@@ -5,23 +5,21 @@ import { isFree } from '@/lib/billing/plan-helpers'
 import type { UsageUpgradePayer } from '@/lib/billing/usage-upgrade'
 import { isBillingEnabled, isHosted } from '@/lib/core/config/env-flags'
 
-const logger = createLogger('ChatAccess')
+const logger = createLogger('PaidAccess')
 
 /**
- * Whether a payer may use Chat (talking to Sim). Every turn spends hosted model credits, so a
- * hosted deployment that bills withholds Chat from a payer on the free plan — unless that payer
- * holds prepaid credits, which an admin grants to customers billed outside a subscription.
+ * Whether a payer may use a feature a hosted deployment reserves for paying payers: Chat, and
+ * hosted keys a tool marks `requiresPaidPlan`. A hosted deployment that bills withholds these from
+ * a payer on the free plan, unless that payer holds prepaid credits, which an admin grants to
+ * customers billed outside a subscription.
  *
  * The plan is the payer's entitled subscription (active or past due), so a canceled
  * plan reads as free; a blocked payer is refused by the usage check every caller runs next.
  *
- * This is the single verdict behind every Chat plan gate: run admission, chat titles, scheduled
- * job dispatch, Copilot key admission, and the workspace host context the composer reads, so the
- * composer never offers a send that admission will refuse. A balance that cannot be read admits
- * the payer: a database blip must not lock a paying customer out, and a free payer stays bounded
- * by its usage limit.
+ * A balance that cannot be read admits the payer: a database blip must not lock a paying
+ * customer out, and a free payer stays bounded by its usage limit.
  */
-export async function payerHasChatAccess(payer: UsageUpgradePayer): Promise<boolean> {
+export async function payerHasPaidAccess(payer: UsageUpgradePayer): Promise<boolean> {
   if (!isHosted || !isBillingEnabled) return true
   if (!isFree(payer.payerSubscription?.plan)) return true
   try {
@@ -31,10 +29,20 @@ export async function payerHasChatAccess(payer: UsageUpgradePayer): Promise<bool
     )
     return balance > 0
   } catch (error) {
-    logger.warn('Credit balance unavailable; admitting the payer to Chat', {
+    logger.warn('Credit balance unavailable; admitting the payer', {
       billingEntity: payer.billingEntity,
       error: getErrorMessage(error),
     })
     return true
   }
 }
+
+/**
+ * Whether a payer may use Chat (talking to Sim): {@link payerHasPaidAccess}, since every turn
+ * spends hosted model credits.
+ *
+ * This is the single verdict behind every Chat plan gate: run admission, chat titles, scheduled
+ * job dispatch, Copilot key admission, and the workspace host context the composer reads, so the
+ * composer never offers a send that admission will refuse.
+ */
+export const payerHasChatAccess = payerHasPaidAccess
@@ -17,6 +17,19 @@ export class HostedKeyRateLimitedError extends HttpError {
   }
 }
 
+/**
+ * The tool's hosted key is reserved for paying payers and this run's payer is on the free plan.
+ * Carries a 402 so the run fails as the caller's plan, not as a Sim fault.
+ */
+export class HostedKeyRequiresPaidPlanError extends HttpError {
+  readonly statusCode = 402
+
+  constructor(message: string) {
+    super(message)
+    this.name = 'HostedKeyRequiresPaidPlanError'
+  }
+}
+
 /** No hosted keys are configured or available for this provider. */
 export class HostedKeyUnavailableError extends HttpError {
   readonly statusCode = 503
 
@@ -111,7 +111,9 @@ const {
   mockExecuteChatFunction,
   mockGetInternalToolOperationHandler,
   mockExecuteInternalToolOperation,
+  mockPayerHasPaidAccess,
 } = vi.hoisted(() => ({
+  mockPayerHasPaidAccess: vi.fn(),
   mockGetToolAsync: vi.fn(),
   mockRateLimiterFns: {
     acquireKey: vi.fn(),
@@ -173,6 +175,10 @@ vi.mock('@/lib/core/rate-limiter/hosted-key', () => ({
   getHostedKeyRateLimiter: () => mockRateLimiterFns,
 }))
 
+vi.mock('@/lib/billing/core/chat-access', () => ({
+  payerHasPaidAccess: mockPayerHasPaidAccess,
+}))
+
 vi.mock('@/lib/uploads/contexts/workspace/file-manager', () => workspaceFileManagerMock)
 
 vi.mock(
@@ -6551,6 +6557,97 @@ describe('Hosted Key Injection', () => {
     }
   })
 
