diff --git a/apps/web/src/app/admin/gateway/RoutingContent.tsx b/apps/web/src/app/admin/gateway/RoutingContent.tsx
index 0251b8e010d..cb5a24db618 100644
--- a/apps/web/src/app/admin/gateway/RoutingContent.tsx
+++ b/apps/web/src/app/admin/gateway/RoutingContent.tsx
@@ -11,8 +11,10 @@ import { Label } from '@/components/ui/label';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
 import {
   DEFAULT_VERCEL_ROUTING_ENABLED,
+  GatewayConfigInputSchema,
   NOTE_MAX_LENGTH,
 } from '@kilocode/web-shared/lib/ai-gateway/gateway-config';
+import { formatZodError } from '@/lib/zod/format-zod-error';
 
 export function RoutingContent() {
   const trpc = useTRPC();
@@ -24,6 +26,7 @@ export function RoutingContent() {
   const [optOutModelsValue, setOptOutModelsValue] = useState('');
   const [noteValue, setNoteValue] = useState('');
   const [hasChanges, setHasChanges] = useState(false);
+  const [validationError, setValidationError] = useState<string | null>(null);
 
   useEffect(() => {
     if (data) {
@@ -43,7 +46,7 @@ export function RoutingContent() {
         toast.success('Gateway routing configuration updated');
       },
       onError: error => {
-        toast.error(error.message || 'Failed to update');
+        toast.error(formatZodError(error));
       },
     })
   );
@@ -53,23 +56,20 @@ export function RoutingContent() {
     return trimmed === '' ? null : trimmed;
   }
 
-  function optOutModels() {
-    return [
-      ...new Set(
-        optOutModelsValue
-          .split('\n')
-          .map(model => model.trim())
-          .filter(Boolean)
-      ),
-    ];
-  }
-
   function handleSave() {
-    mutation.mutate({
+    const parsed = GatewayConfigInputSchema.safeParse({
       vercel_routing_enabled: vercelEnabled,
-      vercel_routing_opt_out_models: optOutModels(),
+      vercel_routing_opt_out_models: optOutModelsValue
+        .split('\n')
+        .filter(model => model.trim() !== ''),
       note: noteInput(),
     });
+    if (!parsed.success) {
+      setValidationError(formatZodError(parsed.error));
+      return;
+    }
+    setValidationError(null);
+    mutation.mutate(parsed.data);
   }
 
   if (isLoading) {
@@ -108,11 +108,17 @@ export function RoutingContent() {
             <Label htmlFor="routing-opt-out-models">Opt-out models</Label>
             <Textarea
               id="routing-opt-out-models"
-              aria-describedby="routing-opt-out-models-description"
+              aria-describedby={
+                validationError
+                  ? 'routing-opt-out-models-description routing-opt-out-models-error'
+                  : 'routing-opt-out-models-description'
+              }
+              aria-invalid={validationError ? true : undefined}
               placeholder={'moonshotai/kimi-k3\nprovider/another-model'}
               value={optOutModelsValue}
               onChange={e => {
                 setOptOutModelsValue(e.target.value);
+                setValidationError(null);
                 setHasChanges(true);
               }}
               rows={6}
@@ -122,6 +128,15 @@ export function RoutingContent() {
               One model ID per line. Matching is exact after entries are lowercased; matching models
               are never routed to Vercel. Changes take effect within one minute on warm instances.
             </p>
+            {validationError && (
+              <pre
+                id="routing-opt-out-models-error"
+                className="bg-destructive/10 text-destructive rounded-md p-3 text-sm whitespace-pre-wrap"
+                role="alert"
+              >
+                {validationError}
+              </pre>
+            )}
           </div>
 
