diff --git a/apps/desktop/src/app/settings/custom-endpoints-settings.test.tsx b/apps/desktop/src/app/settings/custom-endpoints-settings.test.tsx
index 8aa6f4b577..d144ea3dee 100644
--- a/apps/desktop/src/app/settings/custom-endpoints-settings.test.tsx
+++ b/apps/desktop/src/app/settings/custom-endpoints-settings.test.tsx
@@ -6,6 +6,7 @@ import type { CustomEndpointsResponse } from '@/types/hermes'
 
 const getCustomEndpoints = vi.fn()
 const saveCustomEndpoint = vi.fn()
+const validateCustomEndpoint = vi.fn()
 const notify = vi.fn()
 const notifyError = vi.fn()
 const triggerHaptic = vi.fn()
@@ -16,7 +17,7 @@ vi.mock('@/hermes', async importOriginal => ({
   deleteCustomEndpoint: vi.fn(),
   getCustomEndpoints: (...args: unknown[]) => getCustomEndpoints(...args),
   saveCustomEndpoint: (...args: unknown[]) => saveCustomEndpoint(...args),
-  validateCustomEndpoint: vi.fn()
+  validateCustomEndpoint: (...args: unknown[]) => validateCustomEndpoint(...args)
 }))
 vi.mock('./profile-scope', () => ({ ActiveProfileNote: () => null }))
 vi.mock('@/lib/haptics', () => ({ triggerHaptic: (...args: unknown[]) => triggerHaptic(...args) }))
@@ -54,6 +55,61 @@ afterEach(() => {
 })
 
 describe('CustomEndpointsSettings', () => {
+  it('sends the chosen API mode and discovered alias metadata on Save (#93622)', async () => {
+    getCustomEndpoints.mockResolvedValue(emptyResponse)
+    validateCustomEndpoint.mockResolvedValue({
+      message: '',
+      model_details: [
+        { id: 'gpt-5.6-sol' },
+        { canonical_model: 'gpt-5.6-sol', id: 'gpt-5.6-sol-high', reasoning_effort: 'high' }
+      ],
+      models: ['gpt-5.6-sol', 'gpt-5.6-sol-high'],
+      ok: true,
+      reachable: true
+    })
+    saveCustomEndpoint.mockResolvedValue(savedResponse)
+    const { CustomEndpointsSettings } = await import('./custom-endpoints-settings')
+
+    render(<CustomEndpointsSettings />)
+
+    await screen.findByText('No custom endpoints')
+    fireEvent.change(screen.getByPlaceholderText('Axet Proxy'), { target: { value: 'Responses gateway' } })
+    fireEvent.change(screen.getByPlaceholderText('http://127.0.0.1:8081/v1'), {
+      target: { value: 'https://responses-gateway.example.com/v1' }
+    })
+    fireEvent.click(screen.getByRole('button', { name: 'Responses API' }))
+    await act(async () => {
+      fireEvent.click(screen.getByRole('button', { name: 'Test' }))
+    })
+    fireEvent.change(screen.getByPlaceholderText('gpt-5.4'), { target: { value: 'gpt-5.6-sol-high' } })
+    fireEvent.click(screen.getByRole('button', { name: 'Save' }))
+
+    expect(validateCustomEndpoint).toHaveBeenCalledWith(expect.objectContaining({ api_mode: 'codex_responses' }))
+    expect(saveCustomEndpoint).toHaveBeenCalledWith(
+      expect.objectContaining({
+        api_mode: 'codex_responses',
+        model: 'gpt-5.6-sol-high',
+        model_details: expect.arrayContaining([
+          expect.objectContaining({ canonical_model: 'gpt-5.6-sol', id: 'gpt-5.6-sol-high', reasoning_effort: 'high' })
+        ]),
+        models: ['gpt-5.6-sol', 'gpt-5.6-sol-high']
+      })
+    )
+  })
+
+  it('hydrates the API mode from a saved endpoint', async () => {
+    getCustomEndpoints.mockResolvedValue({
+      ...savedResponse,
+      endpoints: [{ ...savedResponse.endpoints[0], api_mode: 'anthropic_messages' }]
+    })
+    const { CustomEndpointsSettings } = await import('./custom-endpoints-settings')
+
+    render(<CustomEndpointsSettings />)
+
+    await screen.findByText('Profile A')
+    expect(screen.getByRole('button', { name: 'Anthropic Messages' }).getAttribute('aria-pressed')).toBe('true')
+  })
+
   it('drops a pending save completion after its profile-scoped view unmounts', async () => {
     let resolveSave!: (value: CustomEndpointsResponse) => void
     saveCustomEndpoint.mockReturnValue(new Promise(resolve => (resolveSave = resolve)))
diff --git a/apps/desktop/src/app/settings/custom-endpoints-settings.tsx b/apps/desktop/src/app/settings/custom-endpoints-settings.tsx
index 6259c73f42..2fb04a9ade 100644
--- a/apps/desktop/src/app/settings/custom-endpoints-settings.tsx
+++ b/apps/desktop/src/app/settings/custom-endpoints-settings.tsx
@@ -3,6 +3,7 @@ import { useEffect, useRef, useState } from 'react'
 import { Button } from '@/components/ui/button'
 import { Checkbox } from '@/components/ui/checkbox'
 import { Input } from '@/components/ui/input'
+import { SegmentedControl } from '@/components/ui/segmented-control'
 import {
   activateCustomEndpoint,
   deleteCustomEndpoint,
@@ -16,7 +17,12 @@ import { Check, Globe, Loader2, Plus, Save, Trash2, Zap } from '@/lib/icons'
 import { cn } from '@/lib/utils'
 import { confirm } from '@/store/confirm'
 import { notify, notifyError } from '@/store/notifications'
-import type { CustomEndpoint, CustomEndpointUpdate } from '@/types/hermes'
+import type {
+  CustomEndpoint,
+  CustomEndpointApiMode,
+  CustomEndpointModelDetail,
+  CustomEndpointUpdate
+} from '@/types/hermes'
 
