diff --git a/.env.example b/.env.example
index bcdd756..ae9658c 100644
--- a/.env.example
+++ b/.env.example
@@ -26,8 +26,12 @@ OPENAI_API_KEY=sk-...
 AI_GATEWAY_API_KEY=
 # Direct Anthropic fallback when gateway auth is not configured
 ANTHROPIC_API_KEY=sk-ant-...
-# Optional override for analysis + scaffold (default: Claude Sonnet 4.5 snapshot)
-# ANTHROPIC_ANALYSIS_MODEL=claude-sonnet-4-5-20250929
+# Optional gateway model override for analysis + scaffold/build (default: anthropic/claude-sonnet-4.6)
+# ANTHROPIC_ANALYSIS_MODEL=anthropic/claude-sonnet-4.6
+# Optional comma-separated fallback models tried by Vercel AI Gateway if the primary model fails
+# AI_GATEWAY_FALLBACK_MODELS=openai/gpt-5.4,anthropic/claude-haiku-4.5,google/gemini-3-flash
+# Optional direct Anthropic model used when falling back from blocked gateway credits
+# ANTHROPIC_DIRECT_MODEL=claude-sonnet-4-5-20250929
 
 # Stripe Billing (set STRIPE_MODE=live for production keys)
 STRIPE_MODE=live
diff --git a/lib/ai-gateway.ts b/lib/ai-gateway.ts
index 629874a..6e58953 100644
--- a/lib/ai-gateway.ts
+++ b/lib/ai-gateway.ts
@@ -3,6 +3,12 @@ import { generateText, type ModelMessage } from 'ai'
 
 /** Default gateway model (provider/model). See https://ai-gateway.vercel.sh/v1/models */
 export const DEFAULT_GATEWAY_MODEL = 'anthropic/claude-sonnet-4.6'
+export const DEFAULT_GATEWAY_FALLBACK_MODELS = [
+  'openai/gpt-5.4',
+  'anthropic/claude-haiku-4.5',
+  'google/gemini-3-flash',
+]
+export const DEFAULT_DIRECT_ANTHROPIC_MODEL = 'claude-sonnet-4-5-20250929'
 
 export type AiGatewayFeature =
   | 'analysis-run'
@@ -23,6 +29,17 @@ function directAnthropicKey(): string | undefined {
   return process.env[ANTHROPIC_KEY_ENV]?.trim()
 }
 
+function parseModelList(value: string | undefined): string[] {
+  return (value ?? '')
+    .split(',')
+    .map((model) => model.trim())
+    .filter(Boolean)
+}
+
+function uniqueModels(models: string[]): string[] {
+  return Array.from(new Set(models))
+}
+
 /** True when AI Gateway or a direct Anthropic key is available. */
 export function isAiConfigured(): boolean {
   return usesGatewayAuth() || Boolean(directAnthropicKey())
@@ -38,6 +55,18 @@ export function getGatewayModel(): string {
   return `anthropic/${configured}`
 }
 
+export function getGatewayFallbackModels(): string[] {
+  const configured = parseModelList(process.env.AI_GATEWAY_FALLBACK_MODELS)
+  const primaryModel = getGatewayModel()
+  const fallbackModels = configured.length > 0 ? configured : DEFAULT_GATEWAY_FALLBACK_MODELS
+
+  return uniqueModels(fallbackModels).filter((model) => model !== primaryModel)
+}
+
+function getDirectAnthropicModel(): string {
+  return process.env.ANTHROPIC_DIRECT_MODEL?.trim() || DEFAULT_DIRECT_ANTHROPIC_MODEL
+}
+
 /**
  * Model id for Anthropic Messages API (gateway-compatible endpoint or direct Anthropic).
  */
@@ -54,6 +83,7 @@ export function getAnthropicMessagesModel(): string {
 
 export function gatewayProviderOptions(userId?: string, feature?: AiGatewayFeature) {
   const tags = feature ? [`feature:${feature}`] : []
+  const fallbackModels = getGatewayFallbackModels()
   if (process.env.VERCEL_ENV) {
     tags.push(`env:${process.env.VERCEL_ENV}`)
   }
@@ -63,6 +93,7 @@ export function gatewayProviderOptions(userId?: string, feature?: AiGatewayFeatu
       gateway: {
         ...(userId ? { user: userId } : {}),
         ...(tags.length > 0 ? { tags } : {}),
+        ...(usesGatewayAuth() && fallbackModels.length > 0 ? { models: fallbackModels } : {}),
       },
     },
   } as const
@@ -87,6 +118,55 @@ export function getAnthropicClient(): Anthropic {
   return new Anthropic({ apiKey: directKey })
 }
 
