diff --git a/tests/test_custom_provider_display_name.py b/tests/test_custom_provider_display_name.py
index fca1842..f8c1771 100644
--- a/tests/test_custom_provider_display_name.py
+++ b/tests/test_custom_provider_display_name.py
@@ -5,9 +5,24 @@ When a custom_providers entry carries a `name` field (e.g. "Agent37"), the
 web UI model picker should show that name as the group header rather than the
 generic "Custom" label.
 """
+import pytest
 import api.config as config
 
 
+@pytest.fixture(autouse=True)
+def _isolate_models_cache():
+    """Invalidate the models TTL cache before and after every test in this file."""
+    try:
+        config.invalidate_models_cache()
+    except Exception:
+        pass
+    yield
+    try:
+        config.invalidate_models_cache()
+    except Exception:
+        pass
+
+
 def _models_with_cfg(model_cfg=None, custom_providers=None, active_provider=None):
     """Temporarily patch config.cfg, call get_available_models(), restore.
 
diff --git a/tests/test_issue644.py b/tests/test_issue644.py
index 6cd4df2..73ba5b3 100644
--- a/tests/test_issue644.py
+++ b/tests/test_issue644.py
@@ -3,6 +3,20 @@ import pytest
 import api.config as _cfg
 
 
+@pytest.fixture(autouse=True)
+def _isolate_models_cache():
+    """Invalidate the models TTL cache before and after every test in this file."""
+    try:
+        _cfg.invalidate_models_cache()
+    except Exception:
+        pass
+    yield
+    try:
+        _cfg.invalidate_models_cache()
+    except Exception:
+        pass
+
+
 def _available_models_with_cfg(cfg_override):
     """Helper: temporarily patch config.cfg, call get_available_models(), restore."""
     old_cfg = dict(_cfg.cfg)
diff --git a/tests/test_minimax_provider.py b/tests/test_minimax_provider.py
index 27c594d..c483786 100644
--- a/tests/test_minimax_provider.py
+++ b/tests/test_minimax_provider.py
@@ -8,9 +8,24 @@ Covers:
   - minimax/MiniMax-M2.7 (slash format) is routed via openrouter when active provider differs
 """
 import os
+import pytest
 import api.config as config
 
 
+@pytest.fixture(autouse=True)
+def _isolate_models_cache():
+    """Invalidate the models TTL cache before and after every test in this file."""
+    try:
+        config.invalidate_models_cache()
+    except Exception:
+        pass
+    yield
+    try:
+        config.invalidate_models_cache()
+    except Exception:
+        pass
+
+
 # ── Helper ────────────────────────────────────────────────────────────────────
 
 def _resolve_with_config(model_id, provider=None, base_url=None):
diff --git a/tests/test_model_resolver.py b/tests/test_model_resolver.py
index f6958f9..4f1ca53 100644
--- a/tests/test_model_resolver.py
+++ b/tests/test_model_resolver.py
@@ -3,6 +3,7 @@ Tests for resolve_model_provider() model routing logic.
 Verifies that model IDs are correctly resolved to (model, provider, base_url)
 tuples for different provider configurations.
 """
+import pytest
 import api.config as config
 
 
@@ -160,6 +161,30 @@ def test_custom_provider_model_with_slash_routes_to_named_custom_provider():
 
 # ── get_available_models() @provider: hint behaviour ──────────────────────
 
+
+@pytest.fixture(autouse=True)
+def _isolate_models_cache():
+    """Invalidate the models TTL cache before and after every test in this file.
+
+    Several helpers here mutate ``config.cfg`` in-memory and call
+    ``get_available_models()``.  Without this guard, a prior test that called
+    ``get_available_models()`` leaves a 60-second TTL cache entry; the next
+    test that mutates cfg and calls the function gets a cache hit instead of
+    running the function body, causing silently wrong results (e.g. the
+    ``test_custom_endpoint_uses_model_config_api_key_for_model_discovery``
+    ``KeyError: 'auth'`` on CI where ``urlopen`` is never reached).
+    """
+    try:
+        config.invalidate_models_cache()
+    except Exception:
+        pass
+    yield
+    try:
+        config.invalidate_models_cache()
+    except Exception:
+        pass
+
+
 def _available_models_with_provider(provider):
     """Helper: temporarily set active_provider in config."""
     old_cfg = dict(config.cfg)
diff --git a/tests/test_opencode_providers.py b/tests/test_opencode_providers.py
index 7880b7d..33303d4 100644
--- a/tests/test_opencode_providers.py
+++ b/tests/test_opencode_providers.py
@@ -6,9 +6,24 @@ env-var fallback detection.
 import os
 import sys
 import types
+import pytest
 import api.config as config
 
 
+@pytest.fixture(autouse=True)
+def _isolate_models_cache():
+    """Invalidate the models TTL cache before and after every test in this file."""
+    try:
+        config.invalidate_models_cache()
+    except Exception:
+        pass
+    yield
+    try:
+        config.invalidate_models_cache()
+    except Exception:
+        pass
+
+
 # ── Provider registration ─────────────────────────────────────────────
 
 def test_opencode_zen_in_provider_display():