 import { EmptyState, Pill, SectionHeading, SettingsContent, SettingsSkeleton } from './primitives'
 import { ActiveProfileNote } from './profile-scope'
@@ -28,6 +34,7 @@ interface CustomEndpointsSettingsProps {
 
 interface EndpointForm {
   apiKey: string
+  apiMode: CustomEndpointApiMode
   baseUrl: string
   contextLength: string
   discoverModels: boolean
@@ -37,8 +44,18 @@ interface EndpointForm {
   name: string
 }
 
+// Same choices as `hermes model`'s custom-provider setup; '' = runtime auto-detect.
+// This panel is not internationalized — keep the literals it has.
+const API_MODE_OPTIONS: readonly { id: CustomEndpointApiMode; label: string }[] = [
+  { id: '', label: 'Auto-detect' },
+  { id: 'chat_completions', label: 'Chat Completions' },
+  { id: 'codex_responses', label: 'Responses API' },
+  { id: 'anthropic_messages', label: 'Anthropic Messages' }
+]
+
 const EMPTY_FORM: EndpointForm = {
   apiKey: '',
+  apiMode: '',
   baseUrl: '',
   contextLength: '',
   discoverModels: true,
@@ -51,6 +68,7 @@ const EMPTY_FORM: EndpointForm = {
 function formFromEndpoint(endpoint: CustomEndpoint): EndpointForm {
   return {
     apiKey: '',
+    apiMode: endpoint.api_mode ?? '',
     baseUrl: endpoint.base_url,
     contextLength: endpoint.context_length ? String(endpoint.context_length) : '',
     discoverModels: endpoint.discover_models,
@@ -61,7 +79,11 @@ function formFromEndpoint(endpoint: CustomEndpoint): EndpointForm {
   }
 }
 
-function toPayload(form: EndpointForm, models?: string[]): CustomEndpointUpdate {
+function toPayload(
+  form: EndpointForm,
+  models?: string[],
+  modelDetails?: CustomEndpointModelDetail[]
+): CustomEndpointUpdate {
   const contextLength = Number.parseInt(form.contextLength, 10)
 
   return {
@@ -70,10 +92,12 @@ function toPayload(form: EndpointForm, models?: string[]): CustomEndpointUpdate
     base_url: form.baseUrl.trim(),
     model: form.model.trim(),
     api_key: form.apiKey.trim() || undefined,
+    api_mode: form.apiMode,
     context_length: Number.isFinite(contextLength) && contextLength > 0 ? contextLength : undefined,
     discover_models: form.discoverModels,
     make_default: form.makeDefault,
-    models: models?.length ? models : undefined
+    models: models?.length ? models : undefined,
+    model_details: modelDetails?.length ? modelDetails : undefined
   }
 }
 
