diff --git a/packages/smithy-client/src/exceptions.spec.ts b/packages/smithy-client/src/exceptions.spec.ts
index fc591f96a3e..b82722e0298 100644
--- a/packages/smithy-client/src/exceptions.spec.ts
+++ b/packages/smithy-client/src/exceptions.spec.ts
@@ -34,57 +34,6 @@ it("ExceptionOptionType allows specifying message", () => {
   expect(exception.code).toBe("code");
 });
 
-describe("ServiceException type checking", () => {
-  const error = new ServiceException({
-    name: "Error",
-    $fault: "client",
-    $metadata: {},
-  });
-
-  const duckTyped = {
-    $fault: "server",
-    $metadata: {},
-  };
-
-  describe("isInstance", () => {
-    it("should return true for ServiceException instances", () => {
-      expect(ServiceException.isInstance(error)).toBe(true);
-    });
-
-    it("should return true for duck-typed objects", () => {
-      expect(ServiceException.isInstance(duckTyped)).toBe(true);
-    });
-
-    it("should return false for null or undefined", () => {
-      expect(ServiceException.isInstance(null)).toBe(false);
-      expect(ServiceException.isInstance(undefined)).toBe(false);
-    });
-
-    it("should return false for invalid $fault values", () => {
-      expect(ServiceException.isInstance({ $fault: "invalid", $metadata: {} })).toBe(false);
-    });
-
-    it("should return false for missing properties", () => {
-      expect(ServiceException.isInstance({ $fault: "client" })).toBe(false);
-      expect(ServiceException.isInstance({ $metadata: {} })).toBe(false);
-    });
-  });
-
-  describe("instanceof", () => {
-    it("should return true for ServiceException instances", () => {
-      expect(error instanceof ServiceException).toBe(true);
-    });
-
-    it("should return true for duck-typed objects", () => {
-      expect(duckTyped instanceof ServiceException).toBe(true);
-    });
-
-    it("should return false for invalid objects", () => {
-      expect({} instanceof ServiceException).toBe(false);
-    });
-  });
-});
-
 describe("decorateServiceException", () => {
   const exception = new ServiceException({
     name: "Error",
diff --git a/packages/smithy-client/src/exceptions.ts b/packages/smithy-client/src/exceptions.ts
index 298fd40a65a..8ab84cdaf13 100644
--- a/packages/smithy-client/src/exceptions.ts
+++ b/packages/smithy-client/src/exceptions.ts
@@ -37,23 +37,6 @@ export class ServiceException extends Error implements SmithyException, Metadata
     this.$fault = options.$fault;
     this.$metadata = options.$metadata;
   }
-
-  /**
-   * Checks if a value is an instance of ServiceException (duck typed)
-   */
-  public static isInstance(value: unknown): value is ServiceException {
-    if (!value) return false;
-    const candidate = value as ServiceException;
-    return (
-      Boolean(candidate.$fault) &&
-      Boolean(candidate.$metadata) &&
-      (candidate.$fault === "client" || candidate.$fault === "server")
-    );
-  }
-
-  public static [Symbol.hasInstance](instance: unknown) {
-    return ServiceException.isInstance(instance);
-  }
 }
 
 /**