diff --git a/packages/types/src/model.ts b/packages/types/src/model.ts
index 705f17039ec..f7192dd7969 100644
--- a/packages/types/src/model.ts
+++ b/packages/types/src/model.ts
@@ -80,6 +80,8 @@ export const modelInfoSchema = z.object({
 	cachableFields: z.array(z.string()).optional(),
 	// Flag to indicate if the model is deprecated and should not be used
 	deprecated: z.boolean().optional(),
+	// Performance warning message to display when this model is selected
+	performanceWarning: z.string().optional(),
 	// Flag to indicate if the model is free (no cost)
 	isFree: z.boolean().optional(),
 	/**
diff --git a/packages/types/src/providers/openai.ts b/packages/types/src/providers/openai.ts
index a3eed1b57ce..f06f2729b09 100644
--- a/packages/types/src/providers/openai.ts
+++ b/packages/types/src/providers/openai.ts
@@ -81,6 +81,8 @@ export const openAiNativeModels = {
 		outputPrice: 10.0,
 		cacheReadsPrice: 0.13,
 		description: "GPT-5-Codex: A version of GPT-5 optimized for agentic coding in Codex",
+		performanceWarning:
+			"GPT-5-Codex performs poorly with Roo's tool call functionality. Consider using standard GPT-5 models instead for better performance.",
 		supportsVerbosity: true,
 		supportsTemperature: false,
 	},
diff --git a/webview-ui/src/components/settings/ApiOptions.tsx b/webview-ui/src/components/settings/ApiOptions.tsx
index e2e7ba56157..1deb8ff8d6c 100644
--- a/webview-ui/src/components/settings/ApiOptions.tsx
+++ b/webview-ui/src/components/settings/ApiOptions.tsx
@@ -741,6 +741,11 @@ const ApiOptions = ({
 						<ApiErrorMessage errorMessage={t("settings:validation.modelDeprecated")} />
 					)}
 
+					{/* Show performance warning if model has one */}
+					{selectedModelInfo?.performanceWarning && !selectedModelInfo.deprecated && (
+						<ApiErrorMessage errorMessage={selectedModelInfo.performanceWarning} />
+					)}
+
 					{selectedProvider === "bedrock" && selectedModelId === "custom-arn" && (
 						<BedrockCustomArn
 							apiConfiguration={apiConfiguration}
diff --git a/webview-ui/src/components/settings/ModelPicker.tsx b/webview-ui/src/components/settings/ModelPicker.tsx
index 6020a260bd3..522c50c8086 100644
--- a/webview-ui/src/components/settings/ModelPicker.tsx
+++ b/webview-ui/src/components/settings/ModelPicker.tsx
@@ -246,6 +246,9 @@ export const ModelPicker = ({
 			{selectedModelInfo?.deprecated && (
 				<ApiErrorMessage errorMessage={t("settings:validation.modelDeprecated")} />
 			)}
+			{selectedModelInfo?.performanceWarning && !selectedModelInfo.deprecated && (
+				<ApiErrorMessage errorMessage={selectedModelInfo.performanceWarning} />
+			)}
 			{selectedModelId && selectedModelInfo && !selectedModelInfo.deprecated && (
 				<ModelInfoView
 					apiProvider={apiConfiguration.apiProvider}