@@ -88,6 +112,9 @@ export function CustomEndpointsSettings({ onConfigSaved, onMainModelChanged }: C
   const [endpoints, setEndpoints] = useState<CustomEndpoint[]>([])
   const [form, setForm] = useState<EndpointForm>(EMPTY_FORM)
   const [discoveredModels, setDiscoveredModels] = useState<string[]>([])
+  // Alias metadata from the last Test; the backend resolves a picked alias to its
+  // canonical model + reasoning effort on Save (#93622).
+  const [discoveredDetails, setDiscoveredDetails] = useState<CustomEndpointModelDetail[]>([])
 
   async function refresh() {
     const data = await getCustomEndpoints()
@@ -137,7 +164,7 @@ export function CustomEndpointsSettings({ onConfigSaved, onMainModelChanged }: C
   async function handleSave() {
     try {
       setSaving(true)
-      const response = await saveCustomEndpoint(toPayload(form, discoveredModels))
+      const response = await saveCustomEndpoint(toPayload(form, discoveredModels, discoveredDetails))
 
       if (!mounted.current) {
         return
@@ -179,6 +206,7 @@ export function CustomEndpointsSettings({ onConfigSaved, onMainModelChanged }: C
       }
 
       setDiscoveredModels(response.models)
+      setDiscoveredDetails(response.model_details ?? [])
 
       if (response.ok) {
         if (!form.model && response.models[0]) {
@@ -256,6 +284,7 @@ export function CustomEndpointsSettings({ onConfigSaved, onMainModelChanged }: C
       if (form.id === endpoint.id) {
         setForm(EMPTY_FORM)
         setDiscoveredModels([])
+        setDiscoveredDetails([])
       }
 
       onConfigSaved?.()
@@ -293,6 +322,7 @@ export function CustomEndpointsSettings({ onConfigSaved, onMainModelChanged }: C
                     onClick={() => {
                       setForm(formFromEndpoint(endpoint))
                       setDiscoveredModels(endpoint.models)
+                      setDiscoveredDetails([])
                     }}
                     type="button"
                   >
@@ -377,6 +407,15 @@ export function CustomEndpointsSettings({ onConfigSaved, onMainModelChanged }: C
                 value={form.baseUrl}
               />
             </label>
+            <fieldset className="grid min-w-0 gap-1.5 text-xs text-muted-foreground">
+              <legend className="mb-1.5">API Mode</legend>
+              <SegmentedControl
+                className="w-full max-w-full"
+                onChange={apiMode => setForm(current => ({ ...current, apiMode }))}
+                options={API_MODE_OPTIONS}
+                value={form.apiMode}
+              />
+            </fieldset>
             <div className="grid gap-3 sm:grid-cols-[minmax(0,1fr)_12rem]">
               <label className="grid gap-1.5 text-xs text-muted-foreground">
                 Default Model
@@ -445,6 +484,7 @@ export function CustomEndpointsSettings({ onConfigSaved, onMainModelChanged }: C
                 onClick={() => {
                   setForm(EMPTY_FORM)
                   setDiscoveredModels([])
+                  setDiscoveredDetails([])
                 }}
                 type="button"
                 variant="ghost"
diff --git a/apps/desktop/src/types/hermes.ts b/apps/desktop/src/types/hermes.ts
index aee88d0367..8190133a49 100644
--- a/apps/desktop/src/types/hermes.ts
+++ b/apps/desktop/src/types/hermes.ts
@@ -221,8 +221,21 @@ export interface MemoryProviderConfig {
   name: string
 }
 
