diff --git a/core/llm/llms/OpenAI.ts b/core/llm/llms/OpenAI.ts
index c65b55dc1a5..32288badeaf 100644
--- a/core/llm/llms/OpenAI.ts
+++ b/core/llm/llms/OpenAI.ts
@@ -253,11 +253,18 @@ class OpenAI extends BaseLLM {
   }
 
   protected getMaxStopWords(): number {
-    const url = new URL(this.apiBase!);
-
     if (this.maxStopWords !== undefined) {
       return this.maxStopWords;
-    } else if (url.host === "api.deepseek.com") {
+    }
+
+    // apiBase can legitimately be undefined (e.g. continue-proxy, whose
+    // defaultOptions don't carry one), so guard against `new URL(undefined)`.
+    if (!this.apiBase) {
+      return Infinity;
+    }
+
+    const url = new URL(this.apiBase);
+    if (url.host === "api.deepseek.com") {
       return 16;
     } else if (
       url.port === "1337" ||
diff --git a/core/llm/llms/OpenAI.vitest.ts b/core/llm/llms/OpenAI.vitest.ts
index b07f05b15d8..38450ddbb68 100644
--- a/core/llm/llms/OpenAI.vitest.ts
+++ b/core/llm/llms/OpenAI.vitest.ts
@@ -424,4 +424,31 @@ describe("OpenAI", () => {
       },
     });
   });
+
+  describe("getMaxStopWords", () => {
+    test("returns Infinity instead of throwing when apiBase is undefined", () => {
+      const openai = new OpenAI({
+        apiKey: "test-api-key",
+        model: "gpt-4",
+        apiBase: "https://api.openai.com/v1/",
+      });
+      // continue-proxy and similar providers can leave apiBase undefined
+      (openai as any).apiBase = undefined;
+
+      expect(() => (openai as any).getMaxStopWords()).not.toThrow();
+      expect((openai as any).getMaxStopWords()).toBe(Infinity);
+    });
+
+    test("honors maxStopWords even when apiBase is undefined", () => {
+      const openai = new OpenAI({
+        apiKey: "test-api-key",
+        model: "gpt-4",
+        apiBase: "https://api.openai.com/v1/",
+      });
+      (openai as any).apiBase = undefined;
+      (openai as any).maxStopWords = 7;
+
+      expect((openai as any).getMaxStopWords()).toBe(7);
+    });
+  });
 });