diff --git a/apps/desktop/src/app/session/hooks/use-model-controls.test.tsx b/apps/desktop/src/app/session/hooks/use-model-controls.test.tsx
index 8f52018982a..612290800e0 100644
--- a/apps/desktop/src/app/session/hooks/use-model-controls.test.tsx
+++ b/apps/desktop/src/app/session/hooks/use-model-controls.test.tsx
@@ -1,5 +1,5 @@
-import { renderHook } from '@testing-library/react'
 import { QueryClient } from '@tanstack/react-query'
+import { cleanup, render, renderHook } from '@testing-library/react'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
 import { getGlobalModelInfo } from '@/hermes'
@@ -13,12 +13,51 @@ import {
 
 import { useModelControls } from './use-model-controls'
 
+const setGlobalModel = vi.fn()
+const notifyError = vi.fn()
+
 vi.mock('@/hermes', () => ({
   getGlobalModelInfo: vi.fn(),
-  setGlobalModel: vi.fn()
+  setGlobalModel: (...args: Parameters<typeof setGlobalModel>) => setGlobalModel(...args)
 }))
 
-describe('useModelControls.refreshCurrentModel', () => {
+vi.mock('@/i18n', () => ({
+  useI18n: () => ({
+    t: {
+      desktop: {
+        modelSwitchFailed: 'Model switch failed'
+      }
+    }
+  })
+}))
+
+vi.mock('@/store/notifications', () => ({
+  notifyError: (...args: Parameters<typeof notifyError>) => notifyError(...args)
+}))
+
+type Controls = ReturnType<typeof useModelControls>
+
+function Harness({
+  activeSessionId,
+  onReady,
+  requestGateway
+}: {
+  activeSessionId: string | null
+  onReady: (controls: Controls) => void
+  requestGateway: <T = unknown>(method: string, params?: Record<string, unknown>) => Promise<T>
+}) {
+  const controls = useModelControls({
+    activeSessionId,
+    queryClient: new QueryClient(),
+    requestGateway
+  })
+
+  onReady(controls)
+
+  return null
+}
+
+describe('useModelControls', () => {
   beforeEach(() => {
     $activeSessionId.set(null)
     setCurrentModel('')
@@ -26,6 +65,7 @@ describe('useModelControls.refreshCurrentModel', () => {
   })
 
   afterEach(() => {
+    cleanup()
     vi.restoreAllMocks()
     $activeSessionId.set(null)
     setCurrentModel('')
@@ -74,4 +114,55 @@ describe('useModelControls.refreshCurrentModel', () => {
     expect($currentModel.get()).toBe('deepseek/deepseek-v4-pro')
     expect($currentProvider.get()).toBe('deepseek')
   })
+
+  it('routes active-session picker changes through config.set with an explicit provider', async () => {
+    const requestGateway = vi.fn(async () => ({ key: 'model', value: 'claude-sonnet-4.6' }) as never)
+    let controls!: Controls
+
+    render(
+      <Harness
+        activeSessionId="session-1"
+        onReady={value => (controls = value)}
+        requestGateway={requestGateway}
+      />
+    )
+
+    await expect(
+      controls.selectModel({
+        model: 'claude-sonnet-4.6',
+        persistGlobal: false,
+        provider: 'anthropic'
+      })
+    ).resolves.toBe(true)
+
+    expect(requestGateway).toHaveBeenCalledWith('config.set', {
+      session_id: 'session-1',
+      key: 'model',
+      value: 'claude-sonnet-4.6 --provider anthropic'
+    })
+    expect(requestGateway).not.toHaveBeenCalledWith('slash.exec', expect.anything())
+  })
+
+  it('keeps the global path on setGlobalModel when there is no active session', async () => {
+    setGlobalModel.mockResolvedValue(undefined)
+    let controls!: Controls
+
+    render(
+      <Harness
+        activeSessionId={null}
+        onReady={value => (controls = value)}
+        requestGateway={vi.fn()}
+      />
+    )
+
+    await expect(
+      controls.selectModel({
+        model: 'claude-sonnet-4.6',
+        persistGlobal: false,
+        provider: 'anthropic'
+      })
+    ).resolves.toBe(true)
+
+    expect(setGlobalModel).toHaveBeenCalledWith('anthropic', 'claude-sonnet-4.6')
+  })
 })
diff --git a/apps/desktop/src/app/session/hooks/use-model-controls.ts b/apps/desktop/src/app/session/hooks/use-model-controls.ts
index 525c8d8385b..681eac871a2 100644
--- a/apps/desktop/src/app/session/hooks/use-model-controls.ts
+++ b/apps/desktop/src/app/session/hooks/use-model-controls.ts
@@ -82,9 +82,10 @@ export function useModelControls({ activeSessionId, queryClient, requestGateway
 
