diff --git a/litellm/batch_completion/main.py b/litellm/batch_completion/main.py
index 702dd194fda..7ec71dcd4bb 100644
--- a/litellm/batch_completion/main.py
+++ b/litellm/batch_completion/main.py
@@ -1,13 +1,29 @@
+from collections.abc import Mapping
 from concurrent.futures import FIRST_COMPLETED, ThreadPoolExecutor, wait
 from typing import Final
 
 import litellm
 from litellm._logging import print_verbose
-from litellm.utils import get_optional_params
+from litellm.utils import get_model_info, get_optional_params
 
 from ..llms.vllm.completion import handler as vllm_handler
 
 
+def _model_info_for_batch(
+    *,
+    model: str,
+    custom_llm_provider: str | None,
+    kwargs: Mapping[str, object],
+) -> Mapping[str, object] | None:
+    from_kwargs: Final = kwargs.get("model_info")
+    if isinstance(from_kwargs, Mapping):
+        return from_kwargs
+    try:
+        return get_model_info(model=model, custom_llm_provider=custom_llm_provider)
+    except Exception:  # noqa: BLE001  # get_model_info raises Exception for unmapped models
+        return None
+
+
 def batch_completion(
     model: str,
     # Optional OpenAI params: see https://platform.openai.com/docs/api-reference/chat/create
@@ -79,9 +95,13 @@ def batch_completion(
             frequency_penalty=frequency_penalty,
             logit_bias=logit_bias,
             user=user,
-            # params to identify the model
             model=model,
             custom_llm_provider=custom_llm_provider,
+            model_info=_model_info_for_batch(
+                model=model,
+                custom_llm_provider=custom_llm_provider,
+                kwargs=kwargs,
+            ),
         )
         results = vllm_handler.batch_completions(
             model=model,
diff --git a/litellm/litellm_core_utils/thinking_param_translation.py b/litellm/litellm_core_utils/thinking_param_translation.py
index c3a183def1b..9e4beeff231 100644
--- a/litellm/litellm_core_utils/thinking_param_translation.py
+++ b/litellm/litellm_core_utils/thinking_param_translation.py
@@ -88,6 +88,29 @@ def _clamp_effort(value: object, allowed: Sequence[str]) -> str | None:
     return None
 
 
+def _mapping_or_none(value: object) -> Mapping[str, object] | None:
+    if isinstance(value, Mapping):
+        return value
+    return None
+
+
+def _merged_mapping_value(left: Mapping[str, object], right: Mapping[str, object], key: str) -> object:
+    if key not in right:
+        return left[key]
+    if key not in left:
+        return right[key]
+    left_map: Final = _mapping_or_none(left[key])
+    right_map: Final = _mapping_or_none(right[key])
+    if left_map is not None and right_map is not None:
+        return _deep_merge_pair(left_map, right_map)
+    return right[key]
+
+
+def _deep_merge_pair(left: Mapping[str, object], right: Mapping[str, object]) -> Mapping[str, object]:
+    keys: Final = frozenset(left) | frozenset(right)
+    return MappingProxyType({key: _merged_mapping_value(left, right, key) for key in keys})
+
+
 def _map_thinking_to_extra_body(
     *,
     thinking_param: str | None,
@@ -117,6 +140,20 @@ def _map_thinking_to_extra_body(
             return MappingProxyType({})
 
 
+def _map_effort_to_extra_body(
+    *,
+    effort: object,
+    effort_values: Sequence[str],
+    send_via: object,
+) -> Mapping[str, object]:
+    clamped: Final = _clamp_effort(effort, effort_values)
+    if clamped is not None:
+        return MappingProxyType({"reasoning_effort": clamped})
+    if not effort_values and send_via == _SEND_VIA_EXTRA_BODY and isinstance(effort, str):
+        return MappingProxyType({"reasoning_effort": effort})
+    return MappingProxyType({})
+
+
 def translate_thinking_params(
     *,
     model_info: Mapping[str, object] | None,
@@ -143,33 +180,33 @@ def translate_thinking_params(
     if thinking is None and effort is None:
         return state
 
-    existing_extra: Final = dict(state.extra_body)
-    patch: dict[str, object] = {}
     keep_thinking: Final = send_via == _SEND_VIA_PROVIDER_MAPPED
-
-    if thinking is not None and send_via == _SEND_VIA_EXTRA_BODY:
-        patch.update(
-            _map_thinking_to_extra_body(
-                thinking_param=thinking_param,
-                thinking=thinking,
-                thinking_values=thinking_values,
-            )
+    thinking_patch: Final = (
+        _map_thinking_to_extra_body(
+            thinking_param=thinking_param,
+            thinking=thinking,
+            thinking_values=thinking_values,
         )
-
-    if effort is not None:
-        clamped: Final = _clamp_effort(effort, effort_values)
-        if clamped is not None:
-            patch["reasoning_effort"] = clamped
-        elif not effort_values and send_via == _SEND_VIA_EXTRA_BODY and isinstance(effort, str):
-            patch["reasoning_effort"] = effort
-
+        if thinking is not None and send_via == _SEND_VIA_EXTRA_BODY
+        else MappingProxyType({})
+    )
+    effort_patch: Final = (
+        _map_effort_to_extra_body(
+            effort=effort,
+            effort_values=effort_values,
+            send_via=send_via,
+        )
+        if effort is not None
+        else MappingProxyType({})
+    )
+    patch: Final = MappingProxyType({**thinking_patch, **effort_patch})
     if not patch:
         return state
 