+/** Transport pinned on a custom endpoint; `''` = let the runtime auto-detect. Same
+ * choices as `hermes model`'s custom-provider setup (#93622). */
+export type CustomEndpointApiMode = '' | 'anthropic_messages' | 'chat_completions' | 'codex_responses'
+
+/** One `/v1/models` row; a gateway may advertise a reasoning alias
+ * (`gpt-5.6-sol-high` → `gpt-5.6-sol` @ `high`) that the bare id list flattens. */
+export interface CustomEndpointModelDetail {
+  canonical_model?: null | string
+  id: string
+  reasoning_effort?: null | string
+}
+
 export interface CustomEndpoint {
   api_key_preview?: null | string
+  api_mode?: CustomEndpointApiMode
   base_url: string
   context_length?: null | number
   discover_models: boolean
@@ -248,18 +261,22 @@ export interface CustomEndpointsResponse {
 
 export interface CustomEndpointUpdate {
   api_key?: string
+  api_mode?: CustomEndpointApiMode
   base_url: string
   context_length?: number
   discover_models?: boolean
   id?: string
   make_default?: boolean
   model: string
+  model_details?: CustomEndpointModelDetail[]
   models?: string[]
   name: string
 }
 
 export interface CustomEndpointValidationResponse {
   message: string
+  /** Older backends send only `models`. */
+  model_details?: CustomEndpointModelDetail[]
   models: string[]
   ok: boolean
   reachable: boolean
diff --git a/hermes_cli/web_models.py b/hermes_cli/web_models.py
index 729b44add2..33747afa7c 100644
--- a/hermes_cli/web_models.py
+++ b/hermes_cli/web_models.py
@@ -33,16 +33,27 @@ class MemoryProviderConfigUpdate(BaseModel):
 class MemoryProviderSetupRequest(BaseModel):
     values: Dict[str, Any] = {}
 
+class CustomEndpointModelDetail(BaseModel):
+    """One ``/v1/models`` row with the routing metadata a gateway may advertise on a
+    reasoning alias (``gpt-5.6-sol-high`` → ``gpt-5.6-sol`` @ ``high``). See #93622."""
+    id: str
+    canonical_model: Optional[str] = None
+    reasoning_effort: Optional[str] = None
+
 class CustomEndpointUpdate(BaseModel):
     id: str = ""
     name: str
     base_url: str
     model: str
     api_key: Optional[str] = None
+    # Same choices as the CLI's custom-provider setup; "" = auto-detect at runtime.
+    # None (older UI payload) leaves a hand-written api_mode alone.
+    api_mode: Optional[Literal["", "chat_completions", "codex_responses", "anthropic_messages"]] = None
     context_length: Optional[int] = None
     discover_models: bool = True
     make_default: bool = False
     models: Optional[List[str]] = None
+    model_details: Optional[List[CustomEndpointModelDetail]] = None
 
 class MessagingPlatformUpdate(BaseModel):
     enabled: Optional[bool] = None
diff --git a/hermes_cli/web_routers/config_env.py b/hermes_cli/web_routers/config_env.py
index d53b0e421c..515bb2ef3c 100644
--- a/hermes_cli/web_routers/config_env.py
+++ b/hermes_cli/web_routers/config_env.py
@@ -18,11 +18,11 @@ from hermes_cli.web_server_config import (
     _validated_main_model_selection,
 )
 from hermes_cli.web_server_profiles import (
-    _approval_mode_of, _broadcast_gateway_session_info, _is_other_profile, _parse_model_ids,
+    _approval_mode_of, _broadcast_gateway_session_info, _is_other_profile, _parse_model_entries, _parse_model_ids,
 )
 from fastapi import HTTPException, Request
 from hermes_cli.config import DEFAULT_CONFIG, OPTIONAL_ENV_VARS, read_raw_config, custom_endpoint_key_env, coerce_provider_id, find_provider_entry, get_compatible_custom_providers, redact_key, _deep_merge
-from hermes_cli.config_providers import _custom_provider_entry_to_provider_config
+from hermes_cli.config_providers import _canonical_api_mode, _custom_provider_entry_to_provider_config
 from hermes_cli.web_models import ConfigUpdate, EnvVarUpdate, EnvVarDelete, EnvVarReveal, CustomEndpointUpdate
 from typing import Any, Dict, List, Optional, Tuple
 
