diff --git a/docs/specs/2026-09-20-web-settings-model-section-acceptance.md b/docs/specs/2026-09-20-web-settings-model-section-acceptance.md
index d03391652..50947ace5 100644
--- a/docs/specs/2026-09-20-web-settings-model-section-acceptance.md
+++ b/docs/specs/2026-09-20-web-settings-model-section-acceptance.md
@@ -154,7 +154,7 @@ seeded key is sent).
 | T <- A | Host | Steps | Observe (owning layer) | Red when | Rings | * |
 |---|---|---|---|---|---|---|
 | T3.1 <- A7 | yes | Click, in turn, deepseek, moonshot, minimax_global, ollama_chat. | Each head shows the mark and the name; a link only when `options.json` carries `homepage` or `key_url` for that slug; the status line reads connected / needs an API key / needs authorisation / needs an address, matching `authenticated` and `auth_type` in the reply. | a status line disagreeing with the reply; a link for a provider the reply gives none | T E V R | |
-| T3.2 <- A8 | yes | Moonshot: paste a key, press the eye, press it again, connect. Reopen the row; press the eye over the empty field, press "update", press the eye again. | `eval` on the key input's `type` reads `text` then `password`; after connect `jq .providers.moonshot.apiKey` equals the pasted string and the status reads connected; on reopen the field is empty with the "update" placeholder; the eye over it fills it with the stored key as `text`, carried by the one `model.reveal_key` answer to that press; "update" sends `model.save_key` without `api_key`; the second press empties the field and masks it; no other frame in `web.log` after the connect carries the stored key (T3.3 checks the address save). Amended 2026-10-09 (design C10): the stored key used to appear in no field at all. | the stored key appears in any frame other than that `model.reveal_key` answer, or in the field without the eye pressed; an unedited revealed key is sent back; the eye does not flip the type | T P E V R | |
+| T3.2 <- A8 | yes | Moonshot: paste a key, press the eye, press it again, connect. Reopen the row; press the eye over the empty field, press "update", press the eye again. | `eval` on the key input's `type` reads `text` then `password`; after connect `jq .providers.moonshot.apiKey` equals the pasted string and the status reads connected; on reopen the field is empty with the "update" placeholder; the eye over it fills it with the stored key as `text`, carried by the one `model.reveal_key` answer to that press; "update" sends no frame and the pane says there is no new key to save; the second press empties the field and masks it; no other frame in `web.log` after the connect carries the stored key (T3.3 checks the address save). Amended 2026-10-09 (design C10): the stored key used to appear in no field at all. | the stored key appears in any frame other than that `model.reveal_key` answer, or in the field without the eye pressed; an unedited revealed key is sent back, or "update" over it sends any frame; the eye does not flip the type | T P E V R | |
 | T3.3 <- A9 | yes | From T3.2 (Moonshot connected). OpenRouter: the address field is in the body. Moonshot: open Advanced, set the address to `https://api.moonshot.cn/v1`, save; press reset. | `eval`: openrouter's address input is not inside the Advanced fold; moonshot's is. The save's frame is `model.set_fields` with no `api_key` -- the stored key never returns to the wire; after save `jq .providers.moonshot.apiBase` equals the address and `apiKey` is unchanged (`diff` shows one path); after reset `apiBase` is gone or equals the registry default and the button disappears. | the field in the wrong place; the key changed; reset writing something else | T P E V R | |
