diff --git a/docs/tools/acp-agents.md b/docs/tools/acp-agents.md
index 3eda981e8db..005680e70f8 100644
--- a/docs/tools/acp-agents.md
+++ b/docs/tools/acp-agents.md
@@ -560,6 +560,10 @@ Two ways to start an ACP session:
   normalize OpenAI refs such as `openai/gpt-5.4` to Codex ACP startup
   config before `session/new`; slash forms such as `openai/gpt-5.4/high`
   also set Codex ACP reasoning effort.
+  When omitted, `sessions_spawn({ runtime: "acp" })` uses existing
+  subagent model defaults (`agents.defaults.subagents.model` or
+  `agents.list[].subagents.model`) when configured; otherwise it lets the
+  ACP harness use its own default model.
   Other harnesses must advertise ACP `models` and support
   `session/set_model`; otherwise OpenClaw/acpx fails clearly instead of
   silently falling back to the target agent default.
@@ -568,6 +572,9 @@ Two ways to start an ACP session:
   Explicit thinking/reasoning effort. For Codex ACP, `minimal` maps to
   low effort, `low`/`medium`/`high`/`xhigh` map directly, and `off`
   omits the reasoning-effort startup override.
+  When omitted, ACP spawns use existing subagent thinking defaults and
+  per-model `agents.defaults.models["provider/model"].params.thinking`
+  for the selected model.
 </ParamField>
 
 ## Spawn bind and thread modes
diff --git a/docs/tools/subagents.md b/docs/tools/subagents.md
index 806e2d5ab49..958f07a7600 100644
--- a/docs/tools/subagents.md
+++ b/docs/tools/subagents.md
@@ -139,8 +139,8 @@ session to confirm the effective tool list.
 
 **Defaults:**
 
-- **Model:** inherits the caller unless you set `agents.defaults.subagents.model` (or per-agent `agents.list[].subagents.model`); an explicit `sessions_spawn.model` still wins.
-- **Thinking:** inherits the caller unless you set `agents.defaults.subagents.thinking` (or per-agent `agents.list[].subagents.thinking`); an explicit `sessions_spawn.thinking` still wins.
+- **Model:** native sub-agents inherit the caller unless you set `agents.defaults.subagents.model` (or per-agent `agents.list[].subagents.model`). ACP runtime spawns use the same configured subagent model when present; otherwise the ACP harness keeps its own default. An explicit `sessions_spawn.model` still wins.
+- **Thinking:** native sub-agents inherit the caller unless you set `agents.defaults.subagents.thinking` (or per-agent `agents.list[].subagents.thinking`). ACP runtime spawns also apply `agents.defaults.models["provider/model"].params.thinking` for the selected model. An explicit `sessions_spawn.thinking` still wins.
 - **Run timeout:** if `sessions_spawn.runTimeoutSeconds` is omitted, OpenClaw uses `agents.defaults.subagents.runTimeoutSeconds` when set; otherwise it falls back to `0` (no timeout).
 - **Task delivery:** native sub-agents receive the delegated task in their first visible `[Subagent Task]` message. The sub-agent system prompt carries runtime rules and routing context, not a hidden duplicate of the task.
 
diff --git a/src/agents/acp-spawn.test.ts b/src/agents/acp-spawn.test.ts
index ffcf75d84c5..486494c4160 100644
--- a/src/agents/acp-spawn.test.ts
+++ b/src/agents/acp-spawn.test.ts
@@ -929,6 +929,129 @@ describe("spawnAcpDirect", () => {
     expect(initInput.sessionKey).toMatch(/^agent:codex:acp:/);
   });
 