@@ -382,6 +382,18 @@ def _config_api_key_is_env_ref(endpoint_id: str) -> bool:
     return bool(isinstance(raw_key, str) and re.search(r"\$\{[^}]+\}", raw_key))
 
 
+_DESKTOP_API_MODES = {"chat_completions", "codex_responses", "anthropic_messages"}
+
+
+def _endpoint_api_mode(entry: Dict[str, Any]) -> str:
+    """The transport a providers entry pins (``api_mode``, or the v12 migration's ``transport``
+    spelling), canonicalized; ``""`` = runtime auto-detect. Mirrors the read order of
+    ``runtime_provider_custom._get_named_custom_provider``."""
+    raw = str(entry.get("api_mode") or entry.get("transport") or "")
+    mode = _canonical_api_mode(raw).lower()
+    return mode if mode in _DESKTOP_API_MODES else ""
+
+
 def _endpoint_row(
     endpoint_id: str, name: str, base_url: str, model: str, models: List[str], context_length,
     discover_models: bool, key_entry: Dict[str, Any], is_current: bool, source: str,
@@ -389,6 +401,7 @@ def _endpoint_row(
     has_api_key, api_key_preview = _api_key_display(key_entry)
     return {
         "id": endpoint_id, "name": name, "base_url": base_url, "model": model, "models": models,
+        "api_mode": _endpoint_api_mode(key_entry),
         "context_length": context_length, "discover_models": discover_models,
         "has_api_key": has_api_key, "api_key_preview": api_key_preview,
         "is_current": is_current, "source": source,
@@ -534,28 +547,65 @@ def _write_custom_endpoint(cfg: Dict[str, Any], body: CustomEndpointUpdate) -> T
 
     # Merge onto the existing entry rather than replacing it: a providers.<name>
     # block can carry hand-written keys the dashboard has no field for
-    # (``api_mode``, ``key_env``/``api_key_env``, ``extra_headers`` — possibly
-    # with credentials — ``request_overrides``); rebuilding from scratch
-    # silently dropped them on an unrelated edit.
+    # (``key_env``/``api_key_env``, ``extra_headers`` — possibly with
+    # credentials — ``request_overrides``); rebuilding from scratch silently
+    # dropped them on an unrelated edit.
     entry: Dict[str, Any] = dict(existing)
     entry.update({
         "name": name, "base_url": base_url, "model": model,
         "discover_models": bool(body.discover_models),
     })
+    # A Responses-only or Anthropic-compatible host 404s on the runtime's
+    # Chat Completions default, so the panel pins the transport the same way
+    # ``hermes model`` does (``api_mode``; the runtime also reads the v12
+    # ``transport`` spelling, so drop it rather than let the two disagree).
+    # ``None`` = older UI payload: keep whatever is hand-written. See #93622.
+    if body.api_mode is not None:
+        entry.pop("transport", None)
+        if body.api_mode:
+            entry["api_mode"] = body.api_mode
+        else:
+            entry.pop("api_mode", None)
     # Same for the model map, so existing models keep their context lengths.
     # ``body.models`` is the catalogue the panel's Test button discovered;
     # without it only the hand-typed model survived Save. A payload with no
     # ``models`` (older UI) still ensures the named default is present.
     # See #69988.
+    details = {d.id.strip(): d for d in (body.model_details or ()) if d.id.strip()}
     existing_models = entry.get("models")
     models_map: Dict[str, Any] = dict(existing_models) if isinstance(existing_models, dict) else {}
-    for candidate in (*(body.models or ()), model):
+    for candidate in (*(body.models or ()), *details, model):
         model_id = str(candidate).strip()
         if not model_id:
             continue
         current = models_map.get(model_id)
-        models_map[model_id] = dict(current) if isinstance(current, dict) else {}
+        row = dict(current) if isinstance(current, dict) else {}
+        detail = details.get(model_id)
+        if detail is not None:
+            # Keep the alias metadata ``/v1/models`` advertised so the catalogue
+            # still says what ``gpt-5.6-sol-high`` stands for after Save.
+            row.update({k: v.strip() for k, v in (("canonical_model", detail.canonical_model),
+                                                  ("reasoning_effort", detail.reasoning_effort)) if v and v.strip()})
+        models_map[model_id] = row
     entry["models"] = models_map
+    # A reasoning alias is not a model the inference route accepts literally:
+    # persist the canonical model and pin its effort through the one runtime
+    # chokepoint (``agent.reasoning_overrides`` → ``resolve_reasoning_config``).
+    alias = details.get(model)
+    canonical = (alias.canonical_model or "").strip() if alias is not None else ""
+    if canonical and canonical != model:
+        from hermes_constants import parse_reasoning_effort
+        effort = (alias.reasoning_effort or "").strip().lower()
+        if parse_reasoning_effort(effort) is not None:
+            agent_cfg = cfg.get("agent") if isinstance(cfg.get("agent"), dict) else {}
+            overrides = agent_cfg.get("reasoning_overrides")
+            overrides = dict(overrides) if isinstance(overrides, dict) else {}
+            overrides[canonical] = effort
+            agent_cfg["reasoning_overrides"] = overrides
+            cfg["agent"] = agent_cfg
+        model = canonical
+        entry["model"] = model
+        models_map.setdefault(model, {})
     if body.context_length and body.context_length > 0:
         entry["context_length"] = int(body.context_length)
         entry["models"][model]["context_length"] = int(body.context_length)
@@ -730,7 +780,11 @@ async def validate_custom_endpoint(body: CustomEndpointUpdate):
     if not resp.is_success:
         return {"ok": False, "reachable": True, "message": f"Endpoint returned HTTP {resp.status_code}.", "models": []}
 
