diff --git a/pkg/agent/loop.go b/pkg/agent/loop.go
index cc14ceaf0..ec2cfe4e8 100644
--- a/pkg/agent/loop.go
+++ b/pkg/agent/loop.go
@@ -378,8 +378,9 @@ func (al *AgentLoop) runLLMIteration(ctx context.Context, messages []providers.M
 
 		// Build assistant message with tool calls
 		assistantMsg := providers.Message{
-			Role:    "assistant",
-			Content: response.Content,
+			Role:            "assistant",
+			Content:         response.Content,
+			ThinkingContent: response.ThinkingContent,
 		}
 		for _, tc := range response.ToolCalls {
 			argumentsJSON, _ := json.Marshal(tc.Arguments)
diff --git a/pkg/providers/claude_provider.go b/pkg/providers/claude_provider.go
index ae6aca96d..8f89ee5ea 100644
--- a/pkg/providers/claude_provider.go
+++ b/pkg/providers/claude_provider.go
@@ -77,6 +77,14 @@ func buildClaudeParams(messages []Message, tools []ToolDefinition, model string,
 		case "assistant":
 			if len(msg.ToolCalls) > 0 {
 				var blocks []anthropic.ContentBlockParamUnion
+				// Add thinking block if present (required for extended thinking mode)
+				if msg.ThinkingContent != "" {
+					blocks = append(blocks, anthropic.ContentBlockParamUnion{
+						OfThinking: &anthropic.ThinkingBlockParam{
+							Thinking: msg.ThinkingContent,
+						},
+					})
+				}
 				if msg.Content != "" {
 					blocks = append(blocks, anthropic.NewTextBlock(msg.Content))
 				}
@@ -85,9 +93,16 @@ func buildClaudeParams(messages []Message, tools []ToolDefinition, model string,
 				}
 				anthropicMessages = append(anthropicMessages, anthropic.NewAssistantMessage(blocks...))
 			} else {
-				anthropicMessages = append(anthropicMessages,
-					anthropic.NewAssistantMessage(anthropic.NewTextBlock(msg.Content)),
-				)
+				var blocks []anthropic.ContentBlockParamUnion
+				if msg.ThinkingContent != "" {
+					blocks = append(blocks, anthropic.ContentBlockParamUnion{
+						OfThinking: &anthropic.ThinkingBlockParam{
+							Thinking: msg.ThinkingContent,
+						},
+					})
+				}
+				blocks = append(blocks, anthropic.NewTextBlock(msg.Content))
+				anthropicMessages = append(anthropicMessages, anthropic.NewAssistantMessage(blocks...))
 			}
 		case "tool":
 			anthropicMessages = append(anthropicMessages,
@@ -150,10 +165,14 @@ func translateToolsForClaude(tools []ToolDefinition) []anthropic.ToolUnionParam
 
 func parseClaudeResponse(resp *anthropic.Message) *LLMResponse {
 	var content string
+	var thinkingContent string
 	var toolCalls []ToolCall
 
 	for _, block := range resp.Content {
 		switch block.Type {
+		case "thinking":
+			tb := block.AsThinking()
+			thinkingContent += tb.Thinking
 		case "text":
 			tb := block.AsText()
 			content += tb.Text
@@ -182,9 +201,10 @@ func parseClaudeResponse(resp *anthropic.Message) *LLMResponse {
 	}
 
 	return &LLMResponse{
-		Content:      content,
-		ToolCalls:    toolCalls,
-		FinishReason: finishReason,
+		Content:         content,
+		ThinkingContent: thinkingContent,
+		ToolCalls:       toolCalls,
+		FinishReason:    finishReason,
 		Usage: &UsageInfo{
 			PromptTokens:     int(resp.Usage.InputTokens),
 			CompletionTokens: int(resp.Usage.OutputTokens),
diff --git a/pkg/providers/http_provider.go b/pkg/providers/http_provider.go
index 6f188e2f0..1b0b44199 100644
--- a/pkg/providers/http_provider.go
+++ b/pkg/providers/http_provider.go
@@ -60,9 +60,41 @@ func (p *HTTPProvider) Chat(ctx context.Context, messages []Message, tools []Too
 		}
 	}
 
