diff --git a/core/llm/llms/Anthropic.ts b/core/llm/llms/Anthropic.ts
index a1fdfbe359..35e9845edd 100644
--- a/core/llm/llms/Anthropic.ts
+++ b/core/llm/llms/Anthropic.ts
@@ -426,6 +426,7 @@ class Anthropic extends BaseLLM {
     const headers = getAnthropicHeaders(
       this.apiKey,
       shouldCacheSystemMessage || shouldCachePrompt,
+      this.apiBase,
     );
 
     const body: MessageCreateParams = {
diff --git a/packages/openai-adapters/src/apis/Anthropic.ts b/packages/openai-adapters/src/apis/Anthropic.ts
index 66656957a1..6b601b424d 100644
--- a/packages/openai-adapters/src/apis/Anthropic.ts
+++ b/packages/openai-adapters/src/apis/Anthropic.ts
@@ -456,7 +456,7 @@ export class AnthropicApi implements BaseLlmApi {
 
   private getHeaders(): Record<string, string> {
     const enableCaching = this.config?.cachingStrategy !== "none";
-    return getAnthropicHeaders(this.config.apiKey, enableCaching);
+    return getAnthropicHeaders(this.config.apiKey, enableCaching, this.apiBase);
   }
 
   async completionNonStream(
diff --git a/packages/openai-adapters/src/apis/AnthropicUtils.test.ts b/packages/openai-adapters/src/apis/AnthropicUtils.test.ts
new file mode 100644
index 0000000000..7ed572c805
--- /dev/null
+++ b/packages/openai-adapters/src/apis/AnthropicUtils.test.ts
@@ -0,0 +1,193 @@
+import { vi } from "vitest";
+import {
+  getAnthropicHeaders,
+  isAzureAnthropicEndpoint,
+} from "./AnthropicUtils.js";
+
+describe("isAzureAnthropicEndpoint", () => {
+  describe("should return true for Azure endpoints", () => {
+    it("detects Azure AI Foundry endpoint", () => {
+      expect(
+        isAzureAnthropicEndpoint(
+          "https://my-resource.services.ai.azure.com/anthropic",
+        ),
+      ).toBe(true);
+    });
+
+    it("detects Azure Cognitive Services endpoint", () => {
+      expect(
+        isAzureAnthropicEndpoint(
+          "https://my-resource.cognitiveservices.azure.com/anthropic",
+        ),
+      ).toBe(true);
+    });
+
+    it("handles case insensitivity", () => {
+      expect(
+        isAzureAnthropicEndpoint(
+          "https://my-resource.SERVICES.AI.AZURE.COM/anthropic",
+        ),
+      ).toBe(true);
+    });
+
+    it("handles mixed case", () => {
+      expect(
+        isAzureAnthropicEndpoint(
+          "https://My-Resource.Services.AI.Azure.Com/anthropic/v1/messages",
+        ),
+      ).toBe(true);
+    });
+  });
+
+  describe("should return false for non-Azure endpoints", () => {
+    it("returns false for standard Anthropic endpoint", () => {
+      expect(isAzureAnthropicEndpoint("https://api.anthropic.com")).toBe(false);
+    });
+
+    it("returns false for undefined", () => {
+      expect(isAzureAnthropicEndpoint(undefined)).toBe(false);
+    });
+
+    it("returns false for empty string", () => {
+      expect(isAzureAnthropicEndpoint("")).toBe(false);
+    });
+
+    it("returns false for invalid URL", () => {
+      expect(isAzureAnthropicEndpoint("not-a-valid-url")).toBe(false);
+    });
+
+    it("returns false for other providers", () => {
+      expect(isAzureAnthropicEndpoint("https://api.openai.com/v1")).toBe(false);
+    });
+  });
+
+  describe("URL parsing security", () => {
+    it("rejects Azure pattern in path (not hostname)", () => {
+      // This should NOT match - Azure domain is in path, not hostname
+      expect(
+        isAzureAnthropicEndpoint(
+          "https://evil.com/services.ai.azure.com/anthropic",
+        ),
+      ).toBe(false);
+    });
+
+    it("rejects Azure pattern as subdomain of non-Azure domain", () => {
+      expect(
+        isAzureAnthropicEndpoint(
+          "https://services.ai.azure.com.evil.com/anthropic",
+        ),
+      ).toBe(false);
+    });
+  });
+});
+
+describe("getAnthropicHeaders", () => {
+  describe("authentication header", () => {
+    it("uses x-api-key for standard Anthropic endpoint", () => {
+      const headers = getAnthropicHeaders(
+        "test-key",
+        false,
+        "https://api.anthropic.com",
+      );
+      expect(headers["x-api-key"]).toBe("test-key");
+      expect(headers["api-key"]).toBeUndefined();
+    });
+
+    it("uses api-key for Azure AI Foundry endpoint", () => {
+      const headers = getAnthropicHeaders(
+        "azure-key",
+        false,
+        "https://my-resource.services.ai.azure.com/anthropic",
+      );
+      expect(headers["api-key"]).toBe("azure-key");
+      expect(headers["x-api-key"]).toBeUndefined();
+    });
+
+    it("uses api-key for Azure Cognitive Services endpoint", () => {
+      const headers = getAnthropicHeaders(
+        "azure-key",
+        false,
+        "https://my-resource.cognitiveservices.azure.com/anthropic",
+      );
+      expect(headers["api-key"]).toBe("azure-key");
+      expect(headers["x-api-key"]).toBeUndefined();
+    });
+
+    it("uses x-api-key when apiBase is undefined", () => {
+      const headers = getAnthropicHeaders("test-key", false, undefined);
+      expect(headers["x-api-key"]).toBe("test-key");
+      expect(headers["api-key"]).toBeUndefined();
+    });
+  });
+
+  describe("caching headers", () => {
+    it("includes anthropic-beta header when caching is enabled", () => {
+      const headers = getAnthropicHeaders("test-key", true);
+      expect(headers["anthropic-beta"]).toBe("prompt-caching-2024-07-31");
+    });
+
+    it("does not include anthropic-beta header when caching is disabled", () => {
+      const headers = getAnthropicHeaders("test-key", false);
+      expect(headers["anthropic-beta"]).toBeUndefined();
+    });
+
+    it("includes caching header for Azure endpoints too", () => {
+      const headers = getAnthropicHeaders(
+        "azure-key",
+        true,
+        "https://my-resource.services.ai.azure.com/anthropic",
+      );
+      expect(headers["anthropic-beta"]).toBe("prompt-caching-2024-07-31");
+    });
+  });
+
+  describe("standard headers", () => {
+    it("always includes anthropic-version header", () => {
+      const headers = getAnthropicHeaders("test-key", false);
+      expect(headers["anthropic-version"]).toBe("2023-06-01");
+    });
+
+    it("always includes Content-Type and Accept headers", () => {
+      const headers = getAnthropicHeaders("test-key", false);
+      expect(headers["Content-Type"]).toBe("application/json");
+      expect(headers["Accept"]).toBe("application/json");
+    });
+  });
+
+  describe("key/endpoint mismatch warning", () => {
+    it("warns when Azure endpoint is used with Anthropic-style key", () => {
+      const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+      getAnthropicHeaders(
+        "sk-ant-test-key",
+        false,
+        "https://my-resource.services.ai.azure.com/anthropic",
+      );
+      expect(warnSpy).toHaveBeenCalledWith(
+        expect.stringContaining("Azure endpoint detected"),
+      );
+      warnSpy.mockRestore();
+    });
+
+    it("does not warn when Azure endpoint is used with Azure key", () => {
+      const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+      getAnthropicHeaders(
+        "azure-api-key-12345",
+        false,
+        "https://my-resource.services.ai.azure.com/anthropic",
+      );
+      expect(warnSpy).not.toHaveBeenCalled();
+      warnSpy.mockRestore();
+    });
+
+    it("does not warn when standard Anthropic endpoint is used with Anthropic key", () => {
+      const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+      getAnthropicHeaders(
+        "sk-ant-test-key",
+        false,
+        "https://api.anthropic.com",
+      );
+      expect(warnSpy).not.toHaveBeenCalled();
+      warnSpy.mockRestore();
+    });
+  });
+});
diff --git a/packages/openai-adapters/src/apis/AnthropicUtils.ts b/packages/openai-adapters/src/apis/AnthropicUtils.ts
index cc0df5ee01..46b28e5785 100644
--- a/packages/openai-adapters/src/apis/AnthropicUtils.ts
+++ b/packages/openai-adapters/src/apis/AnthropicUtils.ts
@@ -34,15 +34,57 @@ export function getAnthropicErrorMessage(response: ErrorResponse): string {
   }
 }
 
