diff --git a/packages/types/src/provider-settings.ts b/packages/types/src/provider-settings.ts
index 3b3717ad45..8cad064732 100644
--- a/packages/types/src/provider-settings.ts
+++ b/packages/types/src/provider-settings.ts
@@ -250,6 +250,7 @@ const openAiSchema = baseProviderSettingsSchema.extend({
 	openAiStreamingEnabled: z.boolean().optional(),
 	openAiHostHeader: z.string().optional(), // Keep temporarily for backward compatibility during migration.
 	openAiHeaders: z.record(z.string(), z.string()).optional(),
+	openAiStrictToolMessageOrdering: z.boolean().optional(), // Merge text after tool results to avoid "user after tool" errors.
 })
 
 const ollamaSchema = baseProviderSettingsSchema.extend({
diff --git a/src/api/providers/openai.ts b/src/api/providers/openai.ts
index 43a4fe7ae3..0906e4fd8a 100644
--- a/src/api/providers/openai.ts
+++ b/src/api/providers/openai.ts
@@ -122,7 +122,11 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 					}
 				}
 
-				convertedMessages = [systemMessage, ...convertToOpenAiMessages(messages)]
+				// When openAiStrictToolMessageOrdering is enabled, merge text content after tool results
+				// into the last tool message. This fixes "user after tool" errors with NVIDIA NIM,
+				// OpenRouter, and other strict OpenAI-compatible APIs.
+				const mergeToolResultText = this.options.openAiStrictToolMessageOrdering ?? false
+				convertedMessages = [systemMessage, ...convertToOpenAiMessages(messages, { mergeToolResultText })]
 
 				if (modelInfo.supportsPromptCache) {
 					// Note: the following logic is copied from openrouter:
@@ -224,11 +228,15 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 				yield this.processUsageMetrics(lastUsage, modelInfo)
 			}
 		} else {
+			// When openAiStrictToolMessageOrdering is enabled, merge text content after tool results
+			// into the last tool message. This fixes "user after tool" errors with NVIDIA NIM,
+			// OpenRouter, and other strict OpenAI-compatible APIs.
+			const mergeToolResultText = this.options.openAiStrictToolMessageOrdering ?? false
 			const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsNonStreaming = {
 				model: modelId,
 				messages: deepseekReasoner
 					? convertToR1Format([{ role: "user", content: systemPrompt }, ...messages])
-					: [systemMessage, ...convertToOpenAiMessages(messages)],
+					: [systemMessage, ...convertToOpenAiMessages(messages, { mergeToolResultText })],
 				...(metadata?.tools && { tools: this.convertToolsForOpenAI(metadata.tools) }),
 				...(metadata?.tool_choice && { tool_choice: metadata.tool_choice }),
 				...(metadata?.toolProtocol === "native" && {
@@ -342,6 +350,10 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 		if (this.options.openAiStreamingEnabled ?? true) {
 			const isGrokXAI = this._isGrokXAI(this.options.openAiBaseUrl)
 
+			// When openAiStrictToolMessageOrdering is enabled, merge text content after tool results
+			// into the last tool message. This fixes "user after tool" errors with NVIDIA NIM,
+			// OpenRouter, and other strict OpenAI-compatible APIs.
+			const mergeToolResultText = this.options.openAiStrictToolMessageOrdering ?? false
 			const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsStreaming = {
 				model: modelId,
 				messages: [
@@ -349,7 +361,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 						role: "developer",
 						content: `Formatting re-enabled\n${systemPrompt}`,
 					},
-					...convertToOpenAiMessages(messages),
+					...convertToOpenAiMessages(messages, { mergeToolResultText }),
 				],
 				stream: true,
 				...(isGrokXAI ? {} : { stream_options: { include_usage: true } }),
@@ -379,6 +391,10 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 
 			yield* this.handleStreamResponse(stream)
 		} else {
+			// When openAiStrictToolMessageOrdering is enabled, merge text content after tool results
+			// into the last tool message. This fixes "user after tool" errors with NVIDIA NIM,
+			// OpenRouter, and other strict OpenAI-compatible APIs.
+			const mergeToolResultText = this.options.openAiStrictToolMessageOrdering ?? false
 			const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsNonStreaming = {
 				model: modelId,
 				messages: [
@@ -386,7 +402,7 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 						role: "developer",
 						content: `Formatting re-enabled\n${systemPrompt}`,
 					},
-					...convertToOpenAiMessages(messages),
+					...convertToOpenAiMessages(messages, { mergeToolResultText }),
 				],
 				reasoning_effort: modelInfo.reasoningEffort as "low" | "medium" | "high" | undefined,
 				temperature: undefined,
diff --git a/webview-ui/src/components/settings/providers/OpenAICompatible.tsx b/webview-ui/src/components/settings/providers/OpenAICompatible.tsx
index 4eea6f09f1..25fefd2639 100644
--- a/webview-ui/src/components/settings/providers/OpenAICompatible.tsx
+++ b/webview-ui/src/components/settings/providers/OpenAICompatible.tsx
@@ -158,6 +158,16 @@ export const OpenAICompatible = ({
 				onChange={handleInputChange("openAiStreamingEnabled", noTransform)}>
 				{t("settings:modelInfo.enableStreaming")}
 			</Checkbox>
+			<div>
+				<Checkbox
+					checked={apiConfiguration?.openAiStrictToolMessageOrdering ?? false}
+					onChange={handleInputChange("openAiStrictToolMessageOrdering", noTransform)}>
+					{t("settings:providers.openAiStrictToolMessageOrdering")}
+				</Checkbox>
+				<div className="text-sm text-vscode-descriptionForeground ml-6">
+					{t("settings:providers.openAiStrictToolMessageOrderingDescription")}
+				</div>
+			</div>
 			<div>
 				<Checkbox
 					checked={apiConfiguration?.includeMaxTokens ?? true}
diff --git a/webview-ui/src/i18n/locales/en/settings.json b/webview-ui/src/i18n/locales/en/settings.json
index 17d14da8bd..0b78ee2196 100644
--- a/webview-ui/src/i18n/locales/en/settings.json
+++ b/webview-ui/src/i18n/locales/en/settings.json
@@ -531,7 +531,9 @@
 			"placeholder": "Default: claude",
 			"maxTokensLabel": "Max Output Tokens",
 			"maxTokensDescription": "Maximum number of output tokens for Claude Code responses. Default is 8000."
-		}
+		},
+		"openAiStrictToolMessageOrdering": "Strict tool message ordering",
+		"openAiStrictToolMessageOrderingDescription": "Enable this if your API returns errors like \"Unexpected role 'user' after role 'tool'\". This merges text content into tool messages to fix compatibility with NVIDIA NIM, OpenRouter, and other strict OpenAI-compatible APIs."
 	},
 	"browser": {
 		"enable": {