(sdkModels: ModelInfo[], allowlist: string

  const sdkModelsWithoutDefault = sdkModels.filter((m) => m.value !== "default");

+  // Bedrock/Vertex deployments enforce short aliases (e.g. "claude-opus-4-6")
+  // in availableModels but require provider-specific IDs at the API. We still
+  // resolve `sdkMatch` against the alias (`trimmed`) — that's what the
+  // matching heuristics above are built for, and override targets (ARNs,
+  // opaque provider IDs) often won't textually resemble anything in
+  // `sdkModelsWithoutDefault`. Only the entry's surfaced `value` becomes the
+  // override target, so it's what `setModel` ends up passing to the API.
  for (const entry of allowlist) {
    const trimmed = entry.trim();
    if (!trimmed || seen.has(trimmed)) continue;

+    const overridden = settingsModelOverrides?.[trimmed];
+    const effective = overridden ?? trimmed;
+    if (seen.has(effective)) continue;
+
    const sdkMatch = resolveModelPreference(sdkModelsWithoutDefault, trimmed);
    if (sdkMatch) {
-      result.push({ ...sdkMatch, value: trimmed });
+      result.push({ ...sdkMatch, value: effective });
    } else {
-      result.push({ value: trimmed, displayName: trimmed, description: "" });
+      result.push({ value: effective, displayName: trimmed, description: "" });
    }
-    seen.add(trimmed);
+    seen.add(effective);
  }

  // The custom model option (ANTHROPIC_CUSTOM_MODEL_OPTION) is exempt from the
--- a/src/tests/acp-agent-settings.test.ts
+++ b/src/tests/acp-agent-settings.test.ts
@@ -811,6 +811,55 @@ describe("ClaudeAcpAgent settings", () => {
        }
      }
    });
+
+    it("maps allowlist aliases through modelOverrides to provider IDs", async () => {
+      // Bedrock/Vertex deployments enforce short aliases in availableModels
+      // but require provider-specific IDs at the API. Without applying
+      // modelOverrides during allowlist resolution, the alias is surfaced as
+      // the model value and passed verbatim to setModel, which the provider
+      // API rejects with a 400 "invalid model identifier".
+      await fs.promises.writeFile(
+        path.join(tempDir, "settings.json"),
+        JSON.stringify({
+          availableModels: ["claude-opus-4-6", "claude-sonnet-4-6"],
+          model: "claude-opus-4-6",
+          modelOverrides: {
+            "claude-opus-4-6": "global.anthropic.claude-opus-4-6-v1[1m]",
+            "claude-sonnet-4-6": "global.anthropic.claude-sonnet-4-6[1m]",
+          },
+        }),
+      );
+
+      const projectDir = path.join(tempDir, "project");
+      await fs.promises.mkdir(projectDir, { recursive: true });
+
+      const { setModelSpy } = mockQueryWithModels([
+        { value: "default", displayName: "Default", description: "Default model" },
+        { value: "opus", displayName: "Opus", description: "Claude Opus 4.6" },
+        { value: "sonnet", displayName: "Sonnet", description: "Claude Sonnet 4.6" },
+      ]);
+
+      const { ClaudeAcpAgent } = await import("../acp-agent.js");
+      const agent: ClaudeAcpAgentType = new ClaudeAcpAgent(createMockClient());
+
+      const response = await (agent as any).createSession({
+        cwd: projectDir,
+        mcpServers: [],
+        _meta: { disableBuiltInTools: true },
+      });
+
+      const modelOption = response.configOptions.find((o: any) => o.id === "model");
+      expect(modelOption.options.map((o: any) => o.value)).toEqual([
+        "default",
+        "global.anthropic.claude-opus-4-6-v1[1m]",
+        "global.anthropic.claude-sonnet-4-6[1m]",
+      ]);
+      // The allowlist synthesized the overridden ID (the SDK only surfaced the
+      // `opus` alias), so the adapter syncs the provider ID via setModel — never
+      // the raw alias that Bedrock would reject.