 | T3.4 <- A10 | yes | Azure OpenAI: key, address, deployment `gpt-4o-eu`, API version `2024-10-21`, connect. | `jq .providers.azure_openai` holds all four (prior T3.4's check); the two Azure fields sit under the address in the body. | any field missing | T E V R | |
 | T3.5 <- A11 | yes | MiniMax Global: read the pane; press "authorise in browser"; wait for the code. | Snapshot: the prototype's layout -- head, an authorisation section, no key field, no CLI instruction; after the press one `model.oauth_login` frame, and the device code and URL drawn in the pane (the flow starts without an account; only completing it needs one). | the CLI text appears; no code within the reply's `expires_in` | T P V R | |
diff --git a/i18n/messages.json b/i18n/messages.json
index 25850406d..dc098c89d 100644
--- a/i18n/messages.json
+++ b/i18n/messages.json
@@ -7559,6 +7559,10 @@
       "en": "Enter the API key first",
       "zh": "先填入 API Key"
     },
+    "gui.settings.providers.key_unchanged": {
+      "en": "No new API key to save. To replace the saved one, type a new key in the API key field, then press {button}.",
+      "zh": "没有新的 API Key 要保存。要更换，先在「API 密钥」框里填入新的，再点「{button}」。"
+    },
     "gui.settings.providers.key_not_ascii": {
       "en": "This doesn't look like an API key: it has characters a key never contains. Check what was pasted",
       "zh": "这不像是 API Key：里面有 Key 不会包含的字符，请检查粘贴的内容"
diff --git a/ui-tui/src/i18n/messages.generated.ts b/ui-tui/src/i18n/messages.generated.ts
index cb9324c23..d4e85b9f4 100644
--- a/ui-tui/src/i18n/messages.generated.ts
+++ b/ui-tui/src/i18n/messages.generated.ts
@@ -2136,6 +2136,8 @@ export const UI_TEXT: Record<Locale, Record<string, string>> = {
     'gui.settings.providers.paste_key': 'Paste an API key',
     'gui.settings.providers.pick_one': 'Choose a provider on the left',
     'gui.settings.providers.key_first': 'Enter the API key first',
+    'gui.settings.providers.key_unchanged':
+      'No new API key to save. To replace the saved one, type a new key in the API key field, then press {button}.',
     'gui.settings.providers.key_not_ascii':
       "This doesn't look like an API key: it has characters a key never contains. Check what was pasted",
     'gui.settings.providers.base': 'Service address',
@@ -4714,6 +4716,8 @@ export const UI_TEXT: Record<Locale, Record<string, string>> = {
     'gui.settings.providers.paste_key': '粘贴 API Key',
     'gui.settings.providers.pick_one': '在左边选一家服务商',
     'gui.settings.providers.key_first': '先填入 API Key',
+    'gui.settings.providers.key_unchanged':
+      '没有新的 API Key 要保存。要更换，先在「API 密钥」框里填入新的，再点「{button}」。',
     'gui.settings.providers.key_not_ascii': '这不像是 API Key：里面有 Key 不会包含的字符，请检查粘贴的内容',
     'gui.settings.providers.base': '服务地址',
     'gui.settings.providers.api_base': 'API 地址',
diff --git a/ui-web/src/features/settings/providers/ProviderDetail.test.tsx b/ui-web/src/features/settings/providers/ProviderDetail.test.tsx
index 57d3ad77b..60c8fd900 100644
--- a/ui-web/src/features/settings/providers/ProviderDetail.test.tsx
+++ b/ui-web/src/features/settings/providers/ProviderDetail.test.tsx
@@ -42,6 +42,9 @@ async function open(slug: string): Promise<void> {
   await act(async () => { store.set({ provider: slug }) })
 }
 
+/* What Update over a connected provider's key field says when it holds no new key. */
+const UNCHANGED = 'gui.settings.providers.key_unchanged {"button":"gui.settings.update"}'
+
 /* The connection card's key field and the eye beside it. */
 const keyField = (): HTMLInputElement =>
   document.querySelector('.settings-tp-main input[aria-label="gui.settings.providers.api_key"]') as HTMLInputElement
@@ -124,17 +127,29 @@ describe('the eye beside a connected provider\'s key', () => {
       fireEvent.click(keyField().closest('.settings-taglist')!.querySelector(':scope > button.mini')!)
