diff --git a/apps/sim/lib/core/config/env-flags.dom.test.ts b/apps/sim/lib/core/config/env-flags.dom.test.ts
new file mode 100644
index 00000000000..3511aaccf2b
--- /dev/null
+++ b/apps/sim/lib/core/config/env-flags.dom.test.ts
@@ -0,0 +1,54 @@
+/**
+ * @vitest-environment jsdom
+ * @vitest-environment-options {"url":"https://www.sim.ai"}
+ */
+import { afterEach, describe, expect, it, vi } from 'vitest'
+
+vi.hoisted(() => {
+  vi.stubEnv('NEXT_PUBLIC_APP_URL', '')
+  vi.stubEnv('NEXT_PUBLIC_FORCE_HOSTED', 'false')
+  vi.stubEnv('NODE_ENV', 'production')
+  document.documentElement.id = '__next_error__'
+})
+
+vi.unmock('@/lib/core/config/env')
+vi.unmock('@/lib/core/config/env-flags')
+vi.mock('@/lib/oauth/utils', () => ({ getScopesForService: () => [] }))
+vi.mock('@/providers/utils', () => ({ getProviderFromModel: () => 'openai' }))
+
+import { getEnv, PUBLIC_ENV_ATTRIBUTE } from '@/lib/core/config/env'
+import { isHosted } from '@/lib/core/config/env-flags'
+import { evaluateSubBlockCondition } from '@/lib/workflows/subblocks/visibility'
+import { getApiKeyCondition } from '@/blocks/utils'
+import { getHostedModels } from '@/providers/models'
+
+describe('hosted detection during client recovery', () => {
+  afterEach(() => {
+    document.documentElement.removeAttribute(PUBLIC_ENV_ATTRIBUTE)
+    Reflect.deleteProperty(window, '__ENV')
+  })
+
+  it('hides hosted model keys before the recovered layout installs runtime configuration', () => {
+    expect(window.__ENV).toBeUndefined()
+    expect(document.documentElement.getAttribute(PUBLIC_ENV_ATTRIBUTE)).toBeNull()
+    expect(isHosted).toBe(true)
+
+    for (const model of ['gpt-5.6-sol', 'claude-sonnet-5', 'gemini-2.5-pro']) {
+      expect(getHostedModels()).toContain(model)
+      expect(evaluateSubBlockCondition(getApiKeyCondition(), { model })).toBe(false)
+    }
+
+    document.documentElement.setAttribute(
+      PUBLIC_ENV_ATTRIBUTE,
+      JSON.stringify({ NEXT_PUBLIC_APP_URL: 'https://www.sim.ai' })
+    )
+
+    expect(getEnv('NEXT_PUBLIC_APP_URL')).toBe('https://www.sim.ai')
+    expect(isHosted).toBe(true)
+    expect(evaluateSubBlockCondition(getApiKeyCondition(), { model: 'gpt-5.6-sol' })).toBe(false)
+  })
+
+  it('still requires keys for models outside the hosted catalog', () => {
+    expect(evaluateSubBlockCondition(getApiKeyCondition(), { model: 'custom/model' })).toBe(true)
+  })
+})
diff --git a/apps/sim/lib/core/config/env-flags.test.ts b/apps/sim/lib/core/config/env-flags.test.ts
new file mode 100644
index 00000000000..fa30e64738e
--- /dev/null
+++ b/apps/sim/lib/core/config/env-flags.test.ts
@@ -0,0 +1,23 @@
+/**
+ * @vitest-environment node
+ */
+import { describe, expect, it, vi } from 'vitest'
+
+vi.hoisted(() => {
+  vi.stubEnv('NEXT_PUBLIC_APP_URL', 'https://self-hosted.example')
+  vi.stubEnv('NEXT_PUBLIC_FORCE_HOSTED', 'true')
+  vi.stubEnv('NODE_ENV', 'production')
+  vi.stubGlobal('window', { location: { hostname: 'www.sim.ai' } })
+})
+
+vi.unmock('@/lib/core/config/env')
+vi.unmock('@/lib/core/config/env-flags')
+
+import { isHosted, isProd } from '@/lib/core/config/env-flags'
+
+describe('configured hosted detection', () => {
+  it('preserves a configured self-hosted URL and ignores the development override in production', () => {
+    expect(isProd).toBe(true)
+    expect(isHosted).toBe(false)
+  })
+})
diff --git a/apps/sim/lib/core/config/env-flags.ts b/apps/sim/lib/core/config/env-flags.ts
index 1a954327eea..d90b2aa1e84 100644
--- a/apps/sim/lib/core/config/env-flags.ts
+++ b/apps/sim/lib/core/config/env-flags.ts
@@ -35,13 +35,16 @@ export const isTest = env.NODE_ENV === 'test'
 /**
  * Is this the hosted version of the application.
  * True for sim.ai and any subdomain of sim.ai (e.g. staging.sim.ai, dev.sim.ai).
+ * The browser hostname remains available when an error document boots without
+ * the root layout's runtime environment, before client rendering recovers it.
+ * A valid configured URL takes precedence; server detection stays env-only.
  */
 const appUrl = getEnv('NEXT_PUBLIC_APP_URL')
-let appHostname = ''
+let appHostname = typeof window === 'undefined' ? '' : window.location.hostname
 try {
-  appHostname = appUrl ? new URL(appUrl).hostname : ''
+  if (appUrl) appHostname = new URL(appUrl).hostname
 } catch {
-  // invalid URL — isHosted stays false
+  /** Keep the document hostname when the configured URL cannot be parsed. */
 }
 /**
  * Local-development escape hatch for exercising hosted-only paths (the sim-auto
diff --git a/apps/sim/lib/core/config/env.ts b/apps/sim/lib/core/config/env.ts
index 947688417a7..31f967a3b38 100644
--- a/apps/sim/lib/core/config/env.ts
+++ b/apps/sim/lib/core/config/env.ts
@@ -24,11 +24,11 @@ import { z } from 'zod'
  * hydration. So on a warm cache both module bodies and the first commit can run
  * before the parser has reached the assignment.
  *
- * An attribute has no such ordering problem. `<html>` is the first tag in the
- * document — ~490 bytes ahead of the first bootstrap script — so
- * `document.documentElement` already carries this value by the time *any*
- * script, framework or application, is able to execute. This is the race-free
- * transport; `window.__ENV` stays the public global and the preferred read.
+ * On a normally rendered document, the attribute is parsed before bootstrap
+ * scripts can execute. Next's server-rendering error document omits the root
+ * layout, so client recovery only installs the attribute when that layout
+ * mounts. Hosted detection also uses the browser hostname during this gap.
+ * `window.__ENV` stays the public global and the preferred read.
  */
 export const PUBLIC_ENV_ATTRIBUTE = 'data-public-env'