-    return {"ok": True, "reachable": True, "message": "", "models": _parse_model_ids(resp)}
+    # ``models`` stays the bare id list older clients read; ``model_details`` keeps the
+    # alias metadata (``canonical_model`` / ``reasoning_effort``) the id list flattens.
+    entries = _parse_model_entries(resp)
+    return {"ok": True, "reachable": True, "message": "", "models": [e["id"] for e in entries],
+            "model_details": entries}
 
 
 def _endpoint_probe_client(url: str, timeout: float):
diff --git a/hermes_cli/web_server_profiles.py b/hermes_cli/web_server_profiles.py
index 03c7672205..362b162ec5 100644
--- a/hermes_cli/web_server_profiles.py
+++ b/hermes_cli/web_server_profiles.py
@@ -81,9 +81,15 @@ def _broadcast_gateway_session_info() -> None:
         _log.exception("session.info broadcast after config save failed")
 
 
-def _parse_model_ids(resp: "Any") -> List[str]:
-    """Model ids from an OpenAI-compatible ``/v1/models`` response: ``{"data": [{"id": ..}]}``
-    or a bare ``{"data": ["id", ..]}``. ``[]`` on any parse/HTTP error so a slightly
+_MODEL_ENTRY_METADATA = ("canonical_model", "reasoning_effort")
+
+
+def _parse_model_entries(resp: "Any") -> List[Dict[str, str]]:
+    """Model rows from an OpenAI-compatible ``/v1/models`` response as ``{"id": ..}`` dicts,
+    keeping the alias metadata a gateway may advertise (``canonical_model``,
+    ``reasoning_effort``). Flattening to bare ids lost that, so Desktop stored a reasoning
+    alias as the literal upstream model (#93622). Accepts ``{"data": [{"id": ..}]}`` or a
+    bare ``{"data": ["id", ..]}``; ``[]`` on any parse/HTTP error so a slightly
     non-standard endpoint never hard-blocks."""
     try:
         if not resp.is_success:
@@ -94,8 +100,24 @@ def _parse_model_ids(resp: "Any") -> List[str]:
     data = payload.get("data") if isinstance(payload, dict) else payload
     if not isinstance(data, list):
         return []
-    ids = [str((item.get("id") if isinstance(item, dict) else item) or "").strip() for item in data]
-    return [mid for mid in ids if mid]
+    entries: List[Dict[str, str]] = []
+    for item in data:
+        model_id = str((item.get("id") if isinstance(item, dict) else item) or "").strip()
+        if not model_id:
+            continue
+        entry = {"id": model_id}
+        if isinstance(item, dict):
+            for key in _MODEL_ENTRY_METADATA:
+                value = str(item.get(key) or "").strip()
+                if value:
+                    entry[key] = value
+        entries.append(entry)
+    return entries
+
+
+def _parse_model_ids(resp: "Any") -> List[str]:
+    """Bare model ids from a ``/v1/models`` response (see :func:`_parse_model_entries`)."""
+    return [entry["id"] for entry in _parse_model_entries(resp)]
 
