diff --git a/apps/web/src/components/settings/ProviderInstanceCard.tsx b/apps/web/src/components/settings/ProviderInstanceCard.tsx
index 05a7471d44e34..3c92248b62c24 100644
--- a/apps/web/src/components/settings/ProviderInstanceCard.tsx
+++ b/apps/web/src/components/settings/ProviderInstanceCard.tsx
@@ -676,7 +676,7 @@ interface ProviderInstanceCardProps {
   readonly onSelect?: (() => void) | undefined;
   readonly readOnly?: boolean | undefined;
   readonly canWriteSettings?: boolean;
-  readonly onUpdate: (nextInstance: ProviderInstanceConfig) => void;
+  readonly onUpdate: (nextInstance: ProviderInstanceConfig) => Promise<boolean>;
   readonly onDelete?: (() => void) | undefined;
   readonly headerAction?: ReactNode | undefined;
   readonly setup?: ReactNode;
@@ -877,7 +877,7 @@ export function ProviderInstanceCard({
       next.map(toCustomModelSetting),
     );
     const { config: _omit, ...rest } = instance;
-    onUpdate({ ...rest, config: nextConfig } as ProviderInstanceConfig);
+    return onUpdate({ ...rest, config: nextConfig } as ProviderInstanceConfig);
   });
 
   const updateEnvironment = (environment: ReadonlyArray<ProviderInstanceEnvironmentVariable>) => {
diff --git a/apps/web/src/components/settings/ProviderModelsSection.browser.test.tsx b/apps/web/src/components/settings/ProviderModelsSection.browser.test.tsx
index bf193053e94a6..a0661fd3e8742 100644
--- a/apps/web/src/components/settings/ProviderModelsSection.browser.test.tsx
+++ b/apps/web/src/components/settings/ProviderModelsSection.browser.test.tsx
@@ -1,12 +1,13 @@
 import { ProviderDriverKind, ProviderInstanceId } from "@t3tools/contracts";
+import type { ComponentProps } from "react";
 import { expect, it, vi } from "vite-plus/test";
+import { userEvent } from "vite-plus/test/browser";
 
-import { render } from "../../../test/render";
+import { act, render } from "../../../test/render";
 import { ProviderModelsSection } from "./ProviderModelsSection";
 
