diff --git a/src/ai_client.py b/src/ai_client.py
index 473a8f03..f7dcbe3a 100644
--- a/src/ai_client.py
+++ b/src/ai_client.py
@@ -51,8 +51,11 @@ from src.models       import ToolPreset, BiasProfile, Tool
 from src.paths        import get_credentials_path
 from src.tool_bias    import ToolBiasEngine
 from src.tool_presets import ToolPresetManager
+from src.tool_presets import ToolPresetManager
 
+PROVIDERS: List[str] = ["gemini", "anthropic", "gemini_cli", "deepseek", "minimax", "qwen", "grok", "llama"]
 
+# _require_warmed lives
 # _require_warmed lives in src/module_loader.py to avoid duplicating the
 # lookup logic across files that need heavy modules. Re-exported here so
 # existing call sites and the T3.1 test (which asserts
diff --git a/src/models.py b/src/models.py
index 53735156..4aec68d1 100644
--- a/src/models.py
+++ b/src/models.py
@@ -53,7 +53,14 @@ from src.paths      import get_config_path
 
 #region: Constants
 
-PROVIDERS: List[str] = ["gemini", "anthropic", "gemini_cli", "deepseek", "minimax", "qwen", "grok", "llama"]
+# PROVIDERS is the source of truth in src/ai_client.py (per the
+# follow-up track's Naming Convention HARD RULE). Lazy-loaded
+# via the __getattr__ defined later in this module to break the
+# circular import (src.ai_client imports ToolPreset/BiasProfile/
+# Tool from this module at line 50, so a top-level 'from
+# src.ai_client import PROVIDERS' here would deadlock). The
+# audit script scripts/audit_providers_source_of_truth.py
+# verifies PROVIDERS is declared in src/ai_client.py and not here.
 
 AGENT_TOOL_NAMES: List[str] = [
  "run_powershell",
@@ -251,6 +258,9 @@ _PYDANTIC_CLASS_FACTORIES: dict[str, callable] = {
 }
 
 def __getattr__(name: str) -> Any:
+ if name == "PROVIDERS":
+  from src.ai_client import PROVIDERS as _PROVIDERS
+  return _PROVIDERS
  if name in _PYDANTIC_CLASS_FACTORIES:
   cls = _PYDANTIC_CLASS_FACTORIES[name]()
   globals()[name] = cls
diff --git a/tests/test_provider_curation.py b/tests/test_provider_curation.py
index 319c9ccc..a9948f8e 100644
--- a/tests/test_provider_curation.py
+++ b/tests/test_provider_curation.py
@@ -3,6 +3,6 @@ import src.app_controller
 
 def test_providers_moved_to_models():
  """Verify that PROVIDERS list is in models.py and removed from AppController."""
- expected_providers = ['gemini', 'anthropic', 'gemini_cli', 'deepseek', 'minimax']
+ expected_providers = ['gemini', 'anthropic', 'gemini_cli', 'deepseek', 'minimax', 'qwen', 'grok', 'llama']
  assert models.PROVIDERS == expected_providers
  assert not hasattr(src.app_controller.AppController, 'PROVIDERS')
\ No newline at end of file
diff --git a/tests/test_providers_source_of_truth.py b/tests/test_providers_source_of_truth.py
new file mode 100644
index 00000000..91609d1d
--- /dev/null
+++ b/tests/test_providers_source_of_truth.py
@@ -0,0 +1,23 @@
+"""Verify PROVIDERS is defined in src.ai_client (the source of truth)
+and re-exported from src.models (backward compat shim).
+
+Per the follow-up track's Naming Convention (HARD RULE), PROVIDERS
+lives in src/ai_client.py. src/models.py keeps a re-export
+shim so existing import sites don't break.
+"""
+from __future__ import annotations
+import src.models as models
+import src.ai_client as ai_client
+
+EXPECTED_PROVIDERS = ["gemini", "anthropic", "gemini_cli", "deepseek", "minimax", "qwen", "grok", "llama"]
+
+def test_providers_defined_in_src_ai_client() -> None:
+ assert hasattr(ai_client, "PROVIDERS")
+ assert ai_client.PROVIDERS == EXPECTED_PROVIDERS
+
+def test_providers_reexported_from_src_models() -> None:
+ assert hasattr(models, "PROVIDERS")
+ assert models.PROVIDERS == EXPECTED_PROVIDERS
+
+def test_providers_same_object_in_both_modules() -> None:
+ assert models.PROVIDERS is ai_client.PROVIDERS