+      expect(setModelSpy).toHaveBeenCalledWith("global.anthropic.claude-opus-4-6-v1[1m]");
+      expect(modelOption.currentValue).toBe("global.anthropic.claude-opus-4-6-v1[1m]");
+    });
  });

  it("resolves model aliases like opus[1m] to the correct model", async () => {
--- a/src/tests/acp-agent.test.ts
+++ b/src/tests/acp-agent.test.ts
@@ -37,6 +37,7 @@ import {
  streamEventToAcpNotifications,
  messageIdForGrouping,
  buildConfigOptions,
+  createFastModeConfigOption,
  discoverCustomAgents,
  runPromptWithCancellation,
  type AcpClient,
@@ -1810,6 +1811,7 @@ describe("permission request cancellation", () => {
      configOptions: [],
      agents: [],
      currentAgent: "default",
+      fastModeEnabled: false,
      abortController: new AbortController(),
      emitRawSDKMessages: false,
      contextWindowSize: 200000,
@@ -2267,6 +2269,77 @@ describe("stop reason propagation", () => {
    expect(response.usage?.outputTokens).toBe(promptResult.usage.output_tokens);
  });

+  it("only reconciles Fast mode from user-driven results, not task-notification followups", async () => {
+    const updates: any[] = [];
+    const mockClient = {
+      sessionUpdate: async (n: any) => {
+        updates.push(n);
+      },
+    } as unknown as AcpClient;
+    const agent = new ClaudeAcpAgent(mockClient, { log: () => {}, error: () => {} });
+    (agent as any).clientCapabilities = { session: { configOptions: { boolean: {} } } };
+
+    const input = new Pushable<any>();
+
+    // A background followup reports fast_mode_state="on". It must NOT flip the
+    // user's toggle or emit a config_option_update (every other side effect in
+    // the result handler is likewise gated behind !isTaskNotification).
+    const backgroundTaskResult = {
+      ...createResultMessage({ subtype: "success", stop_reason: null, is_error: false }),
+      origin: { kind: "task-notification" },
+      fast_mode_state: "on",
+    };
+
+    // The user prompt's own result reports the same state — this one IS a user
+    // turn, so it reconciles and notifies.
+    const promptResult = {
+      ...createResultMessage({ subtype: "success", stop_reason: null, is_error: false }),
+      fast_mode_state: "on",
+    };
+
+    async function* messageGenerator() {
+      yield { type: "system", subtype: "init", session_id: "test-session" };
+      yield backgroundTaskResult;
+
+      const iter = input[Symbol.asyncIterator]();
+      const { value: userMessage } = await iter.next();
+      yield {
+        type: "user",
+        message: userMessage.message,
+        parent_tool_use_id: null,
+        uuid: userMessage.uuid,
+        session_id: "test-session",
+        isReplay: true,
+      };
+
+      yield promptResult;
+      yield { type: "system", subtype: "session_state_changed", state: "idle" };
+    }
+
+    agent.sessions["test-session"] = mockSessionState({
+      query: wrapQuery(messageGenerator()),
+      input,
+      fastModeEnabled: false,
+      configOptions: [createFastModeConfigOption(false, true)],
+    });
+
+    await agent.prompt({
+      sessionId: "test-session",
+      prompt: [{ type: "text", text: "test" }],
+    });
+
+    // The user-turn result flipped the toggle and emitted exactly one
+    // config_option_update; the background result contributed none.
