fix(openai): Allow o1 to stream a single chunk

libs/langchain-openai/src/chat_models.ts

@@ -1002,7 +1002,8 @@ export class ChatOpenAI<
     this.reasoningEffort = fields?.reasoningEffort;
 
     if (this.model === "o1") {
-      this.disableStreaming = true;
+      this.disableStreaming =
+        fields?.disableStreaming != null ? fields?.disableStreaming : true;
     }
 
     this.streaming = fields?.streaming ?? false;
@@ -1310,6 +1311,15 @@ export class ChatOpenAI<
     options: this["ParsedCallOptions"],
     runManager?: CallbackManagerForLLMRun
   ): AsyncGenerator<ChatGenerationChunk> {
+    if (this.streaming === false) {
+      const result = await this._generate(messages, options, runManager);
+      yield new ChatGenerationChunk({
+        message: new AIMessageChunk({ ...result.generations[0].message }),
+        text: result.generations[0].text,
+      });
+      return;
+    }
+
     const messagesMapped: OpenAICompletionParam[] =
       _convertMessagesToOpenAIParams(messages, this.model);
     const params = {
@@ -1320,7 +1330,6 @@ export class ChatOpenAI<
       stream: true as const,
     };
     let defaultRole: OpenAIRoleEnum | undefined;
-
     const streamIterable = await this.completionWithRetry(params, options);
     let usage: OpenAIClient.Completions.CompletionUsage | undefined;
     for await (const data of streamIterable) {

libs/langchain-openai/src/tests/chat_models.int.test.ts

@@ -1285,3 +1285,27 @@ test.skip("Allow overriding", async () => {
     console.log(chunk);
   }
 });
+
+test("Streaming with o1 will yield at least one chunk with content", async () => {
+  const model = new ChatOpenAI({
+    model: "o1",
+    disableStreaming: false,
+    streaming: false,
+  });
+
+  const result = model.streamEvents([["user", "What color is the sky?"]], {
+    version: "v2",
+  });
+
+  let content = "";
+  let numStreamChunks = 0;
+  for await (const chunk of result) {
+    if (chunk.event === "on_chat_model_stream") {
+      content += chunk.data.chunk.content;
+      numStreamChunks += 1;
+    }
+  }
+
+  expect(content.length).toBeGreaterThan(10);
+  expect(numStreamChunks).toBe(1);
+});