+  it("applies existing subagent model and model-profile thinking defaults to ACP runtime options", async () => {
+    replaceSpawnConfig({
+      ...createDefaultSpawnConfig(),
+      agents: {
+        defaults: {
+          subagents: {
+            allowAgents: ["codex"],
+            maxSpawnDepth: 2,
+            model: "openai/gpt-5.4",
+          },
+          models: {
+            "openai/gpt-5.4": {
+              params: { thinking: "high" },
+            },
+          },
+        },
+      },
+    });
+
+    const result = await spawnAcpDirect(
+      {
+        task: "Investigate flaky tests",
+        agentId: "codex",
+      },
+      {
+        agentSessionKey: "agent:main:main",
+      },
+    );
+
+    expectAcceptedSpawn(result);
+    expectInitializeSessionFields({
+      agent: "codex",
+      runtimeOptions: {
+        model: "openai/gpt-5.4",
+        thinking: "high",
+      },
+    });
+  });
+
+  it("uses configured runtime=acp agent defaults before launching the external ACP agent", async () => {
+    replaceSpawnConfig({
+      ...createDefaultSpawnConfig(),
+      agents: {
+        list: [
+          {
+            id: "codex-acp",
+            runtime: {
+              type: "acp",
+              acp: { agent: "codex" },
+            },
+            subagents: {
+              model: "openai/gpt-5.5",
+              thinking: "low",
+            },
+          },
+        ],
+        defaults: {
+          subagents: {
+            allowAgents: ["codex"],
+            maxSpawnDepth: 2,
+          },
+        },
+      },
+    });
+
+    const result = await spawnAcpDirect(
+      {
+        task: "Investigate flaky tests",
+        agentId: "codex-acp",
+      },
+      {
+        agentSessionKey: "agent:main:main",
+      },
+    );
+
+    expectAcceptedSpawn(result);
+    expectInitializeSessionFields({
+      agent: "codex",
+      runtimeOptions: {
+        model: "openai/gpt-5.5",
+        thinking: "low",
+      },
+    });
+  });
+
+  it("does not treat a configured runtime=acp agent primary model as an ACP startup model", async () => {
+    replaceSpawnConfig({
+      ...createDefaultSpawnConfig(),
+      agents: {
+        list: [
+          {
+            id: "codex-acp",
+            runtime: {
+              type: "acp",
+              acp: { agent: "codex" },
+            },
+            model: "anthropic/claude-sonnet-4-6",
+          },
+        ],
+        defaults: {
+          subagents: {
+            allowAgents: ["codex"],
+            maxSpawnDepth: 2,
+          },
+        },
+      },
+    });
+
+    const result = await spawnAcpDirect(
+      {
+        task: "Investigate flaky tests",
+        agentId: "codex-acp",
+      },
+      {
+        agentSessionKey: "agent:main:main",
+      },
+    );
+
+    expectAcceptedSpawn(result);
+    const initInput = expectInitializeSessionFields({ agent: "codex" });
+    expect(initInput.runtimeOptions).toBeUndefined();
+  });
+
   it("applies ACP spawn run timeout to runtime options and dispatch", async () => {
     const result = await spawnAcpDirect(
       {
diff --git a/src/agents/acp-spawn.ts b/src/agents/acp-spawn.ts
index 0c0ac9259e6..31ba2aba98e 100644
--- a/src/agents/acp-spawn.ts
+++ b/src/agents/acp-spawn.ts
@@ -17,6 +17,7 @@ import {
 } from "../acp/control-plane/spawn.js";
 import { isAcpEnabledByPolicy, resolveAcpAgentPolicyError } from "../acp/policy.js";
 import { DEFAULT_HEARTBEAT_EVERY } from "../auto-reply/heartbeat.js";
+import { formatThinkingLevels } from "../auto-reply/thinking.js";
 import {
   resolveChannelDefaultBindingPlacement,
   resolveInboundConversationResolution,
@@ -82,6 +83,10 @@ import {
   inheritedToolDenyPatch,
 } from "./inherited-tool-deny.js";
 import { AGENT_LANE_SUBAGENT } from "./lanes.js";
+import {
+  resolveConfiguredSubagentSpawnModelSelection,
+  resolveThinkingDefault,
+} from "./model-selection.js";
 import { resolveSandboxRuntimeStatus } from "./sandbox/runtime-status.js";
 import { resolveRequesterOriginForChild } from "./spawn-requester-origin.js";
 import { resolveSpawnedWorkspaceInheritance } from "./spawned-context.js";
@@ -93,6 +98,8 @@ import {
 } from "./subagent-capabilities.js";
 import { getSubagentDepthFromSessionStore } from "./subagent-depth.js";
 import { countActiveRunsForSession, getSubagentRunByChildSessionKey } from "./subagent-registry.js";
+import { splitModelRef } from "./subagent-spawn-plan.js";
+import { resolveSubagentThinkingOverride } from "./subagent-spawn-thinking.js";
 import { resolveSubagentTargetPolicy } from "./subagent-target-policy.js";
 import { resolveInternalSessionKey, resolveMainSessionAlias } from "./tools/sessions-helpers.js";
 