+  describe('requiresPaidPlan', () => {
+    const PAID_ONLY_TOOL_ID = 'test_paid_only_hosting'
+
+    beforeEach(() => {
+      setEnvFlags({ isHosted: true, isBillingEnabled: true })
+      mockRateLimiterFns.acquireKey.mockResolvedValue({
+        success: true,
+        key: 'platform-fixture-key',
+        keyIndex: 0,
+        envVarName: 'TEST_HOSTED_KEY',
+      })
+      tools[PAID_ONLY_TOOL_ID] = {
+        id: PAID_ONLY_TOOL_ID,
+        name: 'Paid-only fixture',
+        description: 'Hosted key reserved for paying payers',
+        version: '1.0.0',
+        params: {},
+        request: { url: 'https://example.com/fixture', method: 'GET', headers: () => ({}) },
+        hosting: {
+          envKeyPrefix: 'TEST_HOSTED_KEY',
+          apiKeyParam: 'apiKey',
+          byokProviderId: 'falai',
+          requiresPaidPlan: true,
+          pricing: { type: 'per_request', cost: 0.5 },
+          rateLimit: { mode: 'per_request', requestsPerMinute: 100 },
+        },
+        transformResponse: async () => ({ success: true, output: {} }),
+      }
+    })
+
+    afterEach(() => {
+      Reflect.deleteProperty(tools, PAID_ONLY_TOOL_ID)
+      resetEnvFlagsMock()
+    })
+
+    async function runPaidOnlyTool() {
+      mockValidateUrlWithDNS.mockResolvedValue({ isValid: true, resolvedIP: '93.184.216.34' })
+      mockSecureFetchWithPinnedIP.mockResolvedValue({
+        ok: true,
+        status: 200,
+        statusText: 'OK',
+        headers: { get: () => null, toRecord: () => ({}) },
+        json: async () => ({ ok: true }),
+        text: async () => '{"ok":true}',
+      })
+      const request = mockSecureFetchWithPinnedIP
+      const result = await executeTool(
+        PAID_ONLY_TOOL_ID,
+        {},
+        { executionContext: createToolExecutionContext({ userId: 'user-1' }) }
+      )
+      return { result, request }
+    }
+
+    it('refuses the hosted key to a payer without paid access before acquiring one', async () => {
+      mockGetBYOKKey.mockResolvedValue(null)
+      mockPayerHasPaidAccess.mockResolvedValue(false)
+
+      const { result, request } = await runPaidOnlyTool()
+
+      expect(result.success).toBe(false)
+      expect(result.error).toContain('available on paid plans')
+      expect(mockPayerHasPaidAccess).toHaveBeenCalledWith(TEST_BILLING_ATTRIBUTION)
+      expect(mockRateLimiterFns.acquireKey).not.toHaveBeenCalled()
+      expect(request).not.toHaveBeenCalled()
+    })
+
+    it('grants the hosted key to a payer with paid access', async () => {
+      mockGetBYOKKey.mockResolvedValue(null)
+      mockPayerHasPaidAccess.mockResolvedValue(true)
+
+      const { result, request } = await runPaidOnlyTool()
+
+      expect(result.success).toBe(true)
+      expect(mockRateLimiterFns.acquireKey).toHaveBeenCalledTimes(1)
+      expect(request).toHaveBeenCalledTimes(1)
+    })
+
+    it("runs a free payer's own workspace key without consulting the plan", async () => {
+      mockGetBYOKKey.mockResolvedValue({ apiKey: 'workspace-own-key' })
+      mockPayerHasPaidAccess.mockResolvedValue(false)
+
+      const { result, request } = await runPaidOnlyTool()
+
+      expect(result.success).toBe(true)
+      expect(mockPayerHasPaidAccess).not.toHaveBeenCalled()
+      expect(mockRateLimiterFns.acquireKey).not.toHaveBeenCalled()
+      expect(request).toHaveBeenCalledTimes(1)
+    })
+  })
+
   it('should not inject hosted key when tool has no hosting config', async () => {
     const mockTool = {
       id: 'test_no_hosting',
 
