fix(bedrock_mantle): route xai.grok-4.3 via /openai/v1 frontier path (#33027)

grok-4.3 is a third-party frontier model on Bedrock Mantle, served on the
/openai/v1 base (like gpt-5.x and gemma-4), not the standard /v1 path used by
open-weights models such as gpt-oss. #31916 added the model without
use_openai_responses_path, so mantle_base_segment() routed it to /v1, where
Bedrock rejects the call with "Berm is not enabled for this account"
(access_denied) — the model is only reachable on the frontier /openai/v1 path.

Add use_openai_responses_path=true to the bedrock_mantle/xai.grok-4.3 price-map
entry (both model_prices_and_context_window.json and the backup) so
mantle_base_segment() returns "openai/v1", and update the registry test to
assert use_openai_path is True.

litellm/model_prices_and_context_window_backup.json

@@ -43574,6 +43574,7 @@
         "supports_vision": true
     },
     "bedrock_mantle/xai.grok-4.3": {
+        "use_openai_responses_path": true,
         "input_cost_per_token": 1.25e-06,
         "output_cost_per_token": 2.5e-06,
         "cache_read_input_token_cost": 2e-07,

model_prices_and_context_window.json

@@ -43806,6 +43806,7 @@
         "supports_vision": true
     },
     "bedrock_mantle/xai.grok-4.3": {
+        "use_openai_responses_path": true,
         "input_cost_per_token": 1.25e-06,
         "output_cost_per_token": 2.5e-06,
         "cache_read_input_token_cost": 2e-07,

tests/test_litellm/llms/bedrock_mantle/test_bedrock_mantle_responses_transformation.py

@@ -460,7 +460,12 @@ class TestBedrockMantleResponsesRegistry:
             model="xai.grok-4.3",
         )
         assert isinstance(cfg, BedrockMantleResponsesAPIConfig)
-        assert cfg.use_openai_path is False
+        # grok-4.3 is a third-party frontier model on Bedrock Mantle, served on the
+        # /openai/v1 base (like gpt-5.x / gemma-4), not the standard /v1 path used by
+        # open-weights models such as gpt-oss. The standard /v1 base returns
+        # "Berm is not enabled for this account", so the price-map entry carries
+        # use_openai_responses_path=true.
+        assert cfg.use_openai_path is True
 
     def test_unmapped_frontier_model_falls_through_to_none(self, restore_model_cost):
         # The gate is data-driven, not name-based: an unseen model not yet in the