diff --git a/web/frontend/src/components/models/add-model-sheet.tsx b/web/frontend/src/components/models/add-model-sheet.tsx
index dbd41b534..1deaf9a06 100644
--- a/web/frontend/src/components/models/add-model-sheet.tsx
+++ b/web/frontend/src/components/models/add-model-sheet.tsx
@@ -6,7 +6,12 @@ import {
 import { useCallback, useEffect, useRef, useState } from "react"
 import { useTranslation } from "react-i18next"
 
-import { addModel, getCatalogs, setDefaultModel } from "@/api/models"
+import {
+  type ModelProviderOption,
+  addModel,
+  getCatalogs,
+  setDefaultModel,
+} from "@/api/models"
 import { ConfigChangeNotice } from "@/components/config-change-notice"
 import { maskedSecretPlaceholder } from "@/components/secret-placeholder"
 import {
@@ -111,6 +116,7 @@ interface AddModelSheetProps {
   onClose: () => void
   onSaved: () => void
   existingModelNames: string[]
+  providerOptions?: ModelProviderOption[]
 }
 
 export function AddModelSheet({
@@ -118,6 +124,7 @@ export function AddModelSheet({
   onClose,
   onSaved,
   existingModelNames,
+  providerOptions,
 }: AddModelSheetProps) {
   const { t } = useTranslation()
   const [form, setForm] = useState<AddForm>(EMPTY_ADD_FORM)
@@ -134,6 +141,7 @@ export function AddModelSheet({
   const [fetchedModels, setFetchedModels] = useState<string[]>([])
   const [catalogModels, setCatalogModels] = useState<string[]>([])
   const debounceRef = useRef<ReturnType<typeof setTimeout>>(undefined)
+  const scrollContainerRef = useRef<HTMLDivElement>(null)
   const apiKeyPlaceholder = maskedSecretPlaceholder(
     form.apiKey,
     t("models.field.apiKeyPlaceholder"),
@@ -283,6 +291,8 @@ export function AddModelSheet({
     try {
       if (form.extraBody.trim()) {
         extraBody = JSON.parse(form.extraBody.trim())
+      } else {
+        extraBody = {}
       }
     } catch {
       setServerError(
@@ -293,6 +303,8 @@ export function AddModelSheet({
     try {
       if (form.customHeaders.trim()) {
         customHeaders = JSON.parse(form.customHeaders.trim())
+      } else {
+        customHeaders = {}
       }
     } catch {
       setServerError(
@@ -362,7 +374,7 @@ export function AddModelSheet({
             </SheetDescription>
           </SheetHeader>
 
-          <div className="min-h-0 flex-1 overflow-y-auto">
+          <div className="min-h-0 flex-1 overflow-y-auto" ref={scrollContainerRef}>
             <div className="space-y-5 px-6 py-5">
               <Field
                 label={t("models.add.modelName")}
@@ -389,6 +401,9 @@ export function AddModelSheet({
                   value={form.provider}
                   onChange={handleProviderChange}
                   placeholder={t("models.field.providerPlaceholder")}
+                  backendOptions={providerOptions}
+                  filterCreateAllowed
+                  containerRef={scrollContainerRef}
                 />
               </Field>
 
diff --git a/web/frontend/src/components/models/edit-model-sheet.tsx b/web/frontend/src/components/models/edit-model-sheet.tsx
index d76bfc9fe..b05d61a65 100644
--- a/web/frontend/src/components/models/edit-model-sheet.tsx
+++ b/web/frontend/src/components/models/edit-model-sheet.tsx
@@ -8,6 +8,7 @@ import { useTranslation } from "react-i18next"
 
 import {
   type ModelInfo,
+  type ModelProviderOption,
   getCatalogs,
   setDefaultModel,
   updateModel,
@@ -65,6 +66,7 @@ interface EditModelSheetProps {
   open: boolean
   onClose: () => void
   onSaved: () => void
+  providerOptions?: ModelProviderOption[]
 }
 
 function normalizeApiBase(value: string): string {
@@ -126,6 +128,7 @@ export function EditModelSheet({
   open,
   onClose,
   onSaved,
+  providerOptions,
 }: EditModelSheetProps) {
   const { t } = useTranslation()
   const [form, setForm] = useState<EditForm>({
@@ -155,6 +158,7 @@ export function EditModelSheet({
   const [fetchedModels, setFetchedModels] = useState<string[]>([])
   const [catalogModels, setCatalogModels] = useState<string[]>([])
   const debounceRef = useRef<ReturnType<typeof setTimeout>>(undefined)
+  const scrollContainerRef = useRef<HTMLDivElement>(null)
   const initialForm = model ? buildInitialEditForm(model) : null
   const isDirty =
     model != null &&
@@ -256,6 +260,8 @@ export function EditModelSheet({
     try {
       if (form.extraBody.trim()) {
         extraBody = JSON.parse(form.extraBody.trim())
+      } else {
+        extraBody = {}
       }
     } catch {
       setError(
@@ -266,6 +272,8 @@ export function EditModelSheet({
     try {
       if (form.customHeaders.trim()) {
         customHeaders = JSON.parse(form.customHeaders.trim())
+      } else {
+        customHeaders = {}
       }
     } catch {
       setError(
@@ -343,7 +351,7 @@ export function EditModelSheet({
             </SheetDescription>
           </SheetHeader>
 