+    expect((agent.sessions["test-session"] as any).fastModeEnabled).toBe(true);
+    const configUpdates = updates.filter(
+      (n: any) => n.update?.sessionUpdate === "config_option_update",
+    );
+    expect(configUpdates).toHaveLength(1);
+    expect(configUpdates[0].update.configOptions).toContainEqual(
+      createFastModeConfigOption(true, true),
+    );
+  });
+
  it("does not fold a task-notification result's tokens into an already-active turn's usage", async () => {
    const agent = createMockAgent();

@@ -2713,6 +2786,7 @@ describe("session/close", () => {
      configOptions: [],
      agents: [],
      currentAgent: "default",
+      fastModeEnabled: false,
      abortController: new AbortController(),
      emitRawSDKMessages: false,
      contextWindowSize: 200000,
@@ -2799,6 +2873,7 @@ describe("session/delete", () => {
      configOptions: [],
      agents: [],
      currentAgent: "default",
+      fastModeEnabled: false,
      abortController: new AbortController(),
      emitRawSDKMessages: false,
      contextWindowSize: 200000,
@@ -2902,6 +2977,7 @@ describe("getOrCreateSession param change detection", () => {
      configOptions: [],
      agents: [],
      currentAgent: "default",
+      fastModeEnabled: false,
      abortController: new AbortController(),
      emitRawSDKMessages: false,
      contextWindowSize: 200000,
@@ -5117,6 +5193,7 @@ describe("post-error recovery", () => {
      configOptions: [],
      agents: [],
      currentAgent: "default",
+      fastModeEnabled: false,
      abortController: new AbortController(),
      emitRawSDKMessages: false,
      contextWindowSize: 200000,
@@ -5688,6 +5765,7 @@ describe("session/cancel wedge recovery (issue #680)", () => {
      configOptions: [],
      agents: [],
      currentAgent: "default",
+      fastModeEnabled: false,
      abortController: new AbortController(),
      emitRawSDKMessages: false,
      contextWindowSize: 200000,
@@ -6142,6 +6220,7 @@ describe("agent selection config option", () => {
        configOptions: buildConfigOptions(baseModes, baseModels, [], undefined, agents, "default"),
        agents,
        currentAgent: "default",
+        fastModeEnabled: false,
        abortController: new AbortController(),
        emitRawSDKMessages: false,
        contextWindowSize: 200000,
--- a/src/tests/fast-mode-config.test.ts
+++ b/src/tests/fast-mode-config.test.ts
@@ -0,0 +1,341 @@
+import { describe, it, expect, vi } from "vitest";
+import type { ClientCapabilities, SessionNotification } from "@agentclientprotocol/sdk";
+import type { ModelInfo } from "@anthropic-ai/claude-agent-sdk";
+import {
+  buildConfigOptions,
+  clientSupportsBooleanConfigOptions,
+  createFastModeConfigOption,
+  fastModeStateEnabled,
+  resolveFastModeEnabled,
+  FAST_MODE_CONFIG_ID,
+  FAST_MODE_ON,
+  FAST_MODE_OFF,
+  ClaudeAcpAgent,
+  type AcpClient,
+} from "../acp-agent.js";
+
+const MODES = {
+  currentModeId: "default",
+  availableModes: [{ id: "default", name: "Default", description: "Standard behavior" }],
+};
+
+const MODELS = {
+  currentModelId: "claude-opus-4-8",
+  availableModels: [
+    { modelId: "claude-opus-4-8", name: "Claude Opus", description: "Most capable" },
+  ],
+};
+
+const MODEL_INFOS: ModelInfo[] = [
+  { value: "claude-opus-4-8", displayName: "Claude Opus", description: "Most capable" },
+];
+
+describe("createFastModeConfigOption", () => {
+  it("produces a native boolean toggle when the client opted in", () => {
+    expect(createFastModeConfigOption(true, true)).toEqual({
+      id: FAST_MODE_CONFIG_ID,
+      name: "Fast mode",
+      description: expect.any(String),
+      category: "model_config",
+      type: "boolean",
+      currentValue: true,
+    });
+  });
+
+  it("falls back to an on/off select when the client did not opt in", () => {
+    const option = createFastModeConfigOption(false, false);
+    expect(option).toMatchObject({
+      id: FAST_MODE_CONFIG_ID,
+      type: "select",
+      category: "model_config",
+      currentValue: FAST_MODE_OFF,
+      options: [
+        { value: FAST_MODE_ON, name: "On" },
+        { value: FAST_MODE_OFF, name: "Off" },
+      ],
+    });
+    expect(option).not.toHaveProperty("currentValue", true);
+  });
+});
+
+describe("clientSupportsBooleanConfigOptions", () => {
+  it("is true only when session.configOptions.boolean is present", () => {
+    expect(
