diff --git a/CHANGELOG.md b/CHANGELOG.md
index a25fd8e3bfe..110e55f47d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -108,6 +108,7 @@ Docs: https://docs.openclaw.ai
 - Agents/MCP: sort MCP tools deterministically by name so the tools block in API requests is stable across turns, preventing unnecessary prompt-cache busting from non-deterministic `listTools()` order. (#58037) Thanks @bcherny.
 - Infra/json-file: preserve symlink-backed JSON stores and Windows overwrite fallback when atomically saving small sync JSON state files. (#60589) Thanks @gumadeiras.
 - Matrix/credentials: read the current and legacy credential files directly during migration fallback so concurrent legacy rename races still resolve to the stored credentials. (#60591) Thanks @gumadeiras.
+- Providers/Anthropic Vertex: read ADC files directly during auth discovery so explicit Google credentials and default ADC no longer depend on `existsSync` preflight checks. (#60592) Thanks @gumadeiras.
 
 ## 2026.4.2
 
diff --git a/extensions/anthropic-vertex/region.adc.test.ts b/extensions/anthropic-vertex/region.adc.test.ts
new file mode 100644
index 00000000000..5313a266ced
--- /dev/null
+++ b/extensions/anthropic-vertex/region.adc.test.ts
@@ -0,0 +1,46 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+const { existsSyncMock, readFileSyncMock } = vi.hoisted(() => ({
+  existsSyncMock: vi.fn(),
+  readFileSyncMock: vi.fn(),
+}));
+
+vi.mock("node:fs", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("node:fs")>();
+  existsSyncMock.mockImplementation((pathname) => actual.existsSync(pathname));
+  readFileSyncMock.mockImplementation((pathname, options) =>
+    String(pathname) === "/tmp/vertex-adc.json"
+      ? '{"project_id":"vertex-project"}'
+      : actual.readFileSync(pathname, options as never),
+  );
+  return {
+    ...actual,
+    existsSync: existsSyncMock,
+    readFileSync: readFileSyncMock,
+    default: {
+      ...actual,
+      existsSync: existsSyncMock,
+      readFileSync: readFileSyncMock,
+    },
+  };
+});
+
+import { hasAnthropicVertexAvailableAuth, resolveAnthropicVertexProjectId } from "./region.js";
+
+describe("anthropic-vertex ADC reads", () => {
+  afterEach(() => {
+    existsSyncMock.mockClear();
+    readFileSyncMock.mockClear();
+  });
+
+  it("reads explicit ADC credentials without an existsSync preflight", () => {
+    const env = {
+      GOOGLE_APPLICATION_CREDENTIALS: "/tmp/vertex-adc.json",
+    } as NodeJS.ProcessEnv;
+
+    expect(resolveAnthropicVertexProjectId(env)).toBe("vertex-project");
+    expect(hasAnthropicVertexAvailableAuth(env)).toBe(true);
+    expect(existsSyncMock).not.toHaveBeenCalled();
+    expect(readFileSyncMock).toHaveBeenCalledWith("/tmp/vertex-adc.json", "utf8");
+  });
+});
diff --git a/extensions/anthropic-vertex/region.test.ts b/extensions/anthropic-vertex/region.test.ts
index 6200e5e9753..940ed0fe2c8 100644
--- a/extensions/anthropic-vertex/region.test.ts
+++ b/extensions/anthropic-vertex/region.test.ts
@@ -1,29 +1,38 @@
-import { afterEach, describe, expect, it, vi } from "vitest";
+import { describe, expect, it } from "vitest";
+import { resolveAnthropicVertexRegion, resolveAnthropicVertexRegionFromBaseUrl } from "./api.js";
 
-describe("anthropic-vertex ADC reads", () => {
-  afterEach(() => {
-    vi.resetModules();
-    vi.doUnmock("node:fs");
+describe("anthropic vertex region helpers", () => {
+  it("accepts well-formed regional env values", () => {
+    expect(
+      resolveAnthropicVertexRegion({
+        GOOGLE_CLOUD_LOCATION: "us-east1",
+      } as NodeJS.ProcessEnv),
+    ).toBe("us-east1");
   });
 
-  it("reads explicit ADC credentials without an existsSync preflight", async () => {
-    const existsSync = vi.fn(() => false);
-    const readFileSync = vi.fn((pathname: string) =>
-      pathname.endsWith(".json") ? '{"project_id":"vertex-project"}' : "",
+  it("falls back to the default region for malformed env values", () => {
+    expect(
+      resolveAnthropicVertexRegion({
+        GOOGLE_CLOUD_LOCATION: "us-central1.attacker.example",
+      } as NodeJS.ProcessEnv),
+    ).toBe("global");
+  });
+
+  it("parses regional Vertex endpoints", () => {
+    expect(
+      resolveAnthropicVertexRegionFromBaseUrl("https://europe-west4-aiplatform.googleapis.com"),
+    ).toBe("europe-west4");
+  });
+
+  it("treats the global Vertex endpoint as global", () => {
+    expect(resolveAnthropicVertexRegionFromBaseUrl("https://aiplatform.googleapis.com")).toBe(
+      "global",
     );
-    vi.doMock("node:fs", () => ({
-      existsSync,
-      readFileSync,
-    }));
+  });
 
