diff --git a/src/models/mod.rs b/src/models/mod.rs
index a56fa8da..0a3f8671 100644
--- a/src/models/mod.rs
+++ b/src/models/mod.rs
@@ -38,7 +38,7 @@ pub struct ChatMessage {
     pub role: String, // "system", "user", "assistant", "tool"
     #[serde(flatten)]
     pub content: MessageContent,
-    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(alias = "reasoning", alias = "thought", skip_serializing_if = "Option::is_none")]
     pub reasoning_content: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub tool_calls: Option<Vec<ToolCall>>,
@@ -192,7 +192,7 @@ pub struct ChatStreamChoice {
 pub struct ChatStreamDelta {
     pub role: Option<String>,
     pub content: Option<String>,
-    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(alias = "reasoning", alias = "thought", skip_serializing_if = "Option::is_none")]
     pub reasoning_content: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub tool_calls: Option<Vec<ToolCallDelta>>,
diff --git a/src/providers/deepseek.rs b/src/providers/deepseek.rs
index c964ee55..207f3f53 100644
--- a/src/providers/deepseek.rs
+++ b/src/providers/deepseek.rs
@@ -58,7 +58,34 @@ impl super::Provider for DeepSeekProvider {
 
     async fn chat_completion(&self, request: UnifiedRequest) -> Result<ProviderResponse, AppError> {
         let messages_json = helpers::messages_to_openai_json(&request.messages).await?;
-        let body = helpers::build_openai_body(&request, messages_json, false);
+        let mut body = helpers::build_openai_body(&request, messages_json, false);
+
+        // Sanitize and fix for deepseek-reasoner (R1)
+        if request.model == "deepseek-reasoner" {
+            if let Some(obj) = body.as_object_mut() {
+                // Remove unsupported parameters
+                obj.remove("temperature");
+                obj.remove("top_p");
+                obj.remove("presence_penalty");
+                obj.remove("frequency_penalty");
+                obj.remove("logit_bias");
+                obj.remove("logprobs");
+                obj.remove("top_logprobs");
+
+                // ENSURE: assistant messages with tool_calls must have reasoning_content
+                if let Some(messages) = obj.get_mut("messages").and_then(|m| m.as_array_mut()) {
+                    for m in messages {
+                        if m["role"] == "assistant" && m.get("tool_calls").is_some() {
+                            if m.get("reasoning_content").is_none() || m["reasoning_content"].is_null() {
+                                // DeepSeek R1 requires reasoning_content for tool calls in history.
+                                // If missing (e.g. from client or other model), inject a placeholder.
+                                m["reasoning_content"] = serde_json::json!("Thinking...");
+                            }
+                        }
+                    }
+                }
+            }
+        }
 
         let response = self
             .client
@@ -118,9 +145,34 @@ impl super::Provider for DeepSeekProvider {
         let messages_json = helpers::messages_to_openai_json_text_only(&request.messages).await?;
         let mut body = helpers::build_openai_body(&request, messages_json, true);
 
-        // Standard OpenAI cleanup
-        if let Some(obj) = body.as_object_mut() {
-            obj.remove("stream_options");
+        // Sanitize and fix for deepseek-reasoner (R1)
+        if request.model == "deepseek-reasoner" {
+            if let Some(obj) = body.as_object_mut() {
+                obj.remove("stream_options");
+                obj.remove("temperature");
+                obj.remove("top_p");
+                obj.remove("presence_penalty");
+                obj.remove("frequency_penalty");
+                obj.remove("logit_bias");
+                obj.remove("logprobs");
+                obj.remove("top_logprobs");
+
+                // ENSURE: assistant messages with tool_calls must have reasoning_content
+                if let Some(messages) = obj.get_mut("messages").and_then(|m| m.as_array_mut()) {
+                    for m in messages {
+                        if m["role"] == "assistant" && m.get("tool_calls").is_some() {
+                            if m.get("reasoning_content").is_none() || m["reasoning_content"].is_null() {
+                                m["reasoning_content"] = serde_json::json!("Thinking...");
+                            }
+                        }
+                    }
+                }
+            }
+        } else {
+            // For standard deepseek-chat, keep it clean
+            if let Some(obj) = body.as_object_mut() {
+                obj.remove("stream_options");
+            }
         }
 
         let url = format!("{}/chat/completions", self.config.base_url);