+      clientSupportsBooleanConfigOptions({ session: { configOptions: { boolean: {} } } }),
+    ).toBe(true);
+  });
+
+  it("is false when the capability is omitted or null at any level", () => {
+    expect(clientSupportsBooleanConfigOptions(undefined)).toBe(false);
+    expect(clientSupportsBooleanConfigOptions(null)).toBe(false);
+    expect(clientSupportsBooleanConfigOptions({})).toBe(false);
+    expect(clientSupportsBooleanConfigOptions({ session: { configOptions: {} } })).toBe(false);
+    expect(
+      clientSupportsBooleanConfigOptions({ session: { configOptions: { boolean: null } } }),
+    ).toBe(false);
+  });
+});
+
+describe("resolveFastModeEnabled", () => {
+  const base = { sessionId: "s", configId: FAST_MODE_CONFIG_ID };
+
+  it("accepts native boolean values", () => {
+    expect(resolveFastModeEnabled({ ...base, type: "boolean", value: true })).toBe(true);
+    expect(resolveFastModeEnabled({ ...base, type: "boolean", value: false })).toBe(false);
+  });
+
+  it("accepts the on/off select fallback", () => {
+    expect(resolveFastModeEnabled({ ...base, value: FAST_MODE_ON })).toBe(true);
+    expect(resolveFastModeEnabled({ ...base, value: FAST_MODE_OFF })).toBe(false);
+  });
+
+  it("rejects any other value", () => {
+    expect(() => resolveFastModeEnabled({ ...base, value: "maybe" })).toThrow(
+      /Invalid value for config option fast/,
+    );
+  });
+});
+
+describe("fastModeStateEnabled", () => {
+  it("treats cooldown as on (the user's intent persists through rate-limit cooldown)", () => {
+    expect(fastModeStateEnabled("on")).toBe(true);
+    expect(fastModeStateEnabled("cooldown")).toBe(true);
+    expect(fastModeStateEnabled("off")).toBe(false);
+  });
+});
+
+describe("buildConfigOptions Fast mode", () => {
+  it("omits the Fast mode option when the model does not support it", () => {
+    const options = buildConfigOptions(MODES, MODELS, MODEL_INFOS, undefined, [], "default", {
+      supported: false,
+      enabled: false,
+      useBooleanOption: true,
+    });
+    expect(options.find((o) => o.id === FAST_MODE_CONFIG_ID)).toBeUndefined();
+  });
+
+  it("omits the Fast mode option when no fast mode state is provided", () => {
+    const options = buildConfigOptions(MODES, MODELS, MODEL_INFOS, undefined, [], "default");
+    expect(options.find((o) => o.id === FAST_MODE_CONFIG_ID)).toBeUndefined();
+  });
+
+  it("surfaces a boolean toggle when supported and the client opted in", () => {
+    const options = buildConfigOptions(MODES, MODELS, MODEL_INFOS, undefined, [], "default", {
+      supported: true,
+      enabled: true,
+      useBooleanOption: true,
+    });
+    expect(options).toContainEqual(createFastModeConfigOption(true, true));
+  });
+
+  it("surfaces a select fallback when supported but the client did not opt in", () => {
+    const options = buildConfigOptions(MODES, MODELS, MODEL_INFOS, undefined, [], "default", {
+      supported: true,
+      enabled: false,
+      useBooleanOption: false,
+    });
+    expect(options).toContainEqual(createFastModeConfigOption(false, false));
+  });
+});
+
+describe("setSessionConfigOption Fast mode toggle", () => {
+  const SESSION_ID = "fast-session";
+
+  function setup(opts: { useBooleanOption: boolean }) {
+    const sessionUpdates: SessionNotification[] = [];
+    const client = {
+      sessionUpdate: async (n: SessionNotification) => {
+        sessionUpdates.push(n);
+      },
+      requestPermission: async () => ({ outcome: { outcome: "cancelled" } }),
+      readTextFile: async () => ({ content: "" }),
+      writeTextFile: async () => ({}),
+    } as unknown as AcpClient;
+
+    const agent = new ClaudeAcpAgent(client);
+    const clientCapabilities: ClientCapabilities = opts.useBooleanOption
+      ? { session: { configOptions: { boolean: {} } } }
+      : {};
+    (agent as unknown as { clientCapabilities: ClientCapabilities }).clientCapabilities =
+      clientCapabilities;
+
+    const applyFlagSettings = vi.fn();
+    (agent as unknown as { sessions: Record<string, unknown> }).sessions[SESSION_ID] = {
+      query: { applyFlagSettings },
+      fastModeEnabled: false,
+      configOptions: [createFastModeConfigOption(false, opts.useBooleanOption)],
+    };
+
+    return { agent, applyFlagSettings, sessionUpdates };
+  }
+
+  it("toggles Fast mode on/off through a boolean value", async () => {
+    const { agent, applyFlagSettings } = setup({ useBooleanOption: true });
+