-          <div className="min-h-0 flex-1 overflow-y-auto">
+          <div className="min-h-0 flex-1 overflow-y-auto" ref={scrollContainerRef}>
             <div className="space-y-5 px-6 py-5">
               <Field
                 label={t("models.field.provider")}
@@ -353,6 +361,8 @@ export function EditModelSheet({
                   value={form.provider}
                   onChange={handleProviderChange}
                   placeholder={t("models.field.providerPlaceholder")}
+                  backendOptions={providerOptions}
+                  containerRef={scrollContainerRef}
                 />
               </Field>
 
diff --git a/web/frontend/src/components/models/models-page.tsx b/web/frontend/src/components/models/models-page.tsx
index f98377b2f..9c0c400db 100644
--- a/web/frontend/src/components/models/models-page.tsx
+++ b/web/frontend/src/components/models/models-page.tsx
@@ -8,7 +8,12 @@ import { useCallback, useEffect, useState } from "react"
 import { useTranslation } from "react-i18next"
 import { toast } from "sonner"
 
-import { type ModelInfo, getModels, setDefaultModel } from "@/api/models"
+import {
+  type ModelInfo,
+  type ModelProviderOption,
+  getModels,
+  setDefaultModel,
+} from "@/api/models"
 import { PageHeader } from "@/components/page-header"
 import { Button } from "@/components/ui/button"
 import { showSaveSuccessOrRestartToast } from "@/lib/restart-required"
@@ -33,6 +38,9 @@ interface ProviderGroup {
 export function ModelsPage() {
   const { t } = useTranslation()
   const [models, setModels] = useState<ModelInfo[]>([])
+  const [providerOptions, setProviderOptions] = useState<
+    ModelProviderOption[]
+  >([])
   const [loading, setLoading] = useState(true)
   const [fetchError, setFetchError] = useState("")
 
@@ -55,6 +63,7 @@ export function ModelsPage() {
         return a.model_name.localeCompare(b.model_name)
       })
       setModels(sorted)
+      setProviderOptions(data.provider_options || [])
       setFetchError("")
     } catch (e) {
       setFetchError(e instanceof Error ? e.message : t("models.loadError"))
@@ -200,6 +209,7 @@ export function ModelsPage() {
         open={editingModel !== null}
         onClose={() => setEditingModel(null)}
         onSaved={fetchModels}
+        providerOptions={providerOptions}
       />
 
       <AddModelSheet
@@ -207,6 +217,7 @@ export function ModelsPage() {
         onClose={() => setAddOpen(false)}
         onSaved={fetchModels}
         existingModelNames={models.map((model) => model.model_name)}
+        providerOptions={providerOptions}
       />
 
       <DeleteModelDialog
diff --git a/web/frontend/src/components/models/provider-combobox.tsx b/web/frontend/src/components/models/provider-combobox.tsx
index 104c279ae..3a6d3da30 100644
--- a/web/frontend/src/components/models/provider-combobox.tsx
+++ b/web/frontend/src/components/models/provider-combobox.tsx
@@ -20,27 +20,52 @@ import {
 import { cn } from "@/lib/utils"
 
 import { ProviderIcon } from "./provider-icon"
-import { KNOWN_PROVIDER_KEYS, PROVIDERS } from "./provider-registry"
+import {
+  type MergedProvider,
+  PROVIDERS,
+  mergeWithBackendOptions,
+} from "./provider-registry"
+import type { ModelProviderOption } from "@/api/models"
 
 interface ProviderComboboxProps {
   value: string
   onChange: (value: string) => void
   placeholder?: string
+  backendOptions?: ModelProviderOption[]
+  /** When true, only show providers with create_allowed from the backend. */
+  filterCreateAllowed?: boolean
+  /** Container element for the popover portal. Use to avoid scroll conflicts inside dialogs/sheets. */
+  containerRef?: React.RefObject<HTMLElement | null>
 }
 
 export function ProviderCombobox({
   value,
   onChange,
   placeholder,
+  backendOptions,
+  filterCreateAllowed,
+  containerRef,
 }: ProviderComboboxProps) {
   const { t } = useTranslation()
   const [open, setOpen] = useState(false)
   const [customMode, setCustomMode] = useState(false)
   const [customValue, setCustomValue] = useState("")
 
