feat: reasoning_content in API for reasoning models (#6322)

Signed-off-by: Abhijay007 <Abhijay007j@gmail.com>

crates/goose-server/src/openapi.rs

@@ -21,8 +21,9 @@ use goose::config::declarative_providers::{
 };
 use goose::conversation::message::{
     ActionRequired, ActionRequiredData, FrontendToolRequest, Message, MessageContent,
-    MessageMetadata, RedactedThinkingContent, SystemNotificationContent, SystemNotificationType,
-    ThinkingContent, TokenState, ToolConfirmationRequest, ToolRequest, ToolResponse,
+    MessageMetadata, ReasoningContent, RedactedThinkingContent, SystemNotificationContent,
+    SystemNotificationType, ThinkingContent, TokenState, ToolConfirmationRequest, ToolRequest,
+    ToolResponse,
 };
 
 use crate::routes::recipe_utils::RecipeManifest;
@@ -480,6 +481,7 @@ derive_utoipa!(Icon as IconSchema);
         ActionRequiredData,
         ThinkingContent,
         RedactedThinkingContent,
+        ReasoningContent,
         FrontendToolRequest,
         ResourceContentsSchema,
         SystemNotificationType,

crates/goose/src/context_mgmt/mod.rs

@@ -336,19 +336,19 @@ fn format_message_for_compacting(msg: &Message) -> String {
     let content_parts: Vec<String> = msg
         .content
         .iter()
-        .map(|content| match content {
-            MessageContent::Text(text) => text.text.clone(),
-            MessageContent::Image(img) => format!("[image: {}]", img.mime_type),
+        .filter_map(|content| match content {
+            MessageContent::Text(text) => Some(text.text.clone()),
+            MessageContent::Image(img) => Some(format!("[image: {}]", img.mime_type)),
             MessageContent::ToolRequest(req) => {
                 if let Ok(call) = &req.tool_call {
-                    format!(
+                    Some(format!(
                         "tool_request({}): {}",
                         call.name,
                         serde_json::to_string(&call.arguments)
                             .unwrap_or_else(|_| "<<invalid json>>".to_string())
-                    )
+                    ))
                 } else {
-                    "tool_request: [error]".to_string()
+                    Some("tool_request: [error]".to_string())
                 }
             }
             MessageContent::ToolResponse(res) => {
@@ -362,40 +362,41 @@ fn format_message_for_compacting(msg: &Message) -> String {
                         .collect();
 
                     if !text_items.is_empty() {
-                        format!("tool_response: {}", text_items.join("\n"))
+                        Some(format!("tool_response: {}", text_items.join("\n")))
                     } else {
-                        "tool_response: [non-text content]".to_string()
+                        Some("tool_response: [non-text content]".to_string())
                     }
                 } else {
-                    "tool_response: [error]".to_string()
+                    Some("tool_response: [error]".to_string())
                 }
             }
             MessageContent::ToolConfirmationRequest(req) => {
-                format!("tool_confirmation_request: {}", req.tool_name)
+                Some(format!("tool_confirmation_request: {}", req.tool_name))
             }
             MessageContent::ActionRequired(action) => match &action.data {
                 ActionRequiredData::ToolConfirmation { tool_name, .. } => {
-                    format!("action_required(tool_confirmation): {}", tool_name)
+                    Some(format!("action_required(tool_confirmation): {}", tool_name))
                 }
                 ActionRequiredData::Elicitation { message, .. } => {
-                    format!("action_required(elicitation): {}", message)
+                    Some(format!("action_required(elicitation): {}", message))
                 }
                 ActionRequiredData::ElicitationResponse { id, .. } => {
-                    format!("action_required(elicitation_response): {}", id)
+                    Some(format!("action_required(elicitation_response): {}", id))
                 }
             },
             MessageContent::FrontendToolRequest(req) => {
                 if let Ok(call) = &req.tool_call {
-                    format!("frontend_tool_request: {}", call.name)
+                    Some(format!("frontend_tool_request: {}", call.name))
                 } else {
-                    "frontend_tool_request: [error]".to_string()
+                    Some("frontend_tool_request: [error]".to_string())
                 }
             }
-            MessageContent::Thinking(_) => "thinking".to_string(),
-            MessageContent::RedactedThinking(_) => "redacted_thinking".to_string(),
+            MessageContent::Thinking(_) => None,
+            MessageContent::RedactedThinking(_) => None,
             MessageContent::SystemNotification(notification) => {
-                format!("system_notification: {}", notification.msg)
+                Some(format!("system_notification: {}", notification.msg))
             }
+            MessageContent::Reasoning(_) => None,
         })
         .collect();
 

crates/goose/src/conversation/message.rs

@@ -175,6 +175,11 @@ pub struct SystemNotificationContent {
     pub data: Option<serde_json::Value>,
 }
 