+    const onResponse = await agent.setSessionConfigOption({
+      sessionId: SESSION_ID,
+      configId: FAST_MODE_CONFIG_ID,
+      type: "boolean",
+      value: true,
+    });
+    expect(applyFlagSettings).toHaveBeenCalledWith({ fastMode: true });
+    expect(onResponse.configOptions).toContainEqual(createFastModeConfigOption(true, true));
+    expect(
+      (agent as unknown as { sessions: Record<string, { fastModeEnabled: boolean }> }).sessions[
+        SESSION_ID
+      ].fastModeEnabled,
+    ).toBe(true);
+
+    const offResponse = await agent.setSessionConfigOption({
+      sessionId: SESSION_ID,
+      configId: FAST_MODE_CONFIG_ID,
+      type: "boolean",
+      value: false,
+    });
+    expect(applyFlagSettings).toHaveBeenLastCalledWith({ fastMode: false });
+    expect(offResponse.configOptions).toContainEqual(createFastModeConfigOption(false, true));
+  });
+
+  it("toggles Fast mode through the on/off select fallback", async () => {
+    const { agent, applyFlagSettings } = setup({ useBooleanOption: false });
+
+    const response = await agent.setSessionConfigOption({
+      sessionId: SESSION_ID,
+      configId: FAST_MODE_CONFIG_ID,
+      value: FAST_MODE_ON,
+    });
+    expect(applyFlagSettings).toHaveBeenCalledWith({ fastMode: true });
+    expect(response.configOptions).toContainEqual(createFastModeConfigOption(true, false));
+  });
+
+  it("does not change session state when the SDK rejects the flag", async () => {
+    const { agent, applyFlagSettings } = setup({ useBooleanOption: true });
+    applyFlagSettings.mockRejectedValueOnce(new Error("nope"));
+
+    await expect(
+      agent.setSessionConfigOption({
+        sessionId: SESSION_ID,
+        configId: FAST_MODE_CONFIG_ID,
+        type: "boolean",
+        value: true,
+      }),
+    ).rejects.toThrow("nope");
+
+    const session = (agent as unknown as { sessions: Record<string, { fastModeEnabled: boolean }> })
+      .sessions[SESSION_ID];
+    expect(session.fastModeEnabled).toBe(false);
+  });
+});
+
+describe("syncFastModeState (SDK-driven state changes)", () => {
+  const SESSION_ID = "fast-session";
+
+  function setup(opts: { fastModeEnabled: boolean; withOption: boolean }) {
+    const sessionUpdates: SessionNotification[] = [];
+    const client = {
+      sessionUpdate: async (n: SessionNotification) => {
+        sessionUpdates.push(n);
+      },
+      requestPermission: async () => ({ outcome: { outcome: "cancelled" } }),
+      readTextFile: async () => ({ content: "" }),
+      writeTextFile: async () => ({}),
+    } as unknown as AcpClient;
+
+    const agent = new ClaudeAcpAgent(client);
+    (agent as unknown as { clientCapabilities: ClientCapabilities }).clientCapabilities = {
+      session: { configOptions: { boolean: {} } },
+    };
+
+    const session = {
+      query: {},
+      fastModeEnabled: opts.fastModeEnabled,
+      configOptions: opts.withOption
+        ? [createFastModeConfigOption(opts.fastModeEnabled, true)]
+        : [],
+    };
+    (agent as unknown as { sessions: Record<string, unknown> }).sessions[SESSION_ID] = session;
+
+    const sync = (
+      agent as unknown as {
+        syncFastModeState: (
+          sessionId: string,
+          session: unknown,
+          state: string | undefined,
+        ) => Promise<void>;
+      }
+    ).syncFastModeState.bind(agent);
+
+    return { sync, session, sessionUpdates };
+  }
+
+  it("emits a config_option_update when the SDK reports a new state", async () => {
+    const { sync, session, sessionUpdates } = setup({ fastModeEnabled: false, withOption: true });
+
+    await sync(SESSION_ID, session, "on");
+
+    expect(session.fastModeEnabled).toBe(true);
+    expect(session.configOptions).toContainEqual(createFastModeConfigOption(true, true));
+    expect(sessionUpdates).toHaveLength(1);
+    expect(sessionUpdates[0].update).toMatchObject({
+      sessionUpdate: "config_option_update",
+    });
+    const updated = (
+      sessionUpdates[0].update as { configOptions: ReturnType<typeof createFastModeConfigOption>[] }
+    ).configOptions;
+    expect(updated).toContainEqual(createFastModeConfigOption(true, true));
+  });
+
+  it("leaves the toggle on and quiet during a rate-limit cooldown", async () => {
+    const { sync, session, sessionUpdates } = setup({ fastModeEnabled: true, withOption: true });
+
+    // cooldown is a transient suspension of an already-enabled fast mode.
