diff --git a/app/(chat)/api/chat/route.ts b/app/(chat)/api/chat/route.ts
index a9b2428674..391faad83e 100644
--- a/app/(chat)/api/chat/route.ts
+++ b/app/(chat)/api/chat/route.ts
@@ -13,6 +13,7 @@ import { createResumableStreamContext } from "resumable-stream";
 import { auth, type UserType } from "@/app/(auth)/auth";
 import { entitlementsByUserType } from "@/lib/ai/entitlements";
 import { type RequestHints, systemPrompt } from "@/lib/ai/prompts";
+import { allowedModelIds } from "@/lib/ai/models";
 import { getLanguageModel } from "@/lib/ai/providers";
 import { createDocument } from "@/lib/ai/tools/create-document";
 import { getWeather } from "@/lib/ai/tools/get-weather";
@@ -74,6 +75,10 @@ export async function POST(request: Request) {
       return new ChatbotError("unauthorized:chat").toResponse();
     }
 
+    if (!allowedModelIds.has(selectedChatModel)) {
+      return new ChatbotError("bad_request:api").toResponse();
+    }
+
     await checkIpRateLimit(ipAddress(request));
 
     const userType: UserType = session.user.type;
@@ -139,8 +144,9 @@ export async function POST(request: Request) {
     }
 
     const isReasoningModel =
-      selectedChatModel.includes("reasoning") ||
-      selectedChatModel.includes("thinking");
+      selectedChatModel.endsWith("-thinking") ||
+      (selectedChatModel.includes("reasoning") &&
+        !selectedChatModel.includes("non-reasoning"));
 
     const modelMessages = await convertToModelMessages(uiMessages);
 
@@ -179,7 +185,9 @@ export async function POST(request: Request) {
           },
         });
 
-        dataStream.merge(result.toUIMessageStream({ sendReasoning: true }));
+        dataStream.merge(
+          result.toUIMessageStream({ sendReasoning: isReasoningModel }),
+        );
 
         if (titlePromise) {
           const title = await titlePromise;
diff --git a/components/message.tsx b/components/message.tsx
index 5ffe67e75d..bc6d268b53 100644
--- a/components/message.tsx
+++ b/components/message.tsx
@@ -110,13 +110,14 @@ const PurePreviewMessage = ({
 
             if (type === "reasoning") {
               const hasContent = part.text?.trim().length > 0;
-              const isStreaming = "state" in part && part.state === "streaming";
-              if (hasContent || isStreaming) {
+              if (hasContent) {
+                const isStreaming =
+                  "state" in part && part.state === "streaming";
                 return (
                   <MessageReasoning
                     isLoading={isLoading || isStreaming}
                     key={key}
-                    reasoning={part.text || ""}
+                    reasoning={part.text}
                   />
                 );
               }
diff --git a/lib/ai/models.ts b/lib/ai/models.ts
index 2241611750..fb5cc70725 100644
--- a/lib/ai/models.ts
+++ b/lib/ai/models.ts
@@ -24,8 +24,8 @@ export const chatModels: ChatModel[] = [
     description: "Fast and cost-effective for simple tasks",
   },
   {
-    id: "openai/gpt-5.2",
-    name: "GPT-5.2",
+    id: "openai/gpt-5-mini",
+    name: "GPT-5 Mini",
     provider: "openai",
     description: "Most capable OpenAI model",
   },
@@ -65,6 +65,8 @@ export const chatModels: ChatModel[] = [
 ];
 
 // Group models by provider for UI
+export const allowedModelIds = new Set(chatModels.map((m) => m.id));
+
 export const modelsByProvider = chatModels.reduce(
   (acc, model) => {
     if (!acc[model.provider]) {
diff --git a/lib/ai/providers.ts b/lib/ai/providers.ts
index 13ba6d3ef6..a93fc8a4b8 100644
--- a/lib/ai/providers.ts
+++ b/lib/ai/providers.ts
@@ -33,7 +33,8 @@ export function getLanguageModel(modelId: string) {
   }
 
   const isReasoningModel =
-    modelId.includes("reasoning") || modelId.endsWith("-thinking");
+    modelId.endsWith("-thinking") ||
+    (modelId.includes("reasoning") && !modelId.includes("non-reasoning"));
 
   if (isReasoningModel) {
     const gatewayModelId = modelId.replace(THINKING_SUFFIX_REGEX, "");