+/**
+ * Detects if the given API base URL is an Azure-hosted Anthropic endpoint.
+ * Azure AI Foundry hosts Anthropic models but requires a different auth header.
+ *
+ * Supported Azure endpoint patterns:
+ * - *.services.ai.azure.com (Azure AI Foundry)
+ * - *.cognitiveservices.azure.com (Azure Cognitive Services)
+ *
+ * @param apiBase - The API base URL to check
+ * @returns true if the endpoint is an Azure-hosted Anthropic endpoint
+ */
+export function isAzureAnthropicEndpoint(apiBase?: string): boolean {
+  if (!apiBase) {
+    return false;
+  }
+
+  try {
+    const url = new URL(apiBase);
+    const hostname = url.hostname.toLowerCase();
+    return (
+      hostname.endsWith(".services.ai.azure.com") ||
+      hostname.endsWith(".cognitiveservices.azure.com")
+    );
+  } catch {
+    // Invalid URL - fall back to false
+    return false;
+  }
+}
+
 export function getAnthropicHeaders(
   apiKey: string,
   enableCaching: boolean,
+  apiBase?: string,
 ): Record<string, string> {
+  const isAzure = isAzureAnthropicEndpoint(apiBase);
+
+  // Warn if Azure endpoint is used with Anthropic-style key
+  if (isAzure && apiKey.startsWith("sk-ant-")) {
+    console.warn(
+      "[Continue] Azure endpoint detected but API key appears to be a standard Anthropic key (sk-ant-*). " +
+        "Azure endpoints require Azure API keys from your AI Foundry resource.",
+    );
+  }
+
+  const authHeaderName = isAzure ? "api-key" : "x-api-key";
+
   const headers: Record<string, string> = {
     "Content-Type": "application/json",
     Accept: "application/json",
     "anthropic-version": "2023-06-01",
-    "x-api-key": apiKey,
+    [authHeaderName]: apiKey,
   };
 
   if (enableCaching) {