+    await sync(SESSION_ID, session, "cooldown");
+
+    expect(session.fastModeEnabled).toBe(true);
+    expect(sessionUpdates).toHaveLength(0);
+  });
+
+  it("never lets a stray cooldown spuriously enable a toggle the user has off", async () => {
+    const { sync, session, sessionUpdates } = setup({ fastModeEnabled: false, withOption: true });
+
+    await sync(SESSION_ID, session, "cooldown");
+
+    expect(session.fastModeEnabled).toBe(false);
+    expect(sessionUpdates).toHaveLength(0);
+  });
+
+  it("clears the toggle when the SDK reports off", async () => {
+    const { sync, session, sessionUpdates } = setup({ fastModeEnabled: true, withOption: true });
+
+    await sync(SESSION_ID, session, "off");
+
+    expect(session.fastModeEnabled).toBe(false);
+    expect(session.configOptions).toContainEqual(createFastModeConfigOption(false, true));
+    expect(sessionUpdates).toHaveLength(1);
+  });
+
+  it("is a no-op when the reported state is undefined or unchanged", async () => {
+    const { sync, session, sessionUpdates } = setup({ fastModeEnabled: false, withOption: true });
+
+    await sync(SESSION_ID, session, undefined);
+    await sync(SESSION_ID, session, "off");
+
+    expect(sessionUpdates).toHaveLength(0);
+  });
+
+  it("preserves the retained setting (no clobber) when the model has no Fast mode option", async () => {
+    // Model without fast support: the SDK reports a capability-driven state, not
+    // the user's intent. We must leave session.fastModeEnabled untouched so it's
+    // correct when a supporting model is reselected — reconciling here was the
+    // original intent-clobber bug.
+    const enabledCase = setup({ fastModeEnabled: true, withOption: false });
+    await enabledCase.sync(SESSION_ID, enabledCase.session, "off");
+    expect(enabledCase.session.fastModeEnabled).toBe(true);
+    expect(enabledCase.sessionUpdates).toHaveLength(0);
+
+    const disabledCase = setup({ fastModeEnabled: false, withOption: false });
+    await disabledCase.sync(SESSION_ID, disabledCase.session, "on");
+    expect(disabledCase.session.fastModeEnabled).toBe(false);
+    expect(disabledCase.sessionUpdates).toHaveLength(0);
+  });
+});
--- a/src/tests/model-resolution.test.ts
+++ b/src/tests/model-resolution.test.ts
@@ -0,0 +1,150 @@
+import { describe, it, expect } from "vitest";
+import { randomUUID } from "crypto";
+import { query } from "@anthropic-ai/claude-agent-sdk";
+import type { ModelInfo } from "@anthropic-ai/claude-agent-sdk";
+import { resolveModelPreference, applyAvailableModelsAllowlist } from "../acp-agent.js";
+
+// Mirrors a real `supportedModels()` response: alias rows carry
+// `resolvedModel`, and "Sonnet 5" has no `major.minor` dot unlike older
+// "claude-opus-4-6"-style ids.