-it("lists a favorite the provider no longer reports so it can be unstarred", async () => {
-  const onToggleFavorite = vi.fn();
-  await using screen = await render(
+function section(props: Partial<ComponentProps<typeof ProviderModelsSection>>) {
+  return (
     <ProviderModelsSection
       instanceId={ProviderInstanceId.make("claude")}
       driverKind={ProviderDriverKind.make("claude")}
@@ -14,15 +15,53 @@ it("lists a favorite the provider no longer reports so it can be unstarred", asy
       customModels={[]}
       canManageCustomModels
       hiddenModels={[]}
-      favoriteModels={["retired-model"]}
+      favoriteModels={[]}
       modelOrder={[]}
-      onChange={() => {}}
+      onChange={async () => true}
       onHiddenModelsChange={() => {}}
       onFavoriteModelsChange={() => {}}
-      onToggleFavorite={onToggleFavorite}
+      onToggleFavorite={() => {}}
       onModelOrderChange={() => {}}
-    />,
+      {...props}
+    />
+  );
+}
+
+it("lists a favorite the provider no longer reports so it can be unstarred", async () => {
+  const onToggleFavorite = vi.fn();
+  await using screen = await render(
+    section({ favoriteModels: ["retired-model"], onToggleFavorite }),
   );
   await screen.getByRole("button", { name: "Remove retired-model from favorites" }).click();
   expect(onToggleFavorite).toHaveBeenCalledWith("retired-model");
 });
+
+it("keeps a custom model draft until it saves, so a failed save can be retried", async () => {
+  const saves: Array<(saved: boolean) => void> = [];
+  const onChange = () => new Promise<boolean>((resolve) => saves.push(resolve));
+  await using screen = await render(section({ onChange }));
+  const addCustomModel = screen.getByRole("button", { name: "Add custom model" });
+  const input = screen.getByRole("textbox");
+  const add = screen.getByRole("button", { name: "Add", exact: true });
+
+  await userEvent.click(addCustomModel);
+  await userEvent.type(input, "my-model{Enter}");
+  await expect.element(add).toBeDisabled();
+  await userEvent.keyboard("{Enter}");
+  expect(saves).toHaveLength(1);
+  await act(() => saves[0]!(false));
+  await expect.element(add).toBeEnabled();
+  await expect.element(input).toHaveValue("my-model");
+
+  await userEvent.click(add);
+  await act(() => saves[1]!(true));
+  await expect.element(input).not.toBeInTheDocument();
+
+  // A save the user cancelled must not close the draft opened after it.
+  await userEvent.click(addCustomModel);
+  await userEvent.type(input, "other-model{Enter}");
+  await userEvent.click(screen.getByRole("button", { name: "Cancel" }));
+  await userEvent.click(addCustomModel);
+  await act(() => saves[2]!(true));
+  await expect.element(add).toBeEnabled();
+});
diff --git a/apps/web/src/components/settings/ProviderModelsSection.tsx b/apps/web/src/components/settings/ProviderModelsSection.tsx
index 39583592b7360..175701dfe49a1 100644
--- a/apps/web/src/components/settings/ProviderModelsSection.tsx
+++ b/apps/web/src/components/settings/ProviderModelsSection.tsx
@@ -109,7 +109,8 @@ interface ProviderModelsSectionProps {
   readonly hiddenModels: ReadonlyArray<string>;
   readonly favoriteModels: ReadonlyArray<string>;
   readonly modelOrder: ReadonlyArray<string>;
-  readonly onChange: (next: ReadonlyArray<CustomModelDefinition>) => void;
+  /** Resolves true once the custom models are saved. */
+  readonly onChange: (next: ReadonlyArray<CustomModelDefinition>) => Promise<boolean>;
   readonly onHiddenModelsChange: (
     next: ReadonlyArray<string>,
     affectedModels: ReadonlyArray<string>,
@@ -137,6 +138,8 @@ export function ProviderModelsSection({
 }: ProviderModelsSectionProps) {
   const [input, setInput] = useState("");
   const [isAdding, setIsAdding] = useState(false);
+  const [isSaving, setIsSaving] = useState(false);
+  const addAttemptRef = useRef(0);
   const [filter, setFilter] = useState("");
   const [error, setError] = useState<string | null>(null);
   const [editingSlug, setEditingSlug] = useState<string | null>(null);
@@ -189,8 +192,8 @@ export function ProviderModelsSection({
   const allBuiltInModelsHidden =
     builtInModels.length > 0 && builtInModels.every((model) => hiddenModels.includes(model.slug));
 
-  const handleAdd = () => {
-    if (!canManageCustomModels || driverKind === "antigravity") return;
+  const handleAdd = async () => {
+    if (!canManageCustomModels || driverKind === "antigravity" || isSaving) return;
     const normalized = normalizeCustomModelSlug(input);
     if (!normalized) {
       setError("Enter a model slug.");
@@ -209,15 +212,25 @@ export function ProviderModelsSection({
       return;
     }
 
