fix(Basic LLM Chain Node): Use JSON parsing for Claude 3.7 with thinking enabled (n8n-io#15381)

Author: schrothbn

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/methods/chainExecutor.ts

@@ -38,6 +38,18 @@ export function isModelWithResponseFormat(
 	);
 }
 
+export function isModelInThinkingMode(
+	llm: BaseLanguageModel,
+): llm is BaseLanguageModel & { lc_kwargs: { invocationKwargs: { thinking: { type: string } } } } {
+	return (
+		'lc_kwargs' in llm &&
+		'invocationKwargs' in llm.lc_kwargs &&
+		typeof llm.lc_kwargs.invocationKwargs === 'object' &&
+		'thinking' in llm.lc_kwargs.invocationKwargs &&
+		llm.lc_kwargs.invocationKwargs.thinking.type === 'enabled'
+	);
+}
+
 /**
  * Type guard to check if the LLM has a format property(Ollama)
  */
@@ -61,6 +73,10 @@ export function getOutputParserForLLM(
 		return new NaiveJsonOutputParser();
 	}
 
+	if (isModelInThinkingMode(llm)) {
+		return new NaiveJsonOutputParser();
+	}
+
 	return new StringOutputParser();
 }
 

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/test/chainExecutor.test.ts

@@ -62,6 +62,20 @@ describe('chainExecutor', () => {
 			const parser = chainExecutor.getOutputParserForLLM(regularModel);
 			expect(parser).toBeInstanceOf(StringOutputParser);
 		});
+
+		it('should return NaiveJsonOutputParser for Anthropic models in thinking mode', () => {
+			const model = {
+				lc_kwargs: {
+					invocationKwargs: {
+						thinking: {
+							type: 'enabled',
+						},
+					},
+				},
+			};
+			const parser = chainExecutor.getOutputParserForLLM(model as unknown as BaseChatModel);
+			expect(parser).toBeInstanceOf(NaiveJsonOutputParser);
+		});
 	});
 
 	describe('NaiveJsonOutputParser', () => {