+const LIVE_SHAPED_MODELS: ModelInfo[] = [
+  {
+    value: "default",
+    resolvedModel: "claude-opus-4-8[1m]",
+    displayName: "Default (recommended)",
+    description: "Use the default model (currently Opus 4.8 (1M context))",
+  },
+  {
+    value: "opus[1m]",
+    resolvedModel: "claude-opus-4-8[1m]",
+    displayName: "Opus",
+    description: "Opus 4.8 with 1M context · Best for everyday, complex tasks",
+  },
+  {
+    value: "sonnet",
+    resolvedModel: "claude-sonnet-5",
+    displayName: "Sonnet",
+    description: "Sonnet 5 · Efficient for routine tasks",
+  },
+  {
+    value: "haiku",
+    resolvedModel: "claude-haiku-4-5-20251001",
+    displayName: "Haiku",
+    description: "Haiku 4.5 · Fastest for quick answers",
+  },
+];
+
+describe("resolveModelPreference - resolvedModel matching", () => {
+  it("matches a preference that equals an alias's resolvedModel exactly", () => {
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "claude-sonnet-5")?.value).toBe("sonnet");
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "claude-opus-4-8[1m]")?.value).toBe(
+      "opus[1m]",
+    );
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "claude-haiku-4-5-20251001")?.value).toBe(
+      "haiku",
+    );
+  });
+
+  it("is case-insensitive", () => {
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "CLAUDE-SONNET-5")?.value).toBe("sonnet");
+  });
+
+  it("still resolves plain aliases via the direct-match tier", () => {
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "sonnet")?.value).toBe("sonnet");
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "opus[1m]")?.value).toBe("opus[1m]");
+  });
+
+  it("does not let a retired dated id drift onto a same-family alias of a different generation", () => {
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "claude-sonnet-4-6")).toBeNull();
+  });
+
+  // "opus[1m]"'s `value` has no dotted version, just the context-hint digit
+  // in "[1m]" — unstripped, that reads as version "1" and blocks the match
+  // before the matcher reaches the description's real "4.8".
+  it("does not mistake an alias's context-hint suffix for its version", () => {
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "claude-opus-4-8")?.value).toBe("opus[1m]");
+  });
+
+  it("returns null for a preference that matches nothing", () => {
+    expect(resolveModelPreference(LIVE_SHAPED_MODELS, "claude-gpt-99")).toBeNull();
+  });
+});
+
+describe("applyAvailableModelsAllowlist - resolvedModel matching", () => {
+  it("resolves an allowlist entry pinned to a canonical resolvedModel id", () => {
+    const result = applyAvailableModelsAllowlist(LIVE_SHAPED_MODELS, ["claude-sonnet-5"]);
+    const entry = result.find((m) => m.value === "claude-sonnet-5");
+    expect(entry).toBeDefined();
+    expect(entry?.displayName).toBe("Sonnet");
+  });
+});
+
+describe("applyAvailableModelsAllowlist - modelOverrides", () => {
+  const SDK_MODELS: ModelInfo[] = [
+    { value: "default", displayName: "Default", description: "Default model" },
+    {
+      value: "opus",
+      displayName: "Opus",
+      description: "Claude Opus 4.6",
+      supportsEffort: true,
+      supportedEffortLevels: ["low", "high"],
+    },
+  ];
+
+  it("surfaces the override target as the value while keeping the alias's display metadata", () => {
+    // The override target is an opaque Bedrock ARN with no "opus" substring,
+    // so matching against it (instead of the "claude-opus-4-6" alias) would
+    // find nothing and silently drop displayName/description/supportsEffort.
+    const overrides = {
+      "claude-opus-4-6": "arn:aws:bedrock:us-west-2:111122223333:inference-profile/custom-7f3a",
+    };
+    const result = applyAvailableModelsAllowlist(SDK_MODELS, ["claude-opus-4-6"], overrides);
+
+    const entry = result.find((m) => m.value === overrides["claude-opus-4-6"]);
+    expect(entry).toEqual({
+      value: overrides["claude-opus-4-6"],
+      displayName: "Opus",
+      description: "Claude Opus 4.6",
+      supportsEffort: true,
+      supportedEffortLevels: ["low", "high"],
+    });
+  });
+});
+
+// Runs against the real SDK (no mocks) so the fixture above is flagged the
+// moment the SDK's actual model list shape drifts from it. Requires a usable
+// ANTHROPIC_API_KEY, hence opt-in via RUN_INTEGRATION_TESTS.
+describe.skipIf(!process.env.RUN_INTEGRATION_TESTS)("model resolution (real SDK)", () => {
+  it("every model's resolvedModel (when present) resolves back to that same row", async () => {
+    const q = query({ prompt: "hi", options: { sessionId: randomUUID() } });
+    try {
+      const models = await q.supportedModels();
+      expect(models.length).toBeGreaterThan(0);
+
+      for (const model of models) {
+        // "default" shares a resolvedModel with the CLI's recommended named
+        // alias, and resolution intentionally prefers that alias on a tie.
