diff --git a/src/agents/agent-command.ts b/src/agents/agent-command.ts
index 993a253156f..319bdf88800 100644
--- a/src/agents/agent-command.ts
+++ b/src/agents/agent-command.ts
@@ -48,6 +48,7 @@ import { resolveAgentRunContext } from "./command/run-context.js";
 import { resolveSession } from "./command/session.js";
 import type { AgentCommandIngressOpts, AgentCommandOpts } from "./command/types.js";
 import { DEFAULT_MODEL, DEFAULT_PROVIDER } from "./defaults.js";
+import { resolveFastModeState } from "./fast-mode.js";
 import { AGENT_LANE_SUBAGENT } from "./lanes.js";
 import { LiveSessionModelSwitchError } from "./live-model-switch.js";
 import { loadModelCatalog } from "./model-catalog.js";
@@ -978,6 +979,13 @@ async function agentCommandInternal(
               body,
               isFallbackRetry,
               resolvedThinkLevel,
+              fastMode: resolveFastModeState({
+                cfg,
+                provider: providerOverride,
+                model: modelOverride,
+                agentId: sessionAgentId,
+                sessionEntry,
+              }).enabled,
               timeoutMs,
               runId,
               opts,
diff --git a/src/agents/command/attempt-execution.ts b/src/agents/command/attempt-execution.ts
index 7ad64588577..99aa33fbb79 100644
--- a/src/agents/command/attempt-execution.ts
+++ b/src/agents/command/attempt-execution.ts
@@ -324,6 +324,7 @@ export function runAgentAttempt(params: {
   body: string;
   isFallbackRetry: boolean;
   resolvedThinkLevel: ThinkLevel;
+  fastMode?: boolean;
   timeoutMs: number;
   runId: string;
   opts: AgentCommandOpts & { senderIsOwner: boolean };
@@ -577,6 +578,7 @@ export function runAgentAttempt(params: {
     authProfileId,
     authProfileIdSource: authProfileId ? harnessAuthSelection.authProfileIdSource : undefined,
     thinkLevel: params.resolvedThinkLevel,
+    fastMode: params.fastMode,
     verboseLevel: params.resolvedVerboseLevel,
     timeoutMs: params.timeoutMs,
     runId: params.runId,
diff --git a/src/agents/fast-mode.test.ts b/src/agents/fast-mode.test.ts
index e4ec70edd22..59428116ee5 100644
--- a/src/agents/fast-mode.test.ts
+++ b/src/agents/fast-mode.test.ts
@@ -54,6 +54,69 @@ describe("resolveFastModeState", () => {
     expect(state.source).toBe("config");
   });
 
+  it("uses model config when the runtime passes a provider-qualified model ref", () => {
+    const cfg = {
+      agents: {
+        defaults: {
+          models: {
+            "openai/gpt-5.5": { params: { fastMode: true } },
+          },
+        },
+      },
+    } as OpenClawConfig;
+
+    const state = resolveFastModeState({
+      cfg,
+      provider: "openai",
+      model: "openai/gpt-5.5",
+    });
+
+    expect(state.enabled).toBe(true);
+    expect(state.source).toBe("config");
+  });
+
+  it("uses canonical provider/model config for slash-containing model ids", () => {
+    const cfg = {
+      agents: {
+        defaults: {
+          models: {
+            "openrouter/anthropic/claude-sonnet-4-6": { params: { fastMode: true } },
+          },
+        },
+      },
+    } as OpenClawConfig;
+
+    const state = resolveFastModeState({
+      cfg,
+      provider: "openrouter",
+      model: "anthropic/claude-sonnet-4-6",
+    });
+
+    expect(state.enabled).toBe(true);
+    expect(state.source).toBe("config");
+  });
+
+  it("does not use another provider's slash-containing model config", () => {
+    const cfg = {
+      agents: {
+        defaults: {
+          models: {
+            "anthropic/claude-sonnet-4-6": { params: { fastMode: true } },
+          },
+        },
+      },
+    } as OpenClawConfig;
+
+    const state = resolveFastModeState({
+      cfg,
+      provider: "openrouter",
+      model: "anthropic/claude-sonnet-4-6",
+    });
+
+    expect(state.enabled).toBe(false);
+    expect(state.source).toBe("default");
+  });
+
   it("defaults to off when unset", () => {
     const state = resolveFastModeState({
       cfg: {} as OpenClawConfig,
diff --git a/src/agents/fast-mode.ts b/src/agents/fast-mode.ts
index 4851838fc1c..b9b09220749 100644
--- a/src/agents/fast-mode.ts
+++ b/src/agents/fast-mode.ts
@@ -2,6 +2,7 @@ import { normalizeFastMode } from "../auto-reply/thinking.shared.js";
 import type { SessionEntry } from "../config/sessions.js";
 import type { OpenClawConfig } from "../config/types.openclaw.js";
 import { resolveAgentConfig } from "./agent-scope.js";
+import { modelKey } from "./model-ref-shared.js";
 
 export type FastModeState = {
   enabled: boolean;
@@ -13,8 +14,8 @@ function resolveConfiguredFastModeRaw(params: {
   provider: string;
   model: string;
 }): unknown {
-  const modelKey = `${params.provider}/${params.model}`;
-  const modelConfig = params.cfg?.agents?.defaults?.models?.[modelKey];
+  const modelConfig =
+    params.cfg?.agents?.defaults?.models?.[modelKey(params.provider, params.model)];
   return modelConfig?.params?.fastMode ?? modelConfig?.params?.fast_mode;
 }
 
diff --git a/src/commands/agent.test.ts b/src/commands/agent.test.ts
index 30e4e43b753..347561a49bd 100644
--- a/src/commands/agent.test.ts
+++ b/src/commands/agent.test.ts
@@ -105,6 +105,7 @@ vi.mock("../agents/command/attempt-execution.runtime.js", () => {
         authProfileId,
         authProfileIdSource: authProfileId ? sessionEntry?.authProfileOverrideSource : undefined,
         thinkLevel: params.resolvedThinkLevel,
+        fastMode: params.fastMode,
         verboseLevel: params.resolvedVerboseLevel,
         timeoutMs: params.timeoutMs,
         runId: params.runId,
@@ -385,6 +386,29 @@ describe("agentCommand", () => {
     });
   });
 
+  it("passes configured fast mode to embedded runs", async () => {
+    await withTempHome(async (home) => {
+      const store = path.join(home, "sessions.json");
+      mockConfig(home, store, {
+        model: "openai/gpt-5.5",
+        models: {
+          "openai/gpt-5.5": { params: { fastMode: true } },
+        },
+      });
+
+      await agentCommand({ message: "ping", agentId: "main" }, runtime);
+
+      const callArgs = getLastEmbeddedCall();
+      expect(callArgs).toEqual(
+        expect.objectContaining({
+          provider: "openai",
+          model: "gpt-5.5",
+          fastMode: true,
+        }),
+      );
+    });
+  });
+
   it("does not load the full model catalog for trusted explicit overrides without an allowlist", async () => {
     await withTempHome(async (home) => {
       const store = path.join(home, "sessions.json");