 
 def _fallback_profile_entry(profiles_mod, name: str, home: Path, *, is_default: bool,
diff --git a/tests/hermes_cli/test_web_server.py b/tests/hermes_cli/test_web_server.py
index 148909e587..d342e01de1 100644
--- a/tests/hermes_cli/test_web_server.py
+++ b/tests/hermes_cli/test_web_server.py
@@ -2061,6 +2061,89 @@ class TestWebServerEndpoints:
         assert "sk-super-secret" not in yaml.safe_dump(cfg)
 
 
+    def test_custom_endpoint_save_pins_api_mode_and_resolves_reasoning_alias(self):
+        """Desktop's Custom Endpoints form pins the transport and keeps alias metadata (#93622).
+
+        A Responses-only host 404s on the runtime's Chat Completions default, so the chosen
+        ``api_mode`` must land on the providers entry and read back; a discovered reasoning
+        alias resolves to its canonical model + ``agent.reasoning_overrides`` instead of being
+        saved as a literal upstream model id.
+        """
+        from hermes_cli.config import load_config
+
+        response = self.client.post(
+            "/api/providers/custom-endpoints",
+            json={
+                "id": "custom-responses", "name": "custom-responses",
+                "base_url": "https://responses-gateway.example.com/v1",
+                "model": "gpt-5.6-sol-high", "api_mode": "codex_responses", "make_default": True,
+                "models": ["gpt-5.6-sol", "gpt-5.6-sol-high"],
+                "model_details": [
+                    {"id": "gpt-5.6-sol"},
+                    {"id": "gpt-5.6-sol-high", "canonical_model": "gpt-5.6-sol", "reasoning_effort": "high"},
+                ],
+            },
+        )
+        assert response.status_code == 200
+        row = next(e for e in response.json()["endpoints"] if e["id"] == "custom-responses")
+        assert row["api_mode"] == "codex_responses"
+        assert row["model"] == "gpt-5.6-sol"
+
+        cfg = load_config()
+        entry = cfg["providers"]["custom-responses"]
+        assert entry["api_mode"] == "codex_responses"
+        assert entry["model"] == "gpt-5.6-sol"
+        assert entry["models"]["gpt-5.6-sol-high"] == {"canonical_model": "gpt-5.6-sol", "reasoning_effort": "high"}
+        assert cfg["model"]["default"] == "gpt-5.6-sol"
+        assert cfg["agent"]["reasoning_overrides"]["gpt-5.6-sol"] == "high"
+
+        # An older UI payload (no api_mode) leaves the pinned transport alone; "" clears it.
+        self.client.post("/api/providers/custom-endpoints", json={
+            "id": "custom-responses", "name": "custom-responses",
+            "base_url": "https://responses-gateway.example.com/v1", "model": "gpt-5.6-sol"})
+        assert load_config()["providers"]["custom-responses"]["api_mode"] == "codex_responses"
+        self.client.post("/api/providers/custom-endpoints", json={
+            "id": "custom-responses", "name": "custom-responses", "api_mode": "",
+            "base_url": "https://responses-gateway.example.com/v1", "model": "gpt-5.6-sol"})
+        listed = self.client.get("/api/providers/custom-endpoints").json()["endpoints"]
+        assert next(e for e in listed if e["id"] == "custom-responses")["api_mode"] == ""
+        assert "api_mode" not in load_config()["providers"]["custom-responses"]
+
+    def test_custom_endpoint_validate_keeps_model_alias_metadata(self, monkeypatch):
+        """``validate`` returns the bare id list older clients read AND ``model_details`` with
+        the ``canonical_model`` / ``reasoning_effort`` a gateway advertises (#93622)."""
+        import contextlib
+
+        from hermes_cli.web_routers import config_env
+
+        class FakeResp:
+            status_code = 200
+            is_success = True
+
+            def json(self):
+                return {"data": [
+                    {"id": "gpt-5.6-sol", "object": "model"},
+                    {"id": "gpt-5.6-sol-high", "canonical_model": "gpt-5.6-sol", "reasoning_effort": "high"},
+                ]}
+
+        class FakeClient:
+            async def get(self, url, headers=None):
+                return FakeResp()
+
+        @contextlib.asynccontextmanager
+        async def fake_probe_client(url, timeout):
+            yield FakeClient()
+
+        monkeypatch.setattr(config_env, "_endpoint_probe_client", fake_probe_client)
+        body = self.client.post("/api/providers/custom-endpoints/validate", json={
+            "name": "x", "base_url": "https://responses-gateway.example.com/v1", "model": ""}).json()
+        assert body["ok"] is True
+        assert body["models"] == ["gpt-5.6-sol", "gpt-5.6-sol-high"]
+        assert body["model_details"] == [
+            {"id": "gpt-5.6-sol"},
+            {"id": "gpt-5.6-sol-high", "canonical_model": "gpt-5.6-sol", "reasoning_effort": "high"},
+        ]
+
     def test_custom_endpoint_save_leaves_a_hand_written_env_ref_alone(self, monkeypatch):
         """``api_key: ${MY_KEY}`` is already safe — don't copy it elsewhere.
 
