diff --git a/litellm/model_prices_and_context_window_backup.json b/litellm/model_prices_and_context_window_backup.json
index de6c8f33f75..c420ec93167 100644
--- a/litellm/model_prices_and_context_window_backup.json
+++ b/litellm/model_prices_and_context_window_backup.json
@@ -28199,7 +28199,7 @@
         "output_cost_per_token": 1.5e-05,
         "output_cost_per_token_above_200k_tokens": 2.25e-05,
         "source": "https://openrouter.ai/anthropic/claude-sonnet-4.6",
-        "supports_assistant_prefill": true,
+        "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
         "supports_prompt_caching": true,
@@ -28237,7 +28237,7 @@
         "max_tokens": 128000,
         "mode": "chat",
         "output_cost_per_token": 2.5e-05,
-        "supports_assistant_prefill": true,
+        "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
         "supports_prompt_caching": true,
@@ -33453,7 +33453,7 @@
         "max_tokens": 64000,
         "mode": "chat",
         "output_cost_per_token": 2.5e-05,
-        "supports_assistant_prefill": true,
+        "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
         "supports_prompt_caching": true,
diff --git a/model_prices_and_context_window.json b/model_prices_and_context_window.json
index c1a2494fbdc..deeace3fa82 100644
--- a/model_prices_and_context_window.json
+++ b/model_prices_and_context_window.json
@@ -28199,7 +28199,7 @@
         "output_cost_per_token": 1.5e-05,
         "output_cost_per_token_above_200k_tokens": 2.25e-05,
         "source": "https://openrouter.ai/anthropic/claude-sonnet-4.6",
-        "supports_assistant_prefill": true,
+        "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
         "supports_prompt_caching": true,
@@ -28237,7 +28237,7 @@
         "max_tokens": 128000,
         "mode": "chat",
         "output_cost_per_token": 2.5e-05,
-        "supports_assistant_prefill": true,
+        "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
         "supports_prompt_caching": true,
@@ -33493,7 +33493,7 @@
         "max_tokens": 64000,
         "mode": "chat",
         "output_cost_per_token": 2.5e-05,
-        "supports_assistant_prefill": true,
+        "supports_assistant_prefill": false,
         "supports_computer_use": true,
         "supports_function_calling": true,
         "supports_prompt_caching": true,
diff --git a/tests/test_litellm/router_utils/test_fallback_event_handlers.py b/tests/test_litellm/router_utils/test_fallback_event_handlers.py
index 316429cfe0a..d7e5e19edda 100644
--- a/tests/test_litellm/router_utils/test_fallback_event_handlers.py
+++ b/tests/test_litellm/router_utils/test_fallback_event_handlers.py
@@ -65,6 +65,7 @@ def _assert_legacy_prefill(result):
         "anthropic/claude-sonnet-4-6",
         "vertex_ai/claude-sonnet-4-6",
         "claude-opus-4-6",
+        "openrouter/anthropic/claude-sonnet-4.6",  # dot-variant registry key
     ],
 )
 def test_prefill_rejecting_models_get_user_continuation(model):