@@ -437,7 +444,7 @@ function hasSessionLocalHeartbeatRelayRoute(params: {
 function resolveTargetAcpAgentId(params: {
   requestedAgentId?: string;
   cfg: OpenClawConfig;
-}): { ok: true; agentId: string } | { ok: false; error: string } {
+}): { ok: true; agentId: string; configAgentId?: string } | { ok: false; error: string } {
   const requested = normalizeOptionalAgentId(params.requestedAgentId);
   if (requested) {
     const configuredAgent = params.cfg.agents?.list?.find(
@@ -447,6 +454,7 @@ function resolveTargetAcpAgentId(params: {
       return {
         ok: true,
         agentId: normalizeOptionalAgentId(configuredAgent.runtime.acp?.agent) ?? requested,
+        configAgentId: requested,
       };
     }
     if (configuredAgent && !isExplicitlyAllowedAcpAgent(params.cfg, requested)) {
@@ -458,7 +466,11 @@ function resolveTargetAcpAgentId(params: {
           'Use runtime="acp" only with external ACP harness ids such as codex, claude, droid, gemini, or opencode, or configure agents.list[].runtime.type="acp" with runtime.acp.agent.',
       };
     }
-    return { ok: true, agentId: requested };
+    return {
+      ok: true,
+      agentId: requested,
+      ...(configuredAgent ? { configAgentId: requested } : {}),
+    };
   }
 
   const configuredDefault = normalizeOptionalAgentId(params.cfg.acp?.defaultAgent);
@@ -975,15 +987,71 @@ function validateAcpResumeSessionOwnership(params: {
   };
 }
 