       try {
         if (activeSessionId) {
-          await requestGateway('slash.exec', {
+          await requestGateway('config.set', {
             session_id: activeSessionId,
-            command: `/model ${selection.model} --provider ${selection.provider}${selection.persistGlobal ? ' --global' : ''}`
+            key: 'model',
+            value: `${selection.model} --provider ${selection.provider}${selection.persistGlobal ? ' --global' : ''}`
           })
 
           if (selection.persistGlobal) {
diff --git a/tests/test_tui_gateway_server.py b/tests/test_tui_gateway_server.py
index 90a7f200255..da85cc26ad6 100644
--- a/tests/test_tui_gateway_server.py
+++ b/tests/test_tui_gateway_server.py
@@ -3036,6 +3036,94 @@ def test_config_set_model_global_persists(monkeypatch):
     assert saved["model"]["base_url"] == "https://api.anthropic.com"
 
 
+def test_config_set_model_explicit_provider_skips_broken_default_init(monkeypatch):
+    seen = {"build": 0, "wait": 0, "requested": []}
+    session = _session()
+    session["agent"] = None
+    server._sessions["sid"] = session
+    monkeypatch.setattr(server, "_load_cfg", lambda: {"model": {"default": "broken/model", "provider": "openrouter"}})
+    monkeypatch.setattr(server, "_start_agent_build", lambda *_args: seen.__setitem__("build", seen["build"] + 1))
+    monkeypatch.setattr(server, "_wait_agent", lambda *_args: seen.__setitem__("wait", seen["wait"] + 1))
+    monkeypatch.setattr(server, "_emit", lambda *args, **kwargs: None)
+    monkeypatch.setattr(server, "_restart_slash_worker", lambda *args, **kwargs: None)
+
+    def fake_runtime_provider(*, requested=None, target_model=None, **_kwargs):
+        seen["requested"].append((requested, target_model))
+        if requested is None:
+            raise RuntimeError("broken default provider should not be initialized")
+        if requested == "anthropic":
+            return {
+                "api_key": "sk-anthropic",
+                "api_mode": "anthropic_messages",
+                "base_url": "https://api.anthropic.com",
+            }
+        raise RuntimeError(f"unexpected provider {requested}")
+
+    monkeypatch.setattr("hermes_cli.runtime_provider.resolve_runtime_provider", fake_runtime_provider)
+
+    try:
+        resp = server.handle_request(
+            {
+                "id": "1",
+                "method": "config.set",
+                "params": {
+                    "session_id": "sid",
+                    "key": "model",
+                    "value": "claude-sonnet-4.6 --provider anthropic",
+                },
+            }
+        )
+
+        assert resp["result"]["value"] == "claude-sonnet-4-6"
+        assert seen["build"] == 0
+        assert seen["wait"] == 0
+        assert seen["requested"] == [("anthropic", "claude-sonnet-4.6")]
+        assert session["model_override"]["provider"] == "anthropic"
+        assert session["model_override"]["model"] == "claude-sonnet-4-6"
+    finally:
+        server._sessions.pop("sid", None)
+
+
+def test_config_set_model_explicit_provider_surfaces_selected_provider_errors(monkeypatch):
+    seen = {"build": 0, "wait": 0}
+    session = _session()
+    session["agent"] = None
+    server._sessions["sid"] = session
+    monkeypatch.setattr(server, "_load_cfg", lambda: {"model": {"default": "broken/model", "provider": "openrouter"}})
+    monkeypatch.setattr(server, "_start_agent_build", lambda *_args: seen.__setitem__("build", seen["build"] + 1))
+    monkeypatch.setattr(server, "_wait_agent", lambda *_args: seen.__setitem__("wait", seen["wait"] + 1))
+
+    def fake_runtime_provider(*, requested=None, **_kwargs):
+        if requested is None:
+            raise RuntimeError("broken default provider should not be initialized")
+        if requested == "anthropic":
+            raise RuntimeError("missing anthropic API key")
+        raise RuntimeError(f"unexpected provider {requested}")
+
+    monkeypatch.setattr("hermes_cli.runtime_provider.resolve_runtime_provider", fake_runtime_provider)
+
+    try:
+        resp = server.handle_request(
+            {
+                "id": "1",
+                "method": "config.set",
+                "params": {
+                    "session_id": "sid",
+                    "key": "model",
+                    "value": "claude-sonnet-4.6 --provider anthropic",
+                },
+            }
+        )
+
+        assert resp["error"]["code"] == 5001
+        assert "anthropic" in resp["error"]["message"].lower()
+        assert "missing anthropic api key" in resp["error"]["message"].lower()
+        assert seen["build"] == 0
+        assert seen["wait"] == 0
+    finally:
+        server._sessions.pop("sid", None)
+
+
 def test_config_set_model_does_not_leak_inference_provider_env(monkeypatch):
     """A /model switch must NOT mutate process-global env vars. The desktop /
     dashboard tui_gateway backend hosts every same-profile session in one
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index d34f558f6cf..715ca8b48b6 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -1961,11 +1961,14 @@ def _apply_model_switch(
     *,
     confirm_expensive_model: bool = False,
     pin_session_override: bool = True,
+    parsed_flags: tuple[str, str, bool, bool] | None = None,
 ) -> dict:
     from hermes_cli.model_switch import parse_model_flags, switch_model
     from hermes_cli.runtime_provider import resolve_runtime_provider
 