+	// Convert messages to API format, including reasoning_content for thinking models
+	apiMessages := make([]map[string]interface{}, 0, len(messages))
+	for _, msg := range messages {
+		apiMsg := map[string]interface{}{
+			"role":    msg.Role,
+			"content": msg.Content,
+		}
+		// Include reasoning_content for assistant messages with thinking content
+		if msg.Role == "assistant" && msg.ThinkingContent != "" {
+			apiMsg["reasoning_content"] = msg.ThinkingContent
+		}
+		if len(msg.ToolCalls) > 0 {
+			toolCalls := make([]map[string]interface{}, 0, len(msg.ToolCalls))
+			for _, tc := range msg.ToolCalls {
+				argsJSON, _ := json.Marshal(tc.Arguments)
+				toolCalls = append(toolCalls, map[string]interface{}{
+					"id":   tc.ID,
+					"type": "function",
+					"function": map[string]interface{}{
+						"name":      tc.Name,
+						"arguments": string(argsJSON),
+					},
+				})
+			}
+			apiMsg["tool_calls"] = toolCalls
+		}
+		if msg.ToolCallID != "" {
+			apiMsg["tool_call_id"] = msg.ToolCallID
+		}
+		apiMessages = append(apiMessages, apiMsg)
+	}
+
 	requestBody := map[string]interface{}{
 		"model":    model,
-		"messages": messages,
+		"messages": apiMessages,
 	}
 
 	if len(tools) > 0 {
@@ -126,8 +158,9 @@ func (p *HTTPProvider) parseResponse(body []byte) (*LLMResponse, error) {
 	var apiResponse struct {
 		Choices []struct {
 			Message struct {
-				Content   string `json:"content"`
-				ToolCalls []struct {
+				Content          string `json:"content"`
+				ReasoningContent string `json:"reasoning_content"`
+				ToolCalls        []struct {
 					ID       string `json:"id"`
 					Type     string `json:"type"`
 					Function *struct {
@@ -185,10 +218,11 @@ func (p *HTTPProvider) parseResponse(body []byte) (*LLMResponse, error) {
 	}
 
 	return &LLMResponse{
-		Content:      choice.Message.Content,
-		ToolCalls:    toolCalls,
-		FinishReason: choice.FinishReason,
-		Usage:        apiResponse.Usage,
+		Content:         choice.Message.Content,
+		ThinkingContent: choice.Message.ReasoningContent,
+		ToolCalls:       toolCalls,
+		FinishReason:    choice.FinishReason,
+		Usage:           apiResponse.Usage,
 	}, nil
 }
 
diff --git a/pkg/providers/types.go b/pkg/providers/types.go
index 88b62e975..5c7fa2ba9 100644
--- a/pkg/providers/types.go
+++ b/pkg/providers/types.go
@@ -16,10 +16,11 @@ type FunctionCall struct {
 }
 
 type LLMResponse struct {
-	Content      string     `json:"content"`
-	ToolCalls    []ToolCall `json:"tool_calls,omitempty"`
-	FinishReason string     `json:"finish_reason"`
-	Usage        *UsageInfo `json:"usage,omitempty"`
+	Content         string     `json:"content"`
+	ToolCalls       []ToolCall `json:"tool_calls,omitempty"`
+	FinishReason    string     `json:"finish_reason"`
+	Usage           *UsageInfo `json:"usage,omitempty"`
+	ThinkingContent string     `json:"thinking_content,omitempty"` // For Claude extended thinking
 }
 
 type UsageInfo struct {
@@ -29,10 +30,11 @@ type UsageInfo struct {
 }
 
 type Message struct {
-	Role       string     `json:"role"`
-	Content    string     `json:"content"`
-	ToolCalls  []ToolCall `json:"tool_calls,omitempty"`
-	ToolCallID string     `json:"tool_call_id,omitempty"`
+	Role            string     `json:"role"`
+	Content         string     `json:"content"`
+	ToolCalls       []ToolCall `json:"tool_calls,omitempty"`
+	ToolCallID      string     `json:"tool_call_id,omitempty"`
+	ThinkingContent string     `json:"thinking_content,omitempty"` // For Claude extended thinking
 }
 
 type LLMProvider interface {