+type AcpSpawnRuntimeOptions = {
+  model?: string;
+  thinking?: string;
+  timeoutSeconds?: number;
+};
+
+function resolveAcpSpawnRuntimeOptions(params: {
+  cfg: OpenClawConfig;
+  targetAgentId: string;
+  configAgentId?: string;
+  model?: string;
+  thinking?: string;
+  runTimeoutSeconds?: number;
+}): { ok: true; runtimeOptions?: AcpSpawnRuntimeOptions } | { ok: false; error: string } {
+  const policyAgentId = params.configAgentId ?? params.targetAgentId;
+  const model = resolveConfiguredSubagentSpawnModelSelection({
+    cfg: params.cfg,
+    agentId: policyAgentId,
+    modelOverride: params.model,
+    includeAgentPrimary: false,
+  });
+  const targetAgentConfig = resolveAgentConfig(params.cfg, policyAgentId);
+  const thinkingPlan = resolveSubagentThinkingOverride({
+    cfg: params.cfg,
+    targetAgentConfig,
+    thinkingOverrideRaw: params.thinking,
+  });
+  if (thinkingPlan.status === "error") {
+    const { provider, model: modelId } = splitModelRef(model);
+    return {
+      ok: false,
+      error: `Invalid thinking level "${thinkingPlan.thinkingCandidateRaw}". Use one of: ${formatThinkingLevels(provider, modelId)}.`,
+    };
+  }
+
+  let thinking = thinkingPlan.thinkingOverride;
+  if (!thinking && model) {
+    const { provider, model: modelId } = splitModelRef(model);
+    if (provider && modelId) {
+      thinking = resolveThinkingDefault({
+        cfg: params.cfg,
+        provider,
+        model: modelId,
+      });
+    }
+  }
+
+  const runtimeOptions =
+    model || thinking || params.runTimeoutSeconds
+      ? {
+          ...(model ? { model } : {}),
+          ...(thinking ? { thinking } : {}),
+          ...(params.runTimeoutSeconds ? { timeoutSeconds: params.runTimeoutSeconds } : {}),
+        }
+      : undefined;
+  return { ok: true, runtimeOptions };
+}
+
 async function initializeAcpSpawnRuntime(params: {
   cfg: OpenClawConfig;
   sessionKey: string;
   targetAgentId: string;
   runtimeMode: AcpRuntimeSessionMode;
   resumeSessionId?: string;
-  model?: string;
-  thinking?: string;
-  runTimeoutSeconds?: number;
+  runtimeOptions?: AcpSpawnRuntimeOptions;
   cwd?: string;
 }): Promise<AcpSpawnInitializedRuntime> {
   const storePath = resolveStorePath(params.cfg.session?.store, { agentId: params.targetAgentId });
@@ -1008,14 +1076,7 @@ async function initializeAcpSpawnRuntime(params: {
     agent: params.targetAgentId,
     mode: params.runtimeMode,
     resumeSessionId: params.resumeSessionId,
-    runtimeOptions:
-      params.model || params.thinking || params.runTimeoutSeconds
-        ? {
-            ...(params.model ? { model: params.model } : {}),
-            ...(params.thinking ? { thinking: params.thinking } : {}),
-            ...(params.runTimeoutSeconds ? { timeoutSeconds: params.runTimeoutSeconds } : {}),
-          }
-        : undefined,
+    runtimeOptions: params.runtimeOptions,
     cwd: params.cwd,
     backendId: params.cfg.acp?.backend,
   });
@@ -1320,6 +1381,21 @@ export async function spawnAcpDirect(
       error: resumeAuthorization.error,
     });
   }
+  const runtimeOptionsResult = resolveAcpSpawnRuntimeOptions({
+    cfg,
+    targetAgentId,
+    configAgentId: targetAgentResult.configAgentId,
+    model: params.model,
+    thinking: params.thinking,
+    runTimeoutSeconds: params.runTimeoutSeconds,
+  });
+  if (!runtimeOptionsResult.ok) {
+    return createAcpSpawnFailure({
+      status: "error",
+      errorCode: "spawn_failed",
+      error: runtimeOptionsResult.error,
+    });
+  }
   const { effectiveStreamToParent } = resolveAcpSpawnStreamPlan({
     spawnMode,
     requestThreadBinding,
@@ -1392,9 +1468,7 @@ export async function spawnAcpDirect(
       targetAgentId,
       runtimeMode,
       resumeSessionId: params.resumeSessionId,
-      model: params.model,
-      thinking: params.thinking,
-      runTimeoutSeconds: params.runTimeoutSeconds,
+      runtimeOptions: runtimeOptionsResult.runtimeOptions,
       cwd: runtimeCwd,
     });
     initializedRuntime = initializedSession.runtimeCloseHandle;
diff --git a/src/agents/model-selection.ts b/src/agents/model-selection.ts
index 826b1141ca2..8b4483d3f23 100644
--- a/src/agents/model-selection.ts
+++ b/src/agents/model-selection.ts
@@ -323,12 +323,13 @@ function resolveAllowedFallbacks(params: { cfg: OpenClawConfig; agentId?: string
 export function resolveSubagentConfiguredModelSelection(params: {
   cfg: OpenClawConfig;
   agentId: string;
+  includeAgentPrimary?: boolean;
 }): string | undefined {
   const agentConfig = resolveAgentConfig(params.cfg, params.agentId);
   return (
     normalizeModelSelection(agentConfig?.subagents?.model) ??
     normalizeModelSelection(params.cfg.agents?.defaults?.subagents?.model) ??
-    normalizeModelSelection(agentConfig?.model)
+    (params.includeAgentPrimary === false ? undefined : normalizeModelSelection(agentConfig?.model))
   );
 }
 