-    const region = await import("./region.js");
-    const env = {
-      GOOGLE_APPLICATION_CREDENTIALS: "/tmp/vertex-adc.json",
-    } as NodeJS.ProcessEnv;
-
-    expect(region.resolveAnthropicVertexProjectId(env)).toBe("vertex-project");
-    expect(region.hasAnthropicVertexAvailableAuth(env)).toBe(true);
-    expect(existsSync).not.toHaveBeenCalled();
-    expect(readFileSync).toHaveBeenCalledWith("/tmp/vertex-adc.json", "utf8");
+  it("does not infer a Vertex region from custom proxy hosts", () => {
+    expect(
+      resolveAnthropicVertexRegionFromBaseUrl("https://proxy.example.com/google/aiplatform"),
+    ).toBeUndefined();
   });
 });
diff --git a/src/plugin-sdk/anthropic-vertex-auth-presence.preflight.test.ts b/src/plugin-sdk/anthropic-vertex-auth-presence.preflight.test.ts
new file mode 100644
index 00000000000..1d175765695
--- /dev/null
+++ b/src/plugin-sdk/anthropic-vertex-auth-presence.preflight.test.ts
@@ -0,0 +1,45 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+const { existsSyncMock, readFileSyncMock } = vi.hoisted(() => ({
+  existsSyncMock: vi.fn(),
+  readFileSyncMock: vi.fn(),
+}));
+
+vi.mock("node:fs", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("node:fs")>();
+  existsSyncMock.mockImplementation((pathname) => actual.existsSync(pathname));
+  readFileSyncMock.mockImplementation((pathname, options) =>
+    String(pathname) === "/tmp/vertex-adc.json"
+      ? '{"client_id":"vertex-client"}'
+      : actual.readFileSync(pathname, options as never),
+  );
+  return {
+    ...actual,
+    existsSync: existsSyncMock,
+    readFileSync: readFileSyncMock,
+    default: {
+      ...actual,
+      existsSync: existsSyncMock,
+      readFileSync: readFileSyncMock,
+    },
+  };
+});
+
+import { hasAnthropicVertexAvailableAuth } from "./anthropic-vertex-auth-presence.js";
+
+describe("hasAnthropicVertexAvailableAuth ADC preflight", () => {
+  afterEach(() => {
+    existsSyncMock.mockClear();
+    readFileSyncMock.mockClear();
+  });
+
+  it("reads explicit ADC credentials without an existsSync preflight", () => {
+    expect(
+      hasAnthropicVertexAvailableAuth({
+        GOOGLE_APPLICATION_CREDENTIALS: "/tmp/vertex-adc.json",
+      } as NodeJS.ProcessEnv),
+    ).toBe(true);
+    expect(existsSyncMock).not.toHaveBeenCalled();
+    expect(readFileSyncMock).toHaveBeenCalledWith("/tmp/vertex-adc.json", "utf8");
+  });
+});
diff --git a/src/plugin-sdk/anthropic-vertex-auth-presence.ts b/src/plugin-sdk/anthropic-vertex-auth-presence.ts
index 436950da262..6e7bc878b16 100644
--- a/src/plugin-sdk/anthropic-vertex-auth-presence.ts
+++ b/src/plugin-sdk/anthropic-vertex-auth-presence.ts
@@ -1,4 +1,4 @@
-import { existsSync } from "node:fs";
+import { readFileSync } from "node:fs";
 import { homedir, platform } from "node:os";
 import { join } from "node:path";
 import { normalizeOptionalSecretInput } from "../utils/normalize-secret-input.js";
@@ -25,23 +25,31 @@ function resolveAnthropicVertexDefaultAdcPath(env: NodeJS.ProcessEnv = process.e
     : GCLOUD_DEFAULT_ADC_PATH;
 }
 
-function resolveAnthropicVertexAdcCredentialsPath(
+function resolveAnthropicVertexAdcCredentialsPathCandidate(
   env: NodeJS.ProcessEnv = process.env,
 ): string | undefined {
-  const explicitCredentialsPath = env.GOOGLE_APPLICATION_CREDENTIALS?.trim();
+  const explicitCredentialsPath = normalizeOptionalSecretInput(env.GOOGLE_APPLICATION_CREDENTIALS);
   if (explicitCredentialsPath) {
-    return existsSync(explicitCredentialsPath) ? explicitCredentialsPath : undefined;
+    return explicitCredentialsPath;
   }
 
-  const defaultAdcPath = resolveAnthropicVertexDefaultAdcPath(env);
-  return existsSync(defaultAdcPath) ? defaultAdcPath : undefined;
+  return resolveAnthropicVertexDefaultAdcPath(env);
 }
 
-export function hasAnthropicVertexAvailableAuth(
-  env: NodeJS.ProcessEnv = process.env,
-): boolean {
-  return (
-    hasAnthropicVertexMetadataServerAdc(env) ||
-    resolveAnthropicVertexAdcCredentialsPath(env) !== undefined
-  );
+function canReadAnthropicVertexAdc(env: NodeJS.ProcessEnv = process.env): boolean {
+  const credentialsPath = resolveAnthropicVertexAdcCredentialsPathCandidate(env);
+  if (!credentialsPath) {
+    return false;
+  }
+
+  try {
+    readFileSync(credentialsPath, "utf8");
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export function hasAnthropicVertexAvailableAuth(env: NodeJS.ProcessEnv = process.env): boolean {
+  return hasAnthropicVertexMetadataServerAdc(env) || canReadAnthropicVertexAdc(env);
 }