diff --git a/lib/crewai/src/crewai/agents/agent_adapters/openai_agents/openai_agent_tool_adapter.py b/lib/crewai/src/crewai/agents/agent_adapters/openai_agents/openai_agent_tool_adapter.py
index b6cda1009..7543305f0 100644
--- a/lib/crewai/src/crewai/agents/agent_adapters/openai_agents/openai_agent_tool_adapter.py
+++ b/lib/crewai/src/crewai/agents/agent_adapters/openai_agents/openai_agent_tool_adapter.py
@@ -16,7 +16,7 @@ from crewai.agents.agent_adapters.openai_agents.protocols import (
 )
 from crewai.tools import BaseTool
 from crewai.utilities.import_utils import require
-from crewai.utilities.pydantic_schema_utils import add_key_in_dict_recursively
+from crewai.utilities.pydantic_schema_utils import force_additional_properties_false
 from crewai.utilities.string_utils import sanitize_tool_name
 
 
@@ -136,13 +136,7 @@ class OpenAIAgentToolAdapter(BaseToolAdapter):
         for tool in tools:
             schema: dict[str, Any] = tool.args_schema.model_json_schema()
 
-            schema = add_key_in_dict_recursively(
-                schema,
-                key="additionalProperties",
-                value=False,
-                criteria=lambda d: d.get("type") == "object"
-                and "additionalProperties" not in d,
-            )
+            schema = force_additional_properties_false(schema)
 
             schema.update({"type": "object"})
 
diff --git a/lib/crewai/src/crewai/llms/providers/openai/completion.py b/lib/crewai/src/crewai/llms/providers/openai/completion.py
index 78269f98a..c3c5f6292 100644
--- a/lib/crewai/src/crewai/llms/providers/openai/completion.py
+++ b/lib/crewai/src/crewai/llms/providers/openai/completion.py
@@ -1521,13 +1521,16 @@ class OpenAICompletion(BaseLLM):
     ) -> list[dict[str, Any]]:
         """Convert CrewAI tool format to OpenAI function calling format."""
         from crewai.llms.providers.utils.common import safe_tool_conversion
+        from crewai.utilities.pydantic_schema_utils import (
+            force_additional_properties_false,
+        )
 
         openai_tools = []
 
         for tool in tools:
             name, description, parameters = safe_tool_conversion(tool, "OpenAI")
 
-            openai_tool = {
+            openai_tool: dict[str, Any] = {
                 "type": "function",
                 "function": {
                     "name": name,
@@ -1537,10 +1540,11 @@ class OpenAICompletion(BaseLLM):
             }
 
             if parameters:
-                if isinstance(parameters, dict):
-                    openai_tool["function"]["parameters"] = parameters  # type: ignore
-                else:
-                    openai_tool["function"]["parameters"] = dict(parameters)
+                params_dict = (
+                    parameters if isinstance(parameters, dict) else dict(parameters)
+                )
+                params_dict = force_additional_properties_false(params_dict)
+                openai_tool["function"]["parameters"] = params_dict
 
             openai_tools.append(openai_tool)
         return openai_tools
diff --git a/lib/crewai/src/crewai/utilities/pydantic_schema_utils.py b/lib/crewai/src/crewai/utilities/pydantic_schema_utils.py
index 9e1982e44..2b50caea8 100644
--- a/lib/crewai/src/crewai/utilities/pydantic_schema_utils.py
+++ b/lib/crewai/src/crewai/utilities/pydantic_schema_utils.py
@@ -127,6 +127,36 @@ def add_key_in_dict_recursively(
     return d
 
 
+def force_additional_properties_false(d: Any) -> Any:
+    """Force additionalProperties=false on all object-type dicts recursively.
+
+    OpenAI strict mode requires all objects to have additionalProperties=false.
+    This function overwrites any existing value to ensure compliance.
+
+    Also ensures objects have properties and required arrays, even if empty,
+    as OpenAI strict mode requires these for all object types.
+
+    Args:
+        d: The dictionary/list to modify.
+
+    Returns:
+        The modified dictionary/list.
+    """
+    if isinstance(d, dict):
+        if d.get("type") == "object":
+            d["additionalProperties"] = False
+            if "properties" not in d:
+                d["properties"] = {}
+            if "required" not in d:
+                d["required"] = []
+        for v in d.values():
+            force_additional_properties_false(v)
+    elif isinstance(d, list):
+        for i in d:
+            force_additional_properties_false(i)
+    return d
+
+
 def fix_discriminator_mappings(schema: dict[str, Any]) -> dict[str, Any]:
     """Replace '#/$defs/...' references in discriminator.mapping with just the model name.
 
@@ -278,13 +308,7 @@ def generate_model_description(model: type[BaseModel]) -> dict[str, Any]:
     """
     json_schema = model.model_json_schema(ref_template="#/$defs/{model}")
 
-    json_schema = add_key_in_dict_recursively(
-        json_schema,
-        key="additionalProperties",
-        value=False,
-        criteria=lambda d: d.get("type") == "object"
-        and "additionalProperties" not in d,
-    )
+    json_schema = force_additional_properties_false(json_schema)
 
     json_schema = resolve_refs(json_schema)
 
@@ -378,20 +402,8 @@ def create_model_from_schema(  # type: ignore[no-any-unimported]
     """
     effective_root = root_schema or json_schema
 
-    json_schema = add_key_in_dict_recursively(
-        json_schema,
-        key="additionalProperties",
-        value=False,
-        criteria=lambda d: d.get("type") == "object"
-        and "additionalProperties" not in d,
-    )
-    effective_root = add_key_in_dict_recursively(
-        effective_root,
-        key="additionalProperties",
-        value=False,
-        criteria=lambda d: d.get("type") == "object"
-        and "additionalProperties" not in d,
-    )
+    json_schema = force_additional_properties_false(json_schema)
+    effective_root = force_additional_properties_false(effective_root)
 
     if "allOf" in json_schema:
         json_schema = _merge_all_of_schemas(json_schema["allOf"], effective_root)