@@ -13,9 +13,12 @@ import type { InternalSandboxProfile } from '@/lib/auth/internal'
 import {
   BILLING_ATTRIBUTION_HEADER,
   type BillingAttributionSnapshot,
+  resolveWorkspaceBillingPayer,
   serializeBillingAttributionHeader,
 } from '@/lib/billing/core/attribution'
-import { isHosted } from '@/lib/core/config/env-flags'
+import { payerHasPaidAccess } from '@/lib/billing/core/chat-access'
+import type { UsageUpgradePayer } from '@/lib/billing/usage-upgrade'
+import { isBillingEnabled, isHosted } from '@/lib/core/config/env-flags'
 import {
   findDatabaseQueryError,
   getUserFacingErrorMessage,
@@ -111,7 +114,11 @@ import {
 } from '@/executor/utils/resolved-secret-trace-registry'
 import type { ErrorInfo } from '@/tools/error-extractors'
 import { extractErrorMessage, redactErrorData } from '@/tools/error-extractors'
-import { HostedKeyRateLimitedError, HostedKeyUnavailableError } from '@/tools/errors'
+import {
+  HostedKeyRateLimitedError,
+  HostedKeyRequiresPaidPlanError,
+  HostedKeyUnavailableError,
+} from '@/tools/errors'
 import {
   getOwnEnumerableDataEntries,
   prepareToolRequest,
@@ -547,6 +554,40 @@ async function registerAssistantCredentialSecrets(
   }
 }
 
+/**
+ * Refuses a `requiresPaidPlan` hosted key to a run whose payer lacks paid access. The payer is
+ * the run's admitted attribution, or the workspace's payer for a surface that carries none; a
+ * workspace without a payer is refused.
+ */
+async function assertPayerMayUseHostedKey(
+  tool: ToolDefinition,
+  workspaceId: string | undefined,
+  billingAttribution: BillingAttributionSnapshot | undefined
+): Promise<void> {
+  if (!isBillingEnabled) return
+
+  let payer: UsageUpgradePayer | null = billingAttribution ?? null
+  if (!payer && workspaceId) {
+    const workspacePayer = await resolveWorkspaceBillingPayer(workspaceId, {
+      onMissing: 'return-null',
+    })
+    if (workspacePayer) {
+      payer = {
+        billingEntity: workspacePayer.organizationId
+          ? { type: 'organization', id: workspacePayer.organizationId }
+          : { type: 'user', id: workspacePayer.billedAccountUserId },
+        payerSubscription: workspacePayer.payerSubscription,
+      }
+    }
+  }
+
+  if (payer && (await payerHasPaidAccess(payer))) return
+
+  throw new HostedKeyRequiresPaidPlanError(
+    `${tool.name} with Sim's hosted key is available on paid plans. Upgrade your plan, or add your own API key under Settings > BYOK.`
+  )
+}
+
 /** Result from hosted key injection */
 interface HostedKeyInjectionResult {
   isUsingHostedKey: boolean
@@ -577,7 +618,10 @@ async function injectHostedKeyIfNeeded(
     return { isUsingHostedKey: false }
   }
 
-  const { workspaceId, userId, workflowId } = resolveToolScope(params, executionContext)
+  const { workspaceId, userId, workflowId, billingAttribution } = resolveToolScope(
+    params,
+    executionContext
+  )
 
   if (byokProviderId && workspaceId) {
     const byokResult = await getBYOKKey(workspaceId, byokProviderId as BYOKProviderId, { signal })
@@ -588,6 +632,10 @@ async function injectHostedKeyIfNeeded(
     }
   }
 
+  if (tool.hosting.requiresPaidPlan) {
+    await assertPayerMayUseHostedKey(tool, workspaceId, billingAttribution)
+  }
+
   const rateLimiter = getHostedKeyRateLimiter()
   const provider = byokProviderId || tool.id
   const billingActorId = workspaceId
 
@@ -499,6 +499,11 @@ export interface ToolHostingConfig<P = Record<string, unknown>> {
   apiKeyParam: string
   /** BYOK provider ID for workspace key lookup */
   byokProviderId?: BYOKProviderId
+  /**
+   * Withholds the hosted key from a free-plan payer without prepaid credits. A workspace BYOK key
+   * or a key the user passes still runs; only Sim's own key is refused.
+   */
+  requiresPaidPlan?: boolean
   /** Pricing when using hosted key */
   pricing: ToolHostingPricing<P>
   /** Hosted key rate limit configuration (required for hosted key distribution) */
 
@@ -71,6 +71,7 @@ export const falaiVideoTool: InternalToolConfig<VideoParams, VideoResponse> = {
     envKeyPrefix: 'FALAI_API_KEY',
     apiKeyParam: 'apiKey',
     byokProviderId: 'falai',
+    requiresPaidPlan: true,
     pricing: {
       type: 'custom',
       getCost: (_params, output) => {