+    addAttemptRef.current += 1;
+    const attempt = addAttemptRef.current;
+    setIsSaving(true);
+    const saved = await onChange([
+      ...customModels,
+      { slug: normalized, name: normalized, capabilities: null },
+    ]);
+    setIsSaving(false);
+    // Cancel bumps the attempt, so a late save cannot close the draft opened after it.
+    if (!saved || attempt !== addAttemptRef.current) return;
     scrollToSlugRef.current = normalized;
     setFilter("");
-    onChange([...customModels, { slug: normalized, name: normalized, capabilities: null }]);
     setInput("");
     setError(null);
     setIsAdding(false);
   };
 
   const cancelAdd = () => {
+    addAttemptRef.current += 1;
     setInput("");
     setError(null);
     setIsAdding(false);
@@ -226,7 +239,7 @@ export function ProviderModelsSection({
   const handleRemove = (slug: string) => {
     if (!canManageCustomModels) return;
     if (editingSlug === slug) setEditingSlug(null);
-    onChange(customModels.filter((entry) => entry.slug !== slug));
+    void onChange(customModels.filter((entry) => entry.slug !== slug));
     onModelOrderChange(modelOrder.filter((model) => model !== slug));
     onFavoriteModelsChange(favoriteModels.filter((model) => model !== slug));
     setError(null);
@@ -234,7 +247,7 @@ export function ProviderModelsSection({
 
   const handleSaveEdit = (next: CustomModelDefinition) => {
     if (!canManageCustomModels) return;
-    onChange(customModels.map((entry) => (entry.slug === next.slug ? next : entry)));
+    void onChange(customModels.map((entry) => (entry.slug === next.slug ? next : entry)));
     setEditingSlug(null);
   };
 
@@ -411,6 +424,7 @@ export function ProviderModelsSection({
             id={`provider-instance-${instanceId}-custom-model`}
             size="sm"
             autoFocus
+            readOnly={isSaving}
             value={input}
             onChange={(event) => {
               setInput(event.target.value);
@@ -424,13 +438,13 @@ export function ProviderModelsSection({
               }
               if (event.key !== "Enter") return;
               event.preventDefault();
-              handleAdd();
+              void handleAdd();
             }}
             placeholder={driverKind ? CUSTOM_MODEL_PLACEHOLDER_BY_KIND[driverKind] : "model-slug"}
             spellCheck={false}
           />
           <div className="flex shrink-0 gap-2">
-            <Button size="sm" variant="outline" onClick={handleAdd}>
+            <Button size="sm" variant="outline" disabled={isSaving} onClick={handleAdd}>
               Add
             </Button>
             <Button size="sm" variant="ghost" onClick={cancelAdd}>
diff --git a/apps/web/src/components/settings/ProviderSettingsPanel.tsx b/apps/web/src/components/settings/ProviderSettingsPanel.tsx
index aca6e5eb56fc5..c3cf285980147 100644
--- a/apps/web/src/components/settings/ProviderSettingsPanel.tsx
+++ b/apps/web/src/components/settings/ProviderSettingsPanel.tsx
@@ -808,6 +808,7 @@ export function EnvironmentProviderSettings({
         description: error instanceof Error ? error.message : "The settings update failed.",
       });
     }
+    return result._tag !== "Failure";
   };
 
   const updateInstance = useStableCallback(
@@ -821,7 +822,7 @@ export function EnvironmentProviderSettings({
         isDisabling &&
         resolveAppModelSelectionState(settings, serverProviders).instanceId === instanceId &&
         readEnvironmentScope(environmentId, AuthSettingsWriteScope);
-      void persistInstance(
+      return persistInstance(
         instanceId,
         next,
         shouldClearTextGen ? DEFAULT_UNIFIED_SETTINGS.textGenerationModelSelection : undefined,
@@ -1197,11 +1198,11 @@ interface ProviderInstanceRowActions {
     instanceId: ProviderInstanceId,
     previous: ProviderInstanceConfig,
     next: ProviderInstanceConfig,
-  ) => void;
+  ) => Promise<boolean>;
   readonly enableInstance: (
     instanceId: ProviderInstanceId,
     next: ProviderInstanceConfig,
-  ) => Promise<void>;
+  ) => Promise<boolean>;
   readonly deleteInstance: (
     instanceId: ProviderInstanceId,
     instance: ProviderInstanceConfig,