diff --git a/nanobot/providers/litellm_provider.py b/nanobot/providers/litellm_provider.py
index 7402a2b..0918954 100644
--- a/nanobot/providers/litellm_provider.py
+++ b/nanobot/providers/litellm_provider.py
@@ -12,8 +12,9 @@ from nanobot.providers.base import LLMProvider, LLMResponse, ToolCallRequest
 from nanobot.providers.registry import find_by_model, find_gateway
 
 
-# Standard OpenAI chat-completion message keys; extras (e.g. reasoning_content) are stripped for strict providers.
-_ALLOWED_MSG_KEYS = frozenset({"role", "content", "tool_calls", "tool_call_id", "name"})
+# Standard OpenAI chat-completion message keys plus reasoning_content for
+# thinking-enabled models (Kimi k2.5, DeepSeek-R1, etc.).
+_ALLOWED_MSG_KEYS = frozenset({"role", "content", "tool_calls", "tool_call_id", "name", "reasoning_content"})
 
 
 class LiteLLMProvider(LLMProvider):