-    model_input, explicit_provider, persist_global, _force_refresh = parse_model_flags(raw_input)
+    if parsed_flags is None:
+        parsed_flags = parse_model_flags(raw_input)
+    model_input, explicit_provider, persist_global, _force_refresh = parsed_flags
     if not model_input:
         raise ValueError("model value required")
 
@@ -1976,20 +1979,24 @@ def _apply_model_switch(
         current_base_url = getattr(agent, "base_url", "") or ""
         current_api_key = getattr(agent, "api_key", "") or ""
     else:
-        runtime = resolve_runtime_provider(requested=None)
-        current_provider = str(runtime.get("provider", "") or "")
         current_model = _resolve_model()
-        current_base_url = str(runtime.get("base_url", "") or "")
-        # Preserve a callable api_key (Azure Foundry Entra ID bearer
-        # provider) unchanged — ``str(...)`` would produce
-        # ``"<function ...>"`` and poison downstream switch_model
-        # validation. Match the agent-present branch's behavior at the
-        # top of this block.
-        _runtime_key = runtime.get("api_key", "")
-        if callable(_runtime_key) and not isinstance(_runtime_key, str):
-            current_api_key = _runtime_key
-        else:
-            current_api_key = str(_runtime_key or "")
+        current_provider = explicit_provider.strip()
+        current_base_url = ""
+        current_api_key = ""
+        if not explicit_provider:
+            runtime = resolve_runtime_provider(requested=None)
+            current_provider = str(runtime.get("provider", "") or "")
+            current_base_url = str(runtime.get("base_url", "") or "")
+            # Preserve a callable api_key (Azure Foundry Entra ID bearer
+            # provider) unchanged — ``str(...)`` would produce
+            # ``"<function ...>"`` and poison downstream switch_model
+            # validation. Match the agent-present branch's behavior at the
+            # top of this block.
+            _runtime_key = runtime.get("api_key", "")
+            if callable(_runtime_key) and not isinstance(_runtime_key, str):
+                current_api_key = _runtime_key
+            else:
+                current_api_key = str(_runtime_key or "")
 
     # Load user-defined providers so switch_model can resolve named custom
     # endpoints (e.g. "ollama-launch") and validate against saved model lists.
@@ -6996,7 +7003,11 @@ def _(rid, params: dict) -> dict:
                         4009,
                         "session busy — /interrupt the current turn before switching models",
                     )
-                if session.get("agent") is None:
+                from hermes_cli.model_switch import parse_model_flags
+
+                parsed_flags = parse_model_flags(value)
+                _model_input, explicit_provider, _persist_global, _force_refresh = parsed_flags
+                if session.get("agent") is None and not explicit_provider.strip():
                     session_id = params.get("session_id", "")
                     _start_agent_build(session_id, session)
                     init_err = _wait_agent(session, rid)
@@ -7011,6 +7022,7 @@ def _(rid, params: dict) -> dict:
                     confirm_expensive_model=bool(
                         params.get("confirm_expensive_model", False)
                     ),
+                    parsed_flags=parsed_flags,
                 )
             else:
                 result = _apply_model_switch(