     }],
     ['Enter', (): void => { fireEvent.keyDown(keyField(), { key: 'Enter' }) }],
-  ])('sends no key on %s while the revealed one is unedited: the stored key does not go back', async (_how, press) => {
-    /* What the empty field sends, so it is refused the way the empty field is,
-       rather than rewriting the config with the key it already holds. */
+  ])('sends nothing on %s while the revealed key is unedited, and says there is no new key', async (_how, press) => {
+    /* The stored key does not go back, and nothing else would: the server
+       could only refuse an empty save, in English. */
     const { calls } = install(snap(), { revealKey: answering('sk-or-saved') })
     await open('openrouter')
     await act(async () => { fireEvent.click(keyEye()) })
     await waitFor(() => expect(keyField().value).toBe('sk-or-saved'))
 
     await act(async () => { press() })
-    expect(calls.filter(([name]) => name === 'provider').map(([, args]) => args))
-      .toEqual([{ op: 'save_key', slug: 'openrouter' }])
+    expect(calls.filter(([name]) => name === 'provider')).toEqual([])
+    expect(screen.getByRole('alert').textContent).toBe(UNCHANGED)
+    expect(keyField().value).toBe('sk-or-saved')
+  })
+
+  it('sends nothing on Update over the empty field of a connected provider, and says why', async () => {
+    const { calls } = install(snap())
+    await open('openrouter')
+    expect(keyField().value).toBe('')
+    await act(async () => {
+      fireEvent.click(keyField().closest('.settings-taglist')!.querySelector(':scope > button.mini')!)
+    })
+    expect(calls.filter(([name]) => name === 'provider')).toEqual([])
+    expect(screen.getByRole('alert').textContent).toBe(UNCHANGED)
   })
 
   it('saves an edited revealed key as the new key', async () => {
@@ -644,6 +659,73 @@ describe('provider detail, the address of a direct vendor', () => {
   })
 })
 
+describe('an endpoint provider (custom, Azure) saved without a new key', () => {
+  /* `model.save_key` refuses custom, Azure and MiniMax CN without a key, so a
+     press with nothing new says so instead of sending a save that can only come
+     back in English -- and an address edited on its own goes the way any other
+     field does, through `model.set_fields`, with no key asked for again. */
+  const withCustom = (on: boolean): ReturnType<typeof snap> => {
+    const data = snap()
+    data.providers = [...data.providers, { id: 'custom', name: 'Custom', models: [], configured: [], on, kind: 'endpoint', acceptsKey: true, needsBase: true }]
+    ;(data.raw.providers as Record<string, unknown>).custom = { apiBase: 'https://relay.example/v1' }
+    return data
+  }
+  const baseField = (): HTMLInputElement => screen.getByLabelText('gui.settings.providers.base') as HTMLInputElement
+  const keyUpdate = (): HTMLButtonElement =>
+    keyField().closest('.settings-taglist')!.querySelector(':scope > button.mini') as HTMLButtonElement
+  const saves = (calls: Call[]): unknown[] => calls.filter(([name]) => name === 'provider').map(([, args]) => args)
+
+  it('says there is no new key when nothing was changed', async () => {
+    const { calls } = install(withCustom(true))
+    await open('custom')
+    await act(async () => { fireEvent.click(keyUpdate()) })
+    expect(saves(calls)).toEqual([])
+    expect(screen.getByRole('alert').textContent).toBe(UNCHANGED)
+  })
+
+  it('saves an edited address on its own, without asking for the key again', async () => {
+    const { calls } = install(withCustom(true))
+    await open('custom')
+    fireEvent.change(baseField(), { target: { value: 'https://relay2.example/v1' } })
+    await act(async () => { fireEvent.click(keyUpdate()) })
+    expect(saves(calls)).toEqual([])
+    expect(calls.filter(([name]) => name === 'setFields'))
+      .toEqual([['setFields', { slug: 'custom', fields: { api_base: 'https://relay2.example/v1' } }]])
+    expect(screen.queryByRole('alert')).toBeNull()
+  })
+
+  it('saves an edited address on its own with the revealed key still unedited in the field', async () => {
+    /* The stored key on screen as text is still no new key (C10): it does not
+       go back, and the address goes without it. */
