diff --git a/litellm/llms/ollama/chat/transformation.py b/litellm/llms/ollama/chat/transformation.py
index cb3080e6534..e63448fc0d6 100644
--- a/litellm/llms/ollama/chat/transformation.py
+++ b/litellm/llms/ollama/chat/transformation.py
@@ -28,7 +28,7 @@ from litellm.types.llms.openai import (
 )
 from litellm.types.utils import ModelResponse, ModelResponseStream
 
-from ..common_utils import OllamaError
+from ..common_utils import OllamaError, think_from_reasoning_effort
 
 if TYPE_CHECKING:
     from litellm.litellm_core_utils.litellm_logging import Logging as _LiteLLMLoggingObj
@@ -170,11 +170,17 @@ class OllamaChatConfig(BaseConfig):
             if param == "response_format" and isinstance(value, dict) and value.get("type") == "json_schema":
                 if value.get("json_schema") and value["json_schema"].get("schema"):
                     optional_params["format"] = value["json_schema"]["schema"]
-            if param == "reasoning_effort" and value is not None:
-                if model.startswith("gpt-oss"):
-                    optional_params["think"] = value
-                else:
-                    optional_params["think"] = value in {"low", "medium", "high"}
+            if (
+                param == "reasoning_effort"
+                and (
+                    think := think_from_reasoning_effort(
+                        model,
+                        cast(object, value),  # cast-ok: [LIT006] untyped dict value, widened to object for the helper
+                    )
+                )
+                is not None
+            ):
+                optional_params["think"] = think
             ### FUNCTION CALLING LOGIC ###
             # Ollama 0.4+ supports native tool calling - pass tools directly
             # and let Ollama handle model capability detection
diff --git a/litellm/llms/ollama/common_utils.py b/litellm/llms/ollama/common_utils.py
index 9f46cbc5cd5..96f28b1ed53 100644
--- a/litellm/llms/ollama/common_utils.py
+++ b/litellm/llms/ollama/common_utils.py
@@ -1,5 +1,6 @@
 import base64
 import io
+from collections.abc import Mapping
 from typing import Any, Final
 
 import httpx
@@ -8,6 +9,15 @@ from litellm import verbose_logger
 from litellm.llms.base_llm.chat.transformation import BaseLLMException
 
 
+def think_from_reasoning_effort(model: str, reasoning_effort: object) -> str | bool | None:
+    effort: Final = reasoning_effort.get("effort") if isinstance(reasoning_effort, Mapping) else reasoning_effort
+    if not isinstance(effort, str):
+        return None
+    if model.startswith("gpt-oss"):
+        return effort
+    return effort in {"low", "medium", "high"}
+
+
 class OllamaError(BaseLLMException):
     def __init__(self, status_code: int, message: str, headers: dict | httpx.Headers):
         super().__init__(status_code=status_code, message=message, headers=headers)
diff --git a/litellm/llms/ollama/completion/transformation.py b/litellm/llms/ollama/completion/transformation.py
index b1f69220de7..b712bb7cc5b 100644
--- a/litellm/llms/ollama/completion/transformation.py
+++ b/litellm/llms/ollama/completion/transformation.py
@@ -1,7 +1,7 @@
 import json
 import time
 from collections.abc import AsyncIterator, Iterator
-from typing import TYPE_CHECKING, Any, Final
+from typing import TYPE_CHECKING, Any, Final, cast
 
 from httpx._models import Headers, Response
 from pydantic import BaseModel, ConfigDict, ValidationError
@@ -33,7 +33,7 @@ from litellm.types.utils import (
     StreamingChoices,
 )
 
-from ..common_utils import OllamaError, OllamaModelInfo, _convert_image
+from ..common_utils import OllamaError, OllamaModelInfo, _convert_image, think_from_reasoning_effort
 
 if TYPE_CHECKING:
     from litellm.litellm_core_utils.litellm_logging import Logging as _LiteLLMLoggingObj
@@ -214,11 +214,17 @@ class OllamaConfig(BaseConfig):
                 optional_params["frequency_penalty"] = value
             elif param == "stop":
                 optional_params["stop"] = value
-            elif param == "reasoning_effort" and value is not None:
-                if model.startswith("gpt-oss"):
-                    optional_params["think"] = value
-                else:
-                    optional_params["think"] = value in {"low", "medium", "high"}
+            elif (
+                param == "reasoning_effort"
+                and (
+                    think := think_from_reasoning_effort(
+                        model,
+                        cast(object, value),  # cast-ok: [LIT006] untyped dict value, widened to object for the helper
+                    )
+                )
+                is not None
+            ):
+                optional_params["think"] = think
             elif param == "response_format" and isinstance(value, dict):
                 if value["type"] == "json_object":
                     optional_params["format"] = "json"
diff --git a/tests/unit/llms/ollama/test_ollama_chat_transformation.py b/tests/unit/llms/ollama/test_ollama_chat_transformation.py
index c7fba21d222..d1a9fe6aaa8 100644
--- a/tests/unit/llms/ollama/test_ollama_chat_transformation.py
+++ b/tests/unit/llms/ollama/test_ollama_chat_transformation.py
@@ -1,7 +1,9 @@
 import inspect
 import os
 import sys
-from typing import cast
+from collections.abc import Mapping
+from types import MappingProxyType
+from typing import Final, cast
 