+        if (!model.resolvedModel || model.value === "default") continue;
+        const resolved = resolveModelPreference(models, model.resolvedModel);
+        expect(resolved?.value).toBe(model.value);
+      }
+    } finally {
+      q.return(undefined);
+    }
+  }, 30000);
+
+  it("resolves the well-known 'sonnet' and 'opus' aliases to a model bearing their family name", async () => {
+    const q = query({ prompt: "hi", options: { sessionId: randomUUID() } });
+    try {
+      const models = await q.supportedModels();
+
+      const sonnet = resolveModelPreference(models, "sonnet");
+      expect(sonnet?.resolvedModel?.toLowerCase()).toContain("sonnet");
+
+      const opus = resolveModelPreference(models, "opus");
+      expect(opus?.resolvedModel?.toLowerCase()).toContain("opus");
+    } finally {
+      q.return(undefined);
+    }
+  }, 30000);
+});
--- a/src/tests/tools.test.ts
+++ b/src/tests/tools.test.ts
@@ -1614,6 +1614,68 @@ describe("toolInfoFromToolUse - undefined input regression", () => {
    const info = toolInfoFromToolUse(toolUse, false);
    expect(info.title).toBe("Update TODOs");
  });
+
+  it("ReportFindings with undefined input should not throw", () => {
+    const toolUse = { name: "ReportFindings", id: "toolu_findings_undef", input: undefined };
+    const info = toolInfoFromToolUse(toolUse, false);
+    expect(info.title).toBe("Report findings: none found");
+    expect(info.content).toEqual([]);
+  });
+});
+
+describe("toolInfoFromToolUse - ReportFindings", () => {
+  it("should summarize findings count and list each in content", () => {
+    const toolUse = {
+      name: "ReportFindings",
+      id: "toolu_findings_1",
+      input: {
+        findings: [
+          {
+            file: "src/foo.ts",
+            line: 42,
+            summary: "Off-by-one in loop bound",
+            failure_scenario: "Empty array → index out of bounds crash",
+          },
+          {
+            file: "src/bar.ts",
+            summary: "Unhandled promise rejection",
+            failure_scenario: "Network failure → unhandled rejection",
+          },
+        ],
+      },
+    };
+
+    const info = toolInfoFromToolUse(toolUse, false);
+
+    expect(info.kind).toBe("think");
+    expect(info.title).toBe("Report 2 findings");
+    expect(info.content).toEqual([
+      {
+        type: "content",
+        content: { type: "text", text: "**src/foo.ts:42** — Off-by-one in loop bound" },
+      },
+      {
+        type: "content",
+        content: { type: "text", text: "**src/bar.ts** — Unhandled promise rejection" },
+      },
+    ]);
+  });
+
+  it("should report a singular title and empty findings array", () => {
+    const oneFinding = {
+      name: "ReportFindings",
+      id: "toolu_findings_2",
+      input: { findings: [{ file: "src/baz.ts", summary: "Leak", failure_scenario: "..." }] },
+    };
+    expect(toolInfoFromToolUse(oneFinding, false).title).toBe("Report 1 finding");
+
+    const noFindings = {
+      name: "ReportFindings",
+      id: "toolu_findings_3",
+      input: { findings: [] },
+    };
+    expect(toolInfoFromToolUse(noFindings, false).title).toBe("Report findings: none found");
+  });
 });

 describe("planEntries - undefined input regression", () => {
--- a/src/tools.ts
+++ b/src/tools.ts
@@ -15,6 +15,7 @@ import {
  FileWriteInput,
  GlobInput,
  GrepInput,
+  ReportFindingsInput,
  TaskCreateInput,
  TaskCreateOutput,
  TaskUpdateInput,
@@ -371,6 +372,25 @@ export function toolInfoFromToolUse(
      };
    }

+    case "ReportFindings": {
+      const input = toolUse.input as ReportFindingsInput | undefined;
+      const findings = input?.findings ?? [];
+      return {
+        title:
+          findings.length === 0
+            ? "Report findings: none found"
+            : `Report ${findings.length} finding${findings.length === 1 ? "" : "s"}`,
+        kind: "think",
+        content: findings.map((finding) => ({
+          type: "content" as const,
+          content: {
+            type: "text" as const,
+            text: `**${finding.file}${finding.line ? `:${finding.line}` : ""}** — ${finding.summary}`,
+          },
+        })),
+      };
+    }
+
    case "TaskCreate": {
      const input = toolUse.input as TaskCreateInput | undefined;
      return {