diff --git a/src/config/agent-limits.ts b/src/config/agent-limits.ts
index 0a1733c038..5a0e4a42a2 100644
--- a/src/config/agent-limits.ts
+++ b/src/config/agent-limits.ts
@@ -1,2 +1,20 @@
+import type { ClawdbotConfig } from "./types.js";
+
 export const DEFAULT_AGENT_MAX_CONCURRENT = 4;
 export const DEFAULT_SUBAGENT_MAX_CONCURRENT = 8;
+
+export function resolveAgentMaxConcurrent(cfg?: ClawdbotConfig): number {
+  const raw = cfg?.agents?.defaults?.maxConcurrent;
+  if (typeof raw === "number" && Number.isFinite(raw)) {
+    return Math.max(1, Math.floor(raw));
+  }
+  return DEFAULT_AGENT_MAX_CONCURRENT;
+}
+
+export function resolveSubagentMaxConcurrent(cfg?: ClawdbotConfig): number {
+  const raw = cfg?.agents?.defaults?.subagents?.maxConcurrent;
+  if (typeof raw === "number" && Number.isFinite(raw)) {
+    return Math.max(1, Math.floor(raw));
+  }
+  return DEFAULT_SUBAGENT_MAX_CONCURRENT;
+}
diff --git a/src/config/config.agent-concurrency-defaults.test.ts b/src/config/config.agent-concurrency-defaults.test.ts
new file mode 100644
index 0000000000..2f53bc6056
--- /dev/null
+++ b/src/config/config.agent-concurrency-defaults.test.ts
@@ -0,0 +1,62 @@
+import fs from "node:fs/promises";
+import path from "node:path";
+import { describe, expect, it, vi } from "vitest";
+import {
+  DEFAULT_AGENT_MAX_CONCURRENT,
+  DEFAULT_SUBAGENT_MAX_CONCURRENT,
+  resolveAgentMaxConcurrent,
+  resolveSubagentMaxConcurrent,
+} from "./agent-limits.js";
+import { withTempHome } from "./test-helpers.js";
+
+describe("agent concurrency defaults", () => {
+  it("resolves defaults when unset", () => {
+    expect(resolveAgentMaxConcurrent({})).toBe(DEFAULT_AGENT_MAX_CONCURRENT);
+    expect(resolveSubagentMaxConcurrent({})).toBe(DEFAULT_SUBAGENT_MAX_CONCURRENT);
+  });
+
+  it("resolves configured values", () => {
+    const cfg = {
+      agents: {
+        defaults: {
+          maxConcurrent: 6,
+          subagents: { maxConcurrent: 9 },
+        },
+      },
+    };
+    expect(resolveAgentMaxConcurrent(cfg)).toBe(6);
+    expect(resolveSubagentMaxConcurrent(cfg)).toBe(9);
+  });
+
+  it("clamps invalid values to at least 1", () => {
+    const cfg = {
+      agents: {
+        defaults: {
+          maxConcurrent: 0,
+          subagents: { maxConcurrent: -3 },
+        },
+      },
+    };
+    expect(resolveAgentMaxConcurrent(cfg)).toBe(1);
+    expect(resolveSubagentMaxConcurrent(cfg)).toBe(1);
+  });
+
+  it("injects defaults on load", async () => {
+    await withTempHome(async (home) => {
+      const configDir = path.join(home, ".clawdbot");
+      await fs.mkdir(configDir, { recursive: true });
+      await fs.writeFile(
+        path.join(configDir, "clawdbot.json"),
+        JSON.stringify({}, null, 2),
+        "utf-8",
+      );
+
+      vi.resetModules();
+      const { loadConfig } = await import("./config.js");
+      const cfg = loadConfig();
+
+      expect(cfg.agents?.defaults?.maxConcurrent).toBe(DEFAULT_AGENT_MAX_CONCURRENT);
+      expect(cfg.agents?.defaults?.subagents?.maxConcurrent).toBe(DEFAULT_SUBAGENT_MAX_CONCURRENT);
+    });
+  });
+});
diff --git a/src/gateway/server-lanes.ts b/src/gateway/server-lanes.ts
index 95de0586f6..9e05edd226 100644
--- a/src/gateway/server-lanes.ts
+++ b/src/gateway/server-lanes.ts
@@ -1,18 +1,9 @@
 import type { loadConfig } from "../config/config.js";
-import {
-  DEFAULT_AGENT_MAX_CONCURRENT,
-  DEFAULT_SUBAGENT_MAX_CONCURRENT,
-} from "../config/agent-limits.js";
+import { resolveAgentMaxConcurrent, resolveSubagentMaxConcurrent } from "../config/agent-limits.js";
 import { setCommandLaneConcurrency } from "../process/command-queue.js";
 
