diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa800554..ee1f6913 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@
 
 ### Fixed
 
+- **Models from a user-defined provider in `config.yaml` now route correctly.** If you defined a custom provider under the `providers:` block with an explicit `models:` allowlist, a bare model id from that list wasn't matched by request-time routing — it silently fell back to the default provider and often 404'd. Resolution now scans your `providers:` allowlists (exact match, same as `custom_providers:`), so those models reach the right endpoint. Copilot is deliberately excluded from this scan because `providers.copilot.models` is a per-model settings map (reasoning effort, limits), not a routing allowlist. Thanks @akay64. (#5511)
 - **The transcript no longer scrolls up when the composer grows.** When you were pinned to the bottom of a conversation and the composer got taller — multi-line typing, `Shift+Enter`, or a multi-line / dictation paste — the transcript viewport shrank by the same amount and left you stranded a row or two above the bottom (it read as the chat "randomly scrolling up" during normal use). The transcript now re-pins to the bottom whenever the composer grows, but only when you were genuinely still pinned there — if you'd scrolled up to read history, nothing yanks you back down. (#5516, #5514, #5515)
 - **A deleted conversation no longer comes back as a read-only "ghost" after a restart.** Deleting a WebUI session removed its file but left a recoverable row in the agent's state database, so after a server restart and page reload the deleted conversation could reappear as a read-only "Agent" session still showing its old transcript. Deleted WebUI sessions are now recorded in a durable tombstone that the sidebar projection, startup backup-recovery, audit, and session-claim paths all honor, so a deleted session stays gone (the backend keeps returning the 404 the client relies on to clear the stale route). Genuine crash recovery is unaffected — a session whose sidecar is lost without a delete is still restored — imported external-channel (messaging) sessions are exempt and keep their transcript, and a deleted id is automatically un-tombstoned if the same session is later re-created or re-imported. Thanks @rodboev. (#5504, #5498)
 - **A drag that ends over the sidebar no longer switches conversations by accident.** Releasing the mouse (a stray `pointerup`) over a session row after a drag that began elsewhere in the main content area could switch you into that conversation unintentionally. Session switching now ignores a `pointerup` that isn't a genuine click on the row. Thanks @webtecnica. (#5487, #5462)
diff --git a/api/config.py b/api/config.py
index 712dff59..346e6525 100644
--- a/api/config.py
+++ b/api/config.py
@@ -2572,6 +2572,13 @@ def resolve_model_provider(model_id: str) -> tuple:
         for slug, pdef in providers_cfg.items():
             if not isinstance(pdef, dict):
                 continue
+            # Copilot is the documented exception: `providers.copilot.models` is
+            # a per-model SETTINGS map (reasoning_effort, limits, etc.), NOT a
+            # routable allowlist (see the exception at the catalog-build site).
+            # Scanning it here would let a Copilot per-model settings entry
+            # hijack that model's routing away from its real provider (#5511).
+            if _canonicalise_provider_id(slug) == "copilot":
+                continue
             p_models = pdef.get('models')
             if isinstance(p_models, list):
                 for m in p_models:
diff --git a/tests/test_model_resolver.py b/tests/test_model_resolver.py
index df80b94c..740ef176 100644
--- a/tests/test_model_resolver.py
+++ b/tests/test_model_resolver.py
@@ -748,3 +748,68 @@ def test_bare_custom_provider_no_base_url_with_known_prefix_keeps_custom_and_ful
     )
     assert model == 'google/gemma-2-9b'
     assert base_url is None
+
+
+# ── providers: (config.yaml user-defined provider) scan (#5511) ─────────────
+
+def _resolve_with_providers(model_id, providers_cfg, *, provider=None, default=None):
+    """Helper: temporarily set config.cfg['providers'] + model, call resolve, restore."""
+    old_cfg = dict(config.cfg)
+    model_cfg = {}
+    if provider:
+        model_cfg['provider'] = provider
+    if default:
+        model_cfg['default'] = default
+    config.cfg['model'] = model_cfg
+    config.cfg['providers'] = providers_cfg
+    try:
+        return config.resolve_model_provider(model_id)
+    finally:
+        config.cfg.clear()
+        config.cfg.update(old_cfg)
+
+
+def test_providers_scan_routes_user_defined_allowlist_5511():
+    """A user-defined providers.<slug>.models allowlist routes a bare model id
+    to that provider (the feature #5511 adds)."""
+    model, provider, base_url = _resolve_with_providers(
+        'my-model-1',
+        {'myprov': {'base_url': 'https://my.example/v1', 'models': ['my-model-1', 'my-model-2']}},
+        provider='openai',
+        default='gpt-5',
+    )
+    assert provider == 'myprov', f"user-defined provider allowlist must route; got {provider!r}"
+    assert model == 'my-model-1'
+    assert base_url == 'https://my.example/v1'
+
+
+def test_providers_scan_skips_copilot_settings_map_5511():
+    """providers.copilot.models is a per-model SETTINGS map, NOT a routable
+    allowlist — a Copilot per-model settings entry must NOT hijack routing away
+    from the model's real provider (#5511 gate-cert CORE finding)."""
+    model, provider, base_url = _resolve_with_providers(
+        'gpt-5',
+        {'copilot': {'models': {'gpt-5': {'reasoning_effort': 'high'}}}},
+        provider='openai',
+        default='gpt-5',
+    )
+    assert provider == 'openai', (
+        "Copilot settings-map entry must NOT hijack routing; "
+        f"gpt-5 must stay on openai, got {provider!r}"
+    )
+    assert model == 'gpt-5'
+
+
+def test_providers_scan_copilot_list_shape_also_skipped_5511():
+    """Defense in depth: even if providers.copilot.models is a list shape, the
+    Copilot exclusion still prevents a routing hijack."""
+    model, provider, base_url = _resolve_with_providers(
+        'gpt-5',
+        {'copilot': {'models': ['gpt-5', 'gpt-5-mini']}},
+        provider='openai',
+        default='gpt-5',
+    )
+    assert provider == 'openai', (
+        f"Copilot (list shape) must not hijack routing; got {provider!r}"
+    )
+    assert model == 'gpt-5'