Fix issu in gpt-5*, o1*, and o3* models as not supporting stop to avoid 400 Unsupported parameter errors.

packages/components/nodes/agents/ConversationalAgent/ConversationalAgent.ts

@@ -263,10 +263,11 @@ const prepareAgent = async (
         }
     }
 
-    /** Bind a stop token to the model */
-    const modelWithStop = model.bind({
-        stop: ['\nObservation']
-    })
+    /** Bind a stop token to the model if supported */
+    // Avoid passing `stop` to models that reject it (e.g. gpt-5-nano)
+    const { modelSupportsStop } = await import('../../../src/utils')
+    const modelId = (model as any)?.modelName ?? (model as any)?.model ?? (model as any)?.configuredModel
+    const modelWithStop = modelSupportsStop(modelId) ? model.bind({ stop: ['\nObservation'] }) : model
 
     const runnableAgent = RunnableSequence.from([
         {

packages/components/nodes/agents/XMLAgent/XMLAgent.ts

@@ -246,7 +246,11 @@ const prepareAgent = async (
         throw new Error(`Provided prompt is missing required input variables: ${JSON.stringify(missingVariables)}`)
     }
 
-    const llmWithStop = model.bind({ stop: ['</tool_input>', '</final_answer>'] })
+    const { modelSupportsStop } = await import('../../../src/utils')
+    const modelId = (model as any)?.modelName ?? (model as any)?.model ?? (model as any)?.configuredModel
+    const llmWithStop = modelSupportsStop(modelId)
+        ? (model as BaseChatModel).bind({ stop: ['</tool_input>', '</final_answer>'] })
+        : (model as BaseChatModel)
 
     const messages = (await memory.getChatMessages(flowObj.sessionId, false, prependMessages)) as IMessage[]
     let chatHistoryMsgTxt = ''

packages/components/src/agents.ts

@@ -24,6 +24,7 @@ import {
 } from 'langchain/agents'
 import { formatLogToString } from 'langchain/agents/format_scratchpad/log'
 import { IUsedTool } from './Interface'
+import { modelSupportsStop } from './utils'
 import { getErrorMessage } from './error'
 
 export const SOURCE_DOCUMENTS_PREFIX = '\n\n----FLOWISE_SOURCE_DOCUMENTS----\n\n'
@@ -778,9 +779,11 @@ export const createReactAgent = async ({ llm, tools, prompt }: CreateReactAgentP
         tool_names: toolNames.join(', ')
     })
     // TODO: Add .bind to core runnable interface.
-    const llmWithStop = (llm as BaseLanguageModel).bind({
-        stop: ['\nObservation:']
-    })
+    // Bind stop only when the underlying model supports it (some models like gpt-5-nano reject `stop`)
+    const llmModelName = (llm as any)?.modelName ?? (llm as any)?.model ?? (llm as any)?.configuredModel
+    const llmWithStop = modelSupportsStop(llmModelName)
+        ? (llm as BaseLanguageModel).bind({ stop: ['\nObservation:'] })
+        : (llm as BaseLanguageModel)
     const agent = RunnableSequence.from([
         RunnablePassthrough.assign({
             //@ts-ignore

packages/components/src/utils.ts

@@ -138,6 +138,21 @@ export const defaultAllowBuiltInDep = [
     'zlib'
 ]
 
+/**
+ * Return true if the model name likely supports the `stop` parameter.
+ * Some newer OpenAI models (for example gpt-5-nano) do not accept the `stop` parameter
+ * and will return an HTTP 400 when it is provided. Add model names here as needed.
+ */
+export const modelSupportsStop = (modelName?: string): boolean => {
+    if (!modelName) return true
+    const lower = modelName.toLowerCase()
+    // Treat all gpt-5*, o1*, and o3* models as not supporting `stop`
+    // to avoid 400 Unsupported parameter errors.
+    const unsupportedPrefixes = ['gpt-5', 'o1', 'o3']
+    if (unsupportedPrefixes.some((prefix) => lower.startsWith(prefix))) return false
+    return true
+}
+
 /**
  * Get base classes of components
  *