     thinking_mapped: Final = any(key in patch for key in ("thinking", "enable_thinking", "chat_template_kwargs"))
     next_thinking: Final = thinking if (keep_thinking or not thinking_mapped) else None
     next_effort: Final = None if "reasoning_effort" in patch else effort
-    merged_extra: Final = MappingProxyType({**existing_extra, **patch})
+    merged_extra: Final = _deep_merge_pair(state.extra_body, patch)
     return ThinkingParamsState(
         thinking=next_thinking,
         reasoning_effort=next_effort,
diff --git a/litellm/utils.py b/litellm/utils.py
index c814d988ab0..c1e348f7887 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -4079,8 +4079,8 @@ def _apply_model_info_thinking_translation(
     passed_params: dict,
     non_default_params: dict,
 ) -> None:
-    prior_thinking: Final = non_default_params.get("thinking", passed_params.get("thinking"))
-    prior_effort: Final = non_default_params.get("reasoning_effort", passed_params.get("reasoning_effort"))
+    prior_thinking: Final = non_default_params.get("thinking")
+    prior_effort: Final = non_default_params.get("reasoning_effort")
     existing_extra_raw: Final = passed_params.get("extra_body")
     existing_extra: Final = existing_extra_raw if isinstance(existing_extra_raw, Mapping) else None
     translated: Final = apply_thinking_param_translation(
diff --git a/tests/test_litellm/litellm_core_utils/test_thinking_param_translation.py b/tests/test_litellm/litellm_core_utils/test_thinking_param_translation.py
index 49ebbff9379..c5c91181278 100644
--- a/tests/test_litellm/litellm_core_utils/test_thinking_param_translation.py
+++ b/tests/test_litellm/litellm_core_utils/test_thinking_param_translation.py
@@ -1,3 +1,4 @@
+import importlib
 from types import MappingProxyType
 
 from litellm.litellm_core_utils.thinking_param_translation import (
@@ -65,6 +66,20 @@ def test_translate_chat_template_kwargs():
     }
 
 
+def test_translate_chat_template_kwargs_preserves_existing_nested_keys():
+    result = apply_thinking_param_translation(
+        model_info=_extra_body_model_info(
+            thinking_param="chat_template_kwargs",
+            thinking_values=[],
+        ),
+        thinking={"type": "enabled"},
+        reasoning_effort=None,
+        existing_extra_body={"chat_template_kwargs": {"reasoning_budget": 512}},
+    )
+    assert result.extra_body["chat_template_kwargs"]["reasoning_budget"] == 512
+    assert result.extra_body["chat_template_kwargs"]["enable_thinking"] is True
+
+
 def test_translate_clamps_effort_aliases():
     result = apply_thinking_param_translation(
         model_info=_extra_body_model_info(reasoning_effort_values=["low", "high", "max"]),
@@ -139,3 +154,48 @@ def test_get_optional_params_openai_drop_without_model_info_drops_params():
     assert "reasoning_effort" not in extra_body
     assert optional_params.get("thinking") is None
     assert optional_params.get("reasoning_effort") is None
+
+
+def test_get_optional_params_does_not_reintroduce_dropped_thinking():
+    optional_params = get_optional_params(
+        model="deepseek-v4-flash",
+        custom_llm_provider="openai",
+        drop_params=True,
+        thinking={"type": "enabled"},
+        additional_drop_params=["thinking"],
+        model_info=_extra_body_model_info(
+            thinking_param="chat_template_kwargs",
+            thinking_values=[],
+        ),
+    )
+    extra_body = optional_params.get("extra_body") or {}
+    assert optional_params.get("thinking") is None
+    assert "enable_thinking" not in extra_body
+    assert "chat_template_kwargs" not in extra_body
+
+
+def test_batch_completion_vllm_passes_model_info(monkeypatch):
+    batch_completion_mod = importlib.import_module("litellm.batch_completion.main")
+
+    captured: dict[str, object] = {}
+    looked_up: dict[str, object] = _extra_body_model_info(thinking_param="enable_thinking")
+
+    def fake_get_optional_params(**kwargs: object) -> dict[str, object]:
+        captured.update(kwargs)
+        return {}
+
+    def fake_batch_completions(**kwargs: object) -> list[str]:
+        return ["ok"]
+
+    def fake_get_model_info(**kwargs: object) -> dict[str, object]:
+        return looked_up
+
+    monkeypatch.setattr(batch_completion_mod, "get_optional_params", fake_get_optional_params)
+    monkeypatch.setattr(batch_completion_mod.vllm_handler, "batch_completions", fake_batch_completions)
+    monkeypatch.setattr(batch_completion_mod, "get_model_info", fake_get_model_info)
+
+    batch_completion_mod.batch_completion(
+        model="vllm/some-model",
+        messages=[[{"role": "user", "content": "hi"}]],
+    )
+    assert captured.get("model_info") == looked_up