           <div className="flex flex-col gap-2">
diff --git a/apps/web/src/routers/admin/gateway-config-router.test.ts b/apps/web/src/routers/admin/gateway-config-router.test.ts
new file mode 100644
index 00000000000..ffe5b18927d
--- /dev/null
+++ b/apps/web/src/routers/admin/gateway-config-router.test.ts
@@ -0,0 +1,78 @@
+import { beforeEach, describe, expect, it } from '@jest/globals';
+import { cleanupDbForTest, db } from '@kilocode/web-shared/lib/drizzle';
+import { ai_gateway_config, type User } from '@kilocode/db/schema';
+import { VERCEL_ROUTING_OPT_OUT_MODEL_MAX_LENGTH } from '@kilocode/web-shared/lib/ai-gateway/gateway-config';
+import { insertTestUser } from '@kilocode/web-shared/tests/helpers/user.helper';
+import { createCallerForUser } from '@/routers/test-utils';
+
+let admin: User;
+
+beforeEach(async () => {
+  await cleanupDbForTest();
+  admin = await insertTestUser({
+    google_user_email: `gateway-config-admin-${Math.random()}@admin.example.com`,
+    is_admin: true,
+  });
+});
+
+const input = {
+  vercel_routing_enabled: false,
+  vercel_routing_opt_out_models: [' MoonshotAI/Kimi-K3 ', 'moonshotai/kimi-k3', 'openai/gpt-6'],
+  note: 'Holding opt-outs',
+};
+
+const normalizedOptOutModels = ['moonshotai/kimi-k3', 'openai/gpt-6'];
+
+describe('adminGatewayConfigRouter', () => {
+  it('stores the normalized opt-out list and reads it back', async () => {
+    const caller = await createCallerForUser(admin.id);
+
+    const saved = await caller.admin.gatewayConfig.set(input);
+    expect({
+      vercel_routing_enabled: saved.vercel_routing_enabled,
+      vercel_routing_opt_out_models: saved.vercel_routing_opt_out_models,
+      note: saved.note,
+    }).toEqual({
+      vercel_routing_enabled: false,
+      vercel_routing_opt_out_models: normalizedOptOutModels,
+      note: 'Holding opt-outs',
+    });
+
+    const [row] = await db.select().from(ai_gateway_config);
+    expect(row.config).toMatchObject({
+      vercel_routing_enabled: false,
+      vercel_routing_opt_out_models: normalizedOptOutModels,
+      note: 'Holding opt-outs',
+    });
+
+    await expect(caller.admin.gatewayConfig.get()).resolves.toMatchObject({
+      vercel_routing_enabled: false,
+      vercel_routing_opt_out_models: normalizedOptOutModels,
+      note: 'Holding opt-outs',
+    });
+  });
+
+  it('rejects a blank opt-out entry without writing', async () => {
+    const caller = await createCallerForUser(admin.id);
+
+    await expect(
+      caller.admin.gatewayConfig.set({
+        ...input,
+        vercel_routing_opt_out_models: ['moonshotai/kimi-k3', ''],
+      })
+    ).rejects.toMatchObject({ code: 'BAD_REQUEST' });
+    expect(await db.select().from(ai_gateway_config)).toEqual([]);
+  });
+
+  it('rejects an over-length opt-out entry without writing', async () => {
+    const caller = await createCallerForUser(admin.id);
+
+    await expect(
+      caller.admin.gatewayConfig.set({
+        ...input,
+        vercel_routing_opt_out_models: ['x'.repeat(VERCEL_ROUTING_OPT_OUT_MODEL_MAX_LENGTH + 1)],
+      })
+    ).rejects.toMatchObject({ code: 'BAD_REQUEST' });
+    expect(await db.select().from(ai_gateway_config)).toEqual([]);
+  });
+});
diff --git a/apps/web/src/routers/admin/gateway-config-router.ts b/apps/web/src/routers/admin/gateway-config-router.ts
index 659799eb4c2..25d4d649f18 100644
--- a/apps/web/src/routers/admin/gateway-config-router.ts
+++ b/apps/web/src/routers/admin/gateway-config-router.ts
@@ -29,14 +29,9 @@ export const adminGatewayConfigRouter = createTRPCRouter({
   }),
 
   set: adminProcedure.input(GatewayConfigInputSchema).mutation(async ({ input, ctx }) => {
-    const optOutModels = [
-      ...new Set(
-        input.vercel_routing_opt_out_models.map(model => model.trim().toLowerCase()).filter(Boolean)
-      ),
-    ];
     const config: GatewayConfig = {
       vercel_routing_enabled: input.vercel_routing_enabled,
-      vercel_routing_opt_out_models: optOutModels,
+      vercel_routing_opt_out_models: input.vercel_routing_opt_out_models,
       updated_at: new Date().toISOString(),
       updated_by: ctx.user.id,
       updated_by_email: ctx.user.google_user_email,
diff --git a/packages/web-shared/src/lib/ai-gateway/gateway-config.test.ts b/packages/web-shared/src/lib/ai-gateway/gateway-config.test.ts
index 727336e87b9..8a0dc9386ae 100644
--- a/packages/web-shared/src/lib/ai-gateway/gateway-config.test.ts
+++ b/packages/web-shared/src/lib/ai-gateway/gateway-config.test.ts
@@ -4,6 +4,8 @@ import {
   GatewayConfigSchema,
   GatewayConfigInputSchema,
   NOTE_MAX_LENGTH,
+  VERCEL_ROUTING_OPT_OUT_MODEL_MAX_LENGTH,
+  VERCEL_ROUTING_OPT_OUT_MODELS_MAX_COUNT,
 } from './gateway-config';
 