-  const sorted = [...PROVIDERS].sort((a, b) => b.priority - a.priority)
-  const selected = sorted.find((p) => p.key === value)
-  const isCustom = value && !KNOWN_PROVIDER_KEYS.has(value)
+  const allProviders: MergedProvider[] = backendOptions
+    ? mergeWithBackendOptions(backendOptions)
+    : [...PROVIDERS]
+        .sort((a, b) => b.priority - a.priority)
+        .map((p) => ({
+          ...p,
+          createAllowed: true,
+          defaultModelAllowed: false,
+        }))
+  const visible = filterCreateAllowed
+    ? allProviders.filter((p) => p.createAllowed)
+    : allProviders
+  const allKeys = new Set(allProviders.map((p) => p.key))
+  const selected = allProviders.find((p) => p.key === value)
+  const isCustom = value && !allKeys.has(value)
 
   const handleSelect = (currentValue: string) => {
     if (currentValue === "__custom__") {
@@ -97,7 +122,7 @@ export function ProviderCombobox({
           <IconChevronDown className="ml-2 size-4 shrink-0 opacity-50" />
         </Button>
       </PopoverTrigger>
-      <PopoverContent className="w-[--radix-popover-trigger-width] p-0">
+      <PopoverContent className="w-[--radix-popover-trigger-width] p-0" container={containerRef?.current}>
         {customMode ? (
           <div className="flex flex-col gap-2 p-2">
             <Input
@@ -142,7 +167,7 @@ export function ProviderCombobox({
             <CommandList>
               <CommandEmpty>{t("models.combobox.noProvider")}</CommandEmpty>
               <CommandGroup>
-                {sorted.map((provider) => (
+                {visible.map((provider) => (
                   <CommandItem
                     key={provider.key}
                     value={provider.key}
diff --git a/web/frontend/src/components/models/provider-registry.ts b/web/frontend/src/components/models/provider-registry.ts
index f24c094e4..cc18ccde6 100644
--- a/web/frontend/src/components/models/provider-registry.ts
+++ b/web/frontend/src/components/models/provider-registry.ts
@@ -4,6 +4,8 @@
  * should derive their data from this registry.
  */
 
+import type { ModelProviderOption } from "@/api/models"
+
 export interface ProviderDefinition {
   key: string
   label: string
@@ -464,3 +466,55 @@ function editDistance(a: string, b: string): number {
   }
   return dp[m][n]
 }
+
+// ── Backend options merge ────────────────────────────────────────────────────
+
+export interface MergedProvider extends ProviderDefinition {
+  createAllowed: boolean
+  defaultModelAllowed: boolean
+  defaultAuthMethod?: string
+  authMethodLocked?: boolean
+}
+
+/**
+ * Merge the frontend PROVIDERS registry with backend provider_options.
+ * Frontend provides presentation data (labels, icons, priority, etc.).
+ * Backend provides authoritative availability and policy fields.
+ */
+export function mergeWithBackendOptions(
+  backendOptions: ModelProviderOption[],
+): MergedProvider[] {
+  const backendMap = new Map(backendOptions.map((o) => [o.id, o]))
+  const merged: MergedProvider[] = []
+
+  // Start with frontend providers, enriched with backend policy
+  for (const p of PROVIDERS) {
+    const backend = backendMap.get(p.key)
+    merged.push({
+      ...p,
+      createAllowed: backend?.create_allowed ?? false,
+      defaultModelAllowed: backend?.default_model_allowed ?? false,
+      defaultAuthMethod: backend?.default_auth_method,
+      authMethodLocked: backend?.auth_method_locked,
+    })
+    if (backend) backendMap.delete(p.key)
+  }
+
+  // Add providers only known to the backend
+  for (const [key, backend] of backendMap) {
+    merged.push({
+      key,
+      label: key,
+      requiresApiKey: !backend.empty_api_key_allowed,
+      isLocal: backend.empty_api_key_allowed,
+      priority: 0,
+      createAllowed: backend.create_allowed,
+      defaultModelAllowed: backend.default_model_allowed,
+      defaultAuthMethod: backend.default_auth_method,
+      authMethodLocked: backend.auth_method_locked,
+      defaultApiBase: backend.default_api_base || undefined,
+    })
+  }
+
+  return merged.sort((a, b) => b.priority - a.priority)
+}
diff --git a/web/frontend/src/components/ui/popover.tsx b/web/frontend/src/components/ui/popover.tsx
index bba758093..c67bc5c91 100644
--- a/web/frontend/src/components/ui/popover.tsx
+++ b/web/frontend/src/components/ui/popover.tsx
@@ -9,9 +9,11 @@ const PopoverTrigger = PopoverPrimitive.Trigger
 
 const PopoverContent = React.forwardRef<
   React.ComponentRef<typeof PopoverPrimitive.Content>,
-  React.ComponentPropsWithoutRef<typeof PopoverPrimitive.Content>
->(({ className, align = "center", sideOffset = 4, ...props }, ref) => (
-  <PopoverPrimitive.Portal>
+  React.ComponentPropsWithoutRef<typeof PopoverPrimitive.Content> & {
+    container?: HTMLElement | null
+  }
+>(({ className, align = "center", sideOffset = 4, container, ...props }, ref) => (
+  <PopoverPrimitive.Portal container={container}>
     <PopoverPrimitive.Content
       ref={ref}
       align={align}