+    const { calls } = install(withCustom(true), { revealKey: async () => 'cu-saved' })
+    await open('custom')
+    await act(async () => { fireEvent.click(keyEye()) })
+    await waitFor(() => expect(keyField().value).toBe('cu-saved'))
+    fireEvent.change(baseField(), { target: { value: 'https://relay2.example/v1' } })
+    await act(async () => { fireEvent.click(keyUpdate()) })
+    expect(saves(calls)).toEqual([])
+    expect(calls.filter(([name]) => name === 'setFields'))
+      .toEqual([['setFields', { slug: 'custom', fields: { api_base: 'https://relay2.example/v1' } }]])
+  })
+
+  it('saves an edited address with a key typed beside it', async () => {
+    const { calls } = install(withCustom(true))
+    await open('custom')
+    fireEvent.change(baseField(), { target: { value: 'https://relay2.example/v1' } })
+    fireEvent.change(keyField(), { target: { value: 'sk-relay' } })
+    await act(async () => { fireEvent.click(keyUpdate()) })
+    expect(saves(calls)).toEqual([{ op: 'save_key', slug: 'custom', api_key: 'sk-relay', api_base: 'https://relay2.example/v1' }])
+  })
+
+  it('asks for the key first on a provider not yet connected', async () => {
+    const { calls } = install(withCustom(false))
+    await open('custom')
+    await act(async () => { fireEvent.click(screen.getByText('gui.settings.providers.connect')) })
+    expect(saves(calls)).toEqual([])
+    expect(screen.getByRole('alert').textContent).toBe('gui.settings.providers.key_first')
+  })
+})
+
 describe('provider detail, Azure', () => {
   it('shows the stored deployment and API version from the config section', async () => {
     const data = snap()
diff --git a/ui-web/src/features/settings/providers/ProviderDetail.tsx b/ui-web/src/features/settings/providers/ProviderDetail.tsx
index 585350547..59209653f 100644
--- a/ui-web/src/features/settings/providers/ProviderDetail.tsx
+++ b/ui-web/src/features/settings/providers/ProviderDetail.tsx
@@ -99,7 +99,8 @@ function Connection({ p }: { p: ProviderRow }): JSX.Element {
     setKey(saved)
     setRevealed(saved)
   }
-  const [base, setBase] = useState(p.apiBase || rawStr(store.get().snap.raw, p.id, 'apiBase') || p.defaultApiBase || '')
+  const shownBase = p.apiBase || rawStr(store.get().snap.raw, p.id, 'apiBase') || p.defaultApiBase || ''
+  const [base, setBase] = useState(shownBase)
   const kind = kindOf(p)
   const checking = store.isBusy(busy(p.id))
   /* Where this block draws the address field, if anywhere: above the key for a
@@ -117,8 +118,26 @@ function Connection({ p }: { p: ProviderRow }): JSX.Element {
        here) for no change, so it goes as an empty field does. */
     const k = key === revealed ? '' : key.trim()
     const b = base.trim()
-    if (needsKey(p) && !k && !p.on) { store.refuse(t('gui.settings.providers.key_first')); return }
+    /* A key-shaped provider, or an endpoint (custom, Azure), connects by its
+       key: `model.save_key` refuses such a save without one -- all but
+       Bedrock's, which takes an ambient credential, accepts it and changes
+       nothing. */
+    const endpointKey = p.kind === 'endpoint' && takesKey(p)
+    if ((needsKey(p) || endpointKey) && !k && !p.on) { store.refuse(t('gui.settings.providers.key_first')); return }
     if (takesBase(p) && !b) { store.refuse(t('gui.settings.providers.base_first')); return }
+    if (!k && (endpointKey || (needsKey(p) && !(b && basePlace)))) {
+      /* An endpoint's edited address with no new key goes on its own, the way
+         any other field does (`model.set_fields`, as AddressRow sends it):
+         `model.save_key` would demand the key again. */
+      if (endpointKey && b !== shownBase.trim()) {
+        void store.run(busy(p.id), () => store.source().setFields(p.id, { api_base: b }))
+        return
+      }
+      /* Nothing new to send: the save could only be refused, in English, or
+         change nothing, so the page says what pressing it would have needed. */
+      store.refuse(t('gui.settings.providers.key_unchanged', { button: t('gui.settings.update') }))
+      return
+    }
     const params: Record<string, unknown> = { slug: p.id }
     if (k) params.api_key = k
     if (b && basePlace) params.api_base = b