 import pytest
 from pydantic import BaseModel
@@ -989,3 +991,44 @@ class TestOllamaStreamingUsage:
         )
 
         assert result.usage is None
+
+
+class TestOllamaChatReasoningEffort:
+    @pytest.mark.parametrize(
+        "reasoning_effort, expected_think",
+        [
+            ("low", True),
+            ("high", True),
+            ("none", False),
+            ({"effort": "medium"}, True),
+            ({"effort": "medium", "summary": "auto"}, True),
+            (MappingProxyType({"effort": "medium", "summary": "auto"}), True),
+            ({"effort": "none", "summary": "detailed"}, False),
+        ],
+    )
+    def test_reasoning_effort_string_or_dict_maps_to_think(
+        self, reasoning_effort: str | Mapping[str, str], expected_think: bool
+    ) -> None:
+        optional_params: Final = get_optional_params(
+            model="ollama_chat/qwen3:8b",
+            custom_llm_provider="ollama_chat",
+            reasoning_effort=reasoning_effort,
+        )
+        assert optional_params["think"] is expected_think
+
+    def test_reasoning_dict_without_effort_sets_nothing(self) -> None:
+        optional_params: Final = get_optional_params(
+            model="ollama_chat/qwen3:8b",
+            custom_llm_provider="ollama_chat",
+            reasoning_effort={"summary": "auto"},
+        )
+        assert "think" not in optional_params
+
+    def test_reasoning_dict_gpt_oss_forwards_effort_string(self) -> None:
+        optional_params: Final = OllamaChatConfig().map_openai_params(
+            non_default_params={"reasoning_effort": {"effort": "high", "summary": "auto"}},
+            optional_params={},
+            model="gpt-oss:20b",
+            drop_params=False,
+        )
+        assert optional_params["think"] == "high"
diff --git a/tests/unit/llms/ollama/test_ollama_completion_transformation.py b/tests/unit/llms/ollama/test_ollama_completion_transformation.py
index d6215a742f0..531cd190e3d 100644
--- a/tests/unit/llms/ollama/test_ollama_completion_transformation.py
+++ b/tests/unit/llms/ollama/test_ollama_completion_transformation.py
@@ -2,6 +2,9 @@ import base64
 import io
 import json
 import sys
+from collections.abc import Mapping
+from types import MappingProxyType
+from typing import Final
 from litellm._uuid import uuid
 from unittest.mock import MagicMock, patch
 
@@ -775,3 +778,43 @@ def test_transform_request_leaves_unreadable_images_untouched(payload: str) -> N
     data = _transform_image_request(payload, "png")
 
     assert data["images"] == [payload]
+
+
+class TestOllamaConfigReasoningEffort:
+    @pytest.mark.parametrize(
+        "reasoning_effort, expected_think",
+        [
+            ("medium", True),
+            ({"effort": "medium", "summary": "auto"}, True),
+            (MappingProxyType({"effort": "medium", "summary": "auto"}), True),
+            ({"effort": "none"}, False),
+        ],
+    )
+    def test_reasoning_effort_string_or_dict_maps_to_think(
+        self, reasoning_effort: str | Mapping[str, str], expected_think: bool
+    ) -> None:
+        optional_params: Final = OllamaConfig().map_openai_params(
+            non_default_params={"reasoning_effort": reasoning_effort},
+            optional_params={},
+            model="qwen3:8b",
+            drop_params=False,
+        )
+        assert optional_params["think"] is expected_think
+
+    def test_reasoning_dict_gpt_oss_forwards_effort_string(self) -> None:
+        optional_params: Final = OllamaConfig().map_openai_params(
+            non_default_params={"reasoning_effort": {"effort": "high", "summary": "auto"}},
+            optional_params={},
+            model="gpt-oss:20b",
+            drop_params=False,
+        )
+        assert optional_params["think"] == "high"
+
+    def test_reasoning_dict_without_effort_sets_nothing(self) -> None:
+        optional_params: Final = OllamaConfig().map_openai_params(
+            non_default_params={"reasoning_effort": {"summary": "auto"}},
+            optional_params={},
+            model="qwen3:8b",
+            drop_params=False,
+        )
+        assert "think" not in optional_params