 export function applyGatewayLaneConcurrency(cfg: ReturnType<typeof loadConfig>) {
   setCommandLaneConcurrency("cron", cfg.cron?.maxConcurrentRuns ?? 1);
-  setCommandLaneConcurrency(
-    "main",
-    cfg.agents?.defaults?.maxConcurrent ?? DEFAULT_AGENT_MAX_CONCURRENT,
-  );
-  setCommandLaneConcurrency(
-    "subagent",
-    cfg.agents?.defaults?.subagents?.maxConcurrent ?? DEFAULT_SUBAGENT_MAX_CONCURRENT,
-  );
+  setCommandLaneConcurrency("main", resolveAgentMaxConcurrent(cfg));
+  setCommandLaneConcurrency("subagent", resolveSubagentMaxConcurrent(cfg));
 }
diff --git a/src/gateway/server-reload-handlers.ts b/src/gateway/server-reload-handlers.ts
index 31c643db88..6728228dbe 100644
--- a/src/gateway/server-reload-handlers.ts
+++ b/src/gateway/server-reload-handlers.ts
@@ -8,10 +8,7 @@ import {
   setGatewaySigusr1RestartPolicy,
 } from "../infra/restart.js";
 import { setCommandLaneConcurrency } from "../process/command-queue.js";
-import {
-  DEFAULT_AGENT_MAX_CONCURRENT,
-  DEFAULT_SUBAGENT_MAX_CONCURRENT,
-} from "../config/agent-limits.js";
+import { resolveAgentMaxConcurrent, resolveSubagentMaxConcurrent } from "../config/agent-limits.js";
 import { isTruthyEnvValue } from "../infra/env.js";
 import type { ChannelKind, GatewayReloadPlan } from "./config-reload.js";
 import { resolveHooksConfig } from "./hooks.js";
@@ -131,14 +128,8 @@ export function createGatewayReloadHandlers(params: {
     }
 
     setCommandLaneConcurrency("cron", nextConfig.cron?.maxConcurrentRuns ?? 1);
-    setCommandLaneConcurrency(
-      "main",
-      nextConfig.agents?.defaults?.maxConcurrent ?? DEFAULT_AGENT_MAX_CONCURRENT,
-    );
-    setCommandLaneConcurrency(
-      "subagent",
-      nextConfig.agents?.defaults?.subagents?.maxConcurrent ?? DEFAULT_SUBAGENT_MAX_CONCURRENT,
-    );
+    setCommandLaneConcurrency("main", resolveAgentMaxConcurrent(nextConfig));
+    setCommandLaneConcurrency("subagent", resolveSubagentMaxConcurrent(nextConfig));
 
     if (plan.hotReasons.length > 0) {
       params.logReload.info(`config hot reload applied (${plan.hotReasons.join(", ")})`);
diff --git a/src/telegram/monitor.ts b/src/telegram/monitor.ts
index be70c6a337..24c8743df5 100644
--- a/src/telegram/monitor.ts
+++ b/src/telegram/monitor.ts
@@ -1,7 +1,7 @@
 import { type RunOptions, run } from "@grammyjs/runner";
 import type { ClawdbotConfig } from "../config/config.js";
 import { loadConfig } from "../config/config.js";
-import { DEFAULT_AGENT_MAX_CONCURRENT } from "../config/agent-limits.js";
+import { resolveAgentMaxConcurrent } from "../config/agent-limits.js";
 import { computeBackoff, sleepWithAbort } from "../infra/backoff.js";
 import { formatDurationMs } from "../infra/format-duration.js";
 import type { RuntimeEnv } from "../runtime.js";
@@ -29,7 +29,7 @@ export type MonitorTelegramOpts = {
 export function createTelegramRunnerOptions(cfg: ClawdbotConfig): RunOptions<unknown> {
   return {
     sink: {
-      concurrency: cfg.agents?.defaults?.maxConcurrent ?? DEFAULT_AGENT_MAX_CONCURRENT,
+      concurrency: resolveAgentMaxConcurrent(cfg),
     },
     runner: {
       fetch: {