@@ -361,12 +362,16 @@ export function resolveSubagentSpawnModelSelection(params: {
     cfg: params.cfg,
     agentId: params.agentId,
   });
+  const configured = resolveConfiguredSubagentSpawnModelSelection({
+    cfg: params.cfg,
+    agentId: params.agentId,
+    modelOverride: params.modelOverride,
+    defaultProvider: runtimeDefault.provider,
+  });
+  if (configured) {
+    return configured;
+  }
   const raw =
-    normalizeModelSelection(params.modelOverride) ??
-    resolveSubagentConfiguredModelSelection({
-      cfg: params.cfg,
-      agentId: params.agentId,
-    }) ??
     normalizeModelSelection(resolveAgentModelPrimaryValue(params.cfg.agents?.defaults?.model)) ??
     `${runtimeDefault.provider}/${runtimeDefault.model}`;
   const aliasIndex = buildModelAliasIndex({
@@ -376,6 +381,36 @@ export function resolveSubagentSpawnModelSelection(params: {
   return resolveModelThroughAliases(raw, aliasIndex);
 }
 
+export function resolveConfiguredSubagentSpawnModelSelection(params: {
+  cfg: OpenClawConfig;
+  agentId: string;
+  modelOverride?: unknown;
+  defaultProvider?: string;
+  includeAgentPrimary?: boolean;
+}): string | undefined {
+  const raw =
+    normalizeModelSelection(params.modelOverride) ??
+    resolveSubagentConfiguredModelSelection({
+      cfg: params.cfg,
+      agentId: params.agentId,
+      includeAgentPrimary: params.includeAgentPrimary,
+    });
+  if (!raw) {
+    return undefined;
+  }
+  const defaultProvider =
+    normalizeOptionalString(params.defaultProvider) ??
+    resolveDefaultModelForAgent({
+      cfg: params.cfg,
+      agentId: params.agentId,
+    }).provider;
+  const aliasIndex = buildModelAliasIndex({
+    cfg: params.cfg,
+    defaultProvider,
+  });
+  return resolveModelThroughAliases(raw, aliasIndex);
+}
+
 export function buildAllowedModelSet(
   params: {
     cfg: OpenClawConfig;
diff --git a/src/agents/openclaw-tools.subagents.sessions-spawn.model.test.ts b/src/agents/openclaw-tools.subagents.sessions-spawn.model.test.ts
index 9a9be8495eb..0c03d2b8d59 100644
--- a/src/agents/openclaw-tools.subagents.sessions-spawn.model.test.ts
+++ b/src/agents/openclaw-tools.subagents.sessions-spawn.model.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from "vitest";
 import type { OpenClawConfig } from "../config/config.js";
 import { DEFAULT_MODEL, DEFAULT_PROVIDER } from "./defaults.js";
+import { resolveConfiguredSubagentSpawnModelSelection } from "./model-selection.js";
 import {
   resolveConfiguredSubagentRunTimeoutSeconds,
   resolveSubagentModelAndThinkingPlan,
@@ -98,6 +99,23 @@ describe("subagent spawn model + thinking plan", () => {
     expect(plan.initialSessionPatch.modelOverrideSource).toBe("auto");
   });
 
+  it("can resolve only explicit or configured subagent model selections", () => {
+    expect(
+      resolveConfiguredSubagentSpawnModelSelection({
+        cfg: createConfig(),
+        agentId: "research",
+      }),
+    ).toBeUndefined();
+    expect(
+      resolveConfiguredSubagentSpawnModelSelection({
+        cfg: createConfig({
+          agents: { defaults: { subagents: { model: "minimax/MiniMax-M2.7" } } },
+        }),
+        agentId: "research",
+      }),
+    ).toBe("minimax/MiniMax-M2.7");
+  });
+
   it("prefers per-agent subagent model over defaults", () => {
     const cfg = createConfig({
       agents: {