+function isGatewayAccessError(error: unknown): boolean {
+  const message = error instanceof Error ? error.message : String(error)
+  const lower = message.toLowerCase()
+
+  return (
+    lower.includes('free tier users do not have access') ||
+    lower.includes('upgrade to paid credits') ||
+    lower.includes('top-up') ||
+    lower.includes('payment required') ||
+    lower.includes('insufficient credits') ||
+    lower.includes('gateway credits') ||
+    lower.includes('status code: 402') ||
+    lower.includes('status code: 403')
+  )
+}
+
+async function generateWithDirectAnthropic(params: {
+  system?: string
+  messages: Array<{ role: 'user' | 'assistant'; content: string }>
+  maxOutputTokens?: number
+  temperature?: number
+}): Promise<string> {
+  const directKey = directAnthropicKey()
+  if (!directKey) {
+    throw new Error('Direct Anthropic fallback is not configured.')
+  }
+
+  const client = new Anthropic({ apiKey: directKey })
+  const response = await client.messages.create({
+    model: getDirectAnthropicModel(),
+    max_tokens: params.maxOutputTokens ?? 4096,
+    ...(params.temperature !== undefined ? { temperature: params.temperature } : {}),
+    ...(params.system ? { system: params.system } : {}),
+    messages: params.messages.map((message) => ({
+      role: message.role,
+      content: message.content,
+    })),
+  })
+
+  return response.content
+    .map((block) => (block.type === 'text' ? block.text : ''))
+    .join('')
+    .trim()
+}
+
+function gatewayAccessErrorMessage(): string {
+  return 'AI generation is temporarily unavailable because the configured Vercel AI Gateway account is blocked by model credits. Your Pro app access is active; please contact support or try again shortly.'
+}
+
 export async function generateWithGateway(params: {
   system?: string
   messages: Array<{ role: 'user' | 'assistant'; content: string }>
@@ -100,16 +180,44 @@ export async function generateWithGateway(params: {
     content: message.content,
   }))
 
-  const result = await generateText({
-    model: getGatewayModel(),
-    system: params.system,
-    messages: modelMessages,
-    maxOutputTokens: params.maxOutputTokens ?? 4096,
-    temperature: params.temperature,
-    ...gatewayProviderOptions(params.userId, params.feature),
-  })
+  if (!usesGatewayAuth() && directAnthropicKey()) {
+    return generateWithDirectAnthropic({
+      system: params.system,
+      messages: params.messages,
+      maxOutputTokens: params.maxOutputTokens,
+      temperature: params.temperature,
+    })
+  }
+
+  try {
+    const result = await generateText({
+      model: getGatewayModel(),
+      system: params.system,
+      messages: modelMessages,
+      maxOutputTokens: params.maxOutputTokens ?? 4096,
+      temperature: params.temperature,
+      ...gatewayProviderOptions(params.userId, params.feature),
+    })
+
+    return result.text
+  } catch (error) {
+    if (usesGatewayAuth() && isGatewayAccessError(error)) {
+      const directKey = directAnthropicKey()
+      if (directKey) {
+        console.warn('[ai] Vercel AI Gateway access failed; retrying with direct Anthropic fallback.')
+        return generateWithDirectAnthropic({
+          system: params.system,
+          messages: params.messages,
+          maxOutputTokens: params.maxOutputTokens,
+          temperature: params.temperature,
+        })
+      }
+
+      throw new Error(gatewayAccessErrorMessage())
+    }
 
-  return result.text
+    throw error
+  }
 }
 
 export function aiConfigErrorMessage(): string {