 describe('GatewayRoutingConfigSchema', () => {
@@ -140,4 +142,89 @@ describe('GatewayConfigInputSchema', () => {
       })
     ).toThrow();
   });
+
+  test.each(['', '   ', '\t'])('rejects the blank opt-out entry %p', entry => {
+    expect(() =>
+      GatewayConfigInputSchema.parse({
+        vercel_routing_enabled: true,
+        vercel_routing_opt_out_models: ['moonshotai/kimi-k3', entry],
+        note: null,
+      })
+    ).toThrow();
+  });
+
+  test('rejects an opt-out entry longer than the maximum', () => {
+    expect(() =>
+      GatewayConfigInputSchema.parse({
+        vercel_routing_enabled: true,
+        vercel_routing_opt_out_models: ['x'.repeat(VERCEL_ROUTING_OPT_OUT_MODEL_MAX_LENGTH + 1)],
+        note: null,
+      })
+    ).toThrow();
+  });
+
+  test('accepts an opt-out entry at the maximum length', () => {
+    const model = 'x'.repeat(VERCEL_ROUTING_OPT_OUT_MODEL_MAX_LENGTH);
+    expect(
+      GatewayConfigInputSchema.parse({
+        vercel_routing_enabled: true,
+        vercel_routing_opt_out_models: [model],
+        note: null,
+      }).vercel_routing_opt_out_models
+    ).toEqual([model]);
+  });
+
+  test('rejects more opt-out entries than the maximum count', () => {
+    const models = Array.from(
+      { length: VERCEL_ROUTING_OPT_OUT_MODELS_MAX_COUNT + 1 },
+      (_, index) => `provider/model-${index}`
+    );
+    expect(() =>
+      GatewayConfigInputSchema.parse({
+        vercel_routing_enabled: true,
+        vercel_routing_opt_out_models: models,
+        note: null,
+      })
+    ).toThrow();
+  });
+
+  test('trims, lowercases, and collapses duplicate opt-out entries', () => {
+    const parsed = GatewayConfigInputSchema.parse({
+      vercel_routing_enabled: true,
+      vercel_routing_opt_out_models: [
+        '  MoonshotAI/Kimi-K3  ',
+        'moonshotai/kimi-k3',
+        'provider/model-b',
+        'PROVIDER/MODEL-B',
+      ],
+      note: null,
+    });
+    expect(parsed.vercel_routing_opt_out_models).toEqual([
+      'moonshotai/kimi-k3',
+      'provider/model-b',
+    ]);
+  });
+
+  test('round-trips an accepted input through the stored-config and hot-path schemas', () => {
+    const input = GatewayConfigInputSchema.parse({
+      vercel_routing_enabled: false,
+      vercel_routing_opt_out_models: [' MoonshotAI/Kimi-K3 ', 'moonshotai/kimi-k3', 'openai/gpt-6'],
+      note: 'Holding opt-outs',
+    });
+    const storedJson = JSON.stringify({
+      vercel_routing_enabled: input.vercel_routing_enabled,
+      vercel_routing_opt_out_models: input.vercel_routing_opt_out_models,
+      updated_at: '2026-01-01T00:00:00.000Z',
+      updated_by: 'u1',
+      updated_by_email: 'a@example.com',
+      note: input.note,
+    });
+
+    expect(GatewayConfigSchema.parse(JSON.parse(storedJson)).vercel_routing_opt_out_models).toEqual(
+      ['moonshotai/kimi-k3', 'openai/gpt-6']
+    );
+    expect(
+      GatewayRoutingConfigSchema.parse(JSON.parse(storedJson)).vercel_routing_opt_out_models
+    ).toEqual(['moonshotai/kimi-k3', 'openai/gpt-6']);
+  });
 });
diff --git a/packages/web-shared/src/lib/ai-gateway/gateway-config.ts b/packages/web-shared/src/lib/ai-gateway/gateway-config.ts
index 2aaa8d31245..8626fb477c9 100644
--- a/packages/web-shared/src/lib/ai-gateway/gateway-config.ts
+++ b/packages/web-shared/src/lib/ai-gateway/gateway-config.ts
@@ -4,6 +4,9 @@ export const DEFAULT_VERCEL_ROUTING_ENABLED = true;
 
 export const NOTE_MAX_LENGTH = 500;
 
+export const VERCEL_ROUTING_OPT_OUT_MODEL_MAX_LENGTH = 200;
+export const VERCEL_ROUTING_OPT_OUT_MODELS_MAX_COUNT = 200;
+
 const note = z.string().max(NOTE_MAX_LENGTH);
 
 /**
@@ -38,9 +41,20 @@ export const GatewayRoutingConfigSchema = z.object({
   vercel_routing_opt_out_models: z.array(z.string().min(1)).default([]),
 });
 
+/**
+ * The admin form submits one model ID per line, so the write schema owns the
+ * stored form: trimmed, lowercase, non-empty, bounded and duplicate-free. Every
+ * accepted input therefore stays parseable by the stored-config and hot-path
+ * schemas, and a saved list never carries an entry the readers reject.
+ */
+const vercelRoutingOptOutModels = z
+  .array(z.string().trim().toLowerCase().min(1).max(VERCEL_ROUTING_OPT_OUT_MODEL_MAX_LENGTH))
+  .max(VERCEL_ROUTING_OPT_OUT_MODELS_MAX_COUNT)
+  .transform(models => [...new Set(models)]);
+
 /** Schema for the admin set-mutation input. */
 export const GatewayConfigInputSchema = z.object({
   vercel_routing_enabled: z.boolean(),
-  vercel_routing_opt_out_models: z.array(z.string()),
+  vercel_routing_opt_out_models: vercelRoutingOptOutModels,
   note: note.nullable(),
 });