@@ -5243,6 +5326,7 @@ class TestValidateProviderCredential:
             "reachable": True,
             "message": "",
             "models": ["local-model"],
+            "model_details": [{"id": "local-model"}],
         }
         assert captured == {
             "url": "http://localhost:8000/v1/models",
diff --git a/website/docs/user-guide/desktop.md b/website/docs/user-guide/desktop.md
index 65bfbaf62c..4657aded11 100644
--- a/website/docs/user-guide/desktop.md
+++ b/website/docs/user-guide/desktop.md
@@ -194,6 +194,7 @@ Manage providers, models, tools, and credentials from a real UI instead of editi
 
 - **Providers settings pane** — a dedicated place to manage inference providers, with an Accounts / API-keys UX for signing in and storing credentials per provider. Accounts and API keys share the Settings **Applies to** selection: credential reads and edits, OAuth account removal, and sign-in launched here target the selected profile, not the active chat profile. The sign-in flow keeps that target through credential saving and model selection. Changing **Applies to** discards unsaved credential drafts. Closing sign-in cancels polling and ignores late results; a credential write already sent may still finish in its original profile. Externally managed CLI credentials use their own CLI and are not covered by this profile selector. Its **Local Models** view installs and manages an on-device llama.cpp runtime — see [Local Models](./local-models.md).
 - **Every provider and model in the menus** — the GUI surfaces the full provider list and every model that `hermes model` knows about, so you pick from the same catalog the CLI sees rather than a curated subset.
+- **Custom endpoints with an API mode** — **Settings → Providers → Custom Endpoints** has an **API Mode** selector (**Auto-detect**, **Chat Completions**, **Responses API**, **Anthropic Messages**) — the same choice `hermes model` offers for a custom provider. It is saved as `providers.<id>.api_mode` in `config.yaml`, so a Responses-only or Anthropic-compatible host is no longer called on `/chat/completions`. **Test** also keeps the alias metadata a gateway advertises in `/v1/models` (`canonical_model`, `reasoning_effort`): picking an alias such as `gpt-5.6-sol-high` saves the canonical model and pins its effort under `agent.reasoning_overrides`.
 - **xAI Grok OAuth** — Grok is a first-class OAuth provider in the launcher; sign in through the browser flow like the other OAuth providers.
 - **Tool-backend installs from the GUI** — run a tool backend's post-setup install steps directly from the app instead of dropping to a terminal. In the terminal backend picker, selecting a backend marked **Needs setup** asks for confirmation first; declining leaves the current backend selected.
 - **Terminal font picker** — choose an installed font in **Settings → Appearance**. Nerd Fonts such as `MesloLGS NF` render Powerlevel10k separators and icons in both interactive and agent terminals; the setting is saved per profile.