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, ToSchema)]
+pub struct ReasoningContent {
+    pub text: String,
+}
+
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, ToSchema)]
 /// Content passed inside a message, which can be both simple content and tool content
 #[serde(tag = "type", rename_all = "camelCase")]
@@ -189,6 +194,7 @@ pub enum MessageContent {
     Thinking(ThinkingContent),
     RedactedThinking(RedactedThinkingContent),
     SystemNotification(SystemNotificationContent),
+    Reasoning(ReasoningContent),
 }
 
 impl fmt::Display for MessageContent {
@@ -230,6 +236,7 @@ impl fmt::Display for MessageContent {
             MessageContent::SystemNotification(r) => {
                 write!(f, "[SystemNotification: {}]", r.msg)
             }
+            MessageContent::Reasoning(r) => write!(f, "[Reasoning: {}]", r.text),
         }
     }
 }
@@ -443,6 +450,10 @@ impl MessageContent {
         })
     }
 
+    pub fn reasoning<S: Into<String>>(text: S) -> Self {
+        MessageContent::Reasoning(ReasoningContent { text: text.into() })
+    }
+
     pub fn as_system_notification(&self) -> Option<&SystemNotificationContent> {
         if let MessageContent::SystemNotification(ref notification) = self {
             Some(notification)
@@ -514,6 +525,14 @@ impl MessageContent {
             _ => None,
         }
     }
+
+    /// Get the reasoning content if this is a ReasoningContent variant
+    pub fn as_reasoning(&self) -> Option<&ReasoningContent> {
+        match self {
+            MessageContent::Reasoning(reasoning) => Some(reasoning),
+            _ => None,
+        }
+    }
 }
 
 impl From<Content> for MessageContent {

crates/goose/src/providers/formats/anthropic.rs

@@ -124,6 +124,10 @@ pub fn format_messages(messages: &[Message]) -> Vec<Value> {
                         }));
                     }
                 }
+                MessageContent::Reasoning(_reasoning) => {
+                    // Reasoning content is for OpenAI-compatible APIs (e.g., DeepSeek)
+                    // Anthropic doesn't use this format, so skip it
+                }
             }
         }
 

crates/goose/src/providers/formats/bedrock.rs

@@ -113,6 +113,11 @@ pub fn to_bedrock_message_content(content: &MessageContent) -> Result<bedrock::C
                     .build()?,
             )
         }
+        MessageContent::Reasoning(_reasoning) => {
+            // Reasoning content is for OpenAI-compatible APIs (e.g., DeepSeek)
+            // Bedrock doesn't use this format, so skip
+            bedrock::ContentBlock::Text("".to_string())
+        }
     })
 }
 

crates/goose/src/providers/formats/databricks.rs

@@ -205,6 +205,10 @@ fn format_messages(messages: &[Message], image_format: &ImageFormat) -> Vec<Data
                 MessageContent::SystemNotification(_)
                 | MessageContent::ToolConfirmationRequest(_)
                 | MessageContent::ActionRequired(_) => {}
+                MessageContent::Reasoning(_reasoning) => {
+                    // Reasoning content is for OpenAI-compatible APIs (e.g., DeepSeek)
+                    // Databricks doesn't use this format, so skip
+                }
             }
         }
 

crates/goose/src/providers/formats/openai.rs

@@ -52,6 +52,7 @@ struct Delta {
     role: Option<String>,
     tool_calls: Option<Vec<DeltaToolCall>>,
     reasoning_details: Option<Vec<Value>>,
+    reasoning_content: Option<String>,
 }
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -80,6 +81,7 @@ pub fn format_messages(messages: &[Message], image_format: &ImageFormat) -> Vec<
         let mut output = Vec::new();
         let mut content_array = Vec::new();
         let mut text_array = Vec::new();
+        let mut reasoning_text: Option<String> = None;
 
         for content in &message.content {
             match content {
@@ -112,6 +114,9 @@ pub fn format_messages(messages: &[Message], image_format: &ImageFormat) -> Vec<
                 MessageContent::SystemNotification(_) => {
                     continue;
                 }
+                MessageContent::Reasoning(r) => {
+                    reasoning_text = Some(r.text.clone());
+                }
                 MessageContent::ToolRequest(request) => match &request.tool_call {
                     Ok(tool_call) => {
                         let sanitized_name = sanitize_function_name(&tool_call.name);
@@ -277,6 +282,17 @@ pub fn format_messages(messages: &[Message], image_format: &ImageFormat) -> Vec<
             converted["content"] = json!(null);
         }
 
+        // DeepSeek requires reasoning_content field when tool_calls are present
+        // Set it to the captured reasoning text, or empty string if not present
+        if converted.get("tool_calls").is_some() {
+            let reasoning = reasoning_text.unwrap_or_default();
+            converted["reasoning_content"] = json!(reasoning);
+        } else if let Some(reasoning) = reasoning_text {
+            if !reasoning.is_empty() {
+                converted["reasoning_content"] = json!(reasoning);
+            }
+        }
+
         if converted.get("content").is_some() || converted.get("tool_calls").is_some() {
             output.insert(0, converted);
         }
@@ -330,6 +346,15 @@ pub fn response_to_message(response: &Value) -> anyhow::Result<Message> {
 
     let mut content = Vec::new();
 
+    // Capture reasoning_content if present (for DeepSeek reasoning models)
+    if let Some(reasoning_content) = original.get("reasoning_content") {
+        if let Some(reasoning_str) = reasoning_content.as_str() {
+            if !reasoning_str.is_empty() {
+                content.push(MessageContent::reasoning(reasoning_str));
+            }
+        }
+    }
+
     if let Some(text) = original.get("content") {
         if let Some(text_str) = text.as_str() {
             content.push(MessageContent::text(text_str));
@@ -678,23 +703,44 @@ where
                     Some(msg),
                     usage,
                 )
-            } else if chunk.choices[0].delta.content.is_some() {
-                let text = chunk.choices[0].delta.content.as_ref().unwrap();
-                let mut msg = Message::new(
-                    Role::Assistant,
-                    chrono::Utc::now().timestamp(),
-                    vec![MessageContent::text(text)],
-                );
+            } else if chunk.choices[0].delta.content.is_some() || chunk.choices[0].delta.reasoning_content.is_some() {
+                let mut content = Vec::new();
 
-                // Add ID if present
-                if let Some(id) = chunk.id {
-                    msg = msg.with_id(id);
+                if let Some(reasoning) = &chunk.choices[0].delta.reasoning_content {
+                    if !reasoning.is_empty() {
+                        content.push(MessageContent::reasoning(reasoning));
+                    }
                 }
 
-                yield (
-                    Some(msg),
-                    usage,
-                )
+                if let Some(text) = &chunk.choices[0].delta.content {
+                    if !text.is_empty() {
+                        content.push(MessageContent::text(text));
+                    }
+                }
+
+                if !content.is_empty() {
+                    let mut msg = Message::new(
+                        Role::Assistant,
+                        chrono::Utc::now().timestamp(),
+                        content,
+                    );
+
+                    // Add ID if present
+                    if let Some(id) = chunk.id {
+                        msg = msg.with_id(id);
+                    }
+
+                    yield (
+                        Some(msg),
+                        if chunk.choices[0].finish_reason.is_some() {
+                            usage
+                        } else {
+                            None
+                        },
+                    )
+                } else if usage.is_some() {
+                    yield (None, usage)
+                }
             } else if usage.is_some() {
                 yield (None, usage)
             }
@@ -1834,4 +1880,82 @@ data: [DONE]"#;
 
         panic!("Expected tool call message with nested extra_content metadata");
     }
+
+    #[test]
+    fn test_response_to_message_with_reasoning_content() -> anyhow::Result<()> {
+        // Test capturing reasoning_content from DeepSeek reasoning models
+        let response = json!({
+            "choices": [{
+                "role": "assistant",
+                "message": {
+                    "reasoning_content": "Let me think about this step by step...",
+                    "content": "The answer is 9.11 is greater than 9.8"
+                }
+            }],
+            "usage": {
+                "input_tokens": 10,
+                "output_tokens": 25,
+                "total_tokens": 35
+            }
+        });
+
+        let message = response_to_message(&response)?;
+        assert_eq!(message.content.len(), 2);
+
+        // First should be reasoning content
+        if let MessageContent::Reasoning(reasoning) = &message.content[0] {
+            assert_eq!(reasoning.text, "Let me think about this step by step...");
+        } else {
+            panic!("Expected Reasoning content");
+        }
+
+        // Second should be text content
+        if let MessageContent::Text(text) = &message.content[1] {
+            assert_eq!(text.text, "The answer is 9.11 is greater than 9.8");
+        } else {
+            panic!("Expected Text content");
+        }
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_format_messages_with_reasoning_content() -> anyhow::Result<()> {
+        // Test that reasoning_content is properly included in formatted messages
+        let mut message = Message::assistant()
+            .with_content(MessageContent::reasoning("Thinking through the problem..."))
+            .with_text("The result is 42");
+
+        // Add a tool call to test that reasoning_content works with tool calls
+        message = message.with_tool_request(
+            "tool1",
+            Ok(rmcp::model::CallToolRequestParams {
+                meta: None,
+                task: None,
+                name: "test_tool".into(),
+                arguments: Some(rmcp::object!({"param": "value"})),
+            }),
+        );
+
+        let spec = format_messages(&[message], &ImageFormat::OpenAi);
+
+        assert_eq!(spec.len(), 1);
+        assert_eq!(spec[0]["role"], "assistant");
+
+        // Should have reasoning_content field
+        assert!(spec[0].get("reasoning_content").is_some());
+        assert_eq!(
+            spec[0]["reasoning_content"],
+            "Thinking through the problem..."
+        );
+
+        // Should have content
+        assert_eq!(spec[0]["content"], "The result is 42");
+
+        // Should have tool_calls
+        assert!(spec[0]["tool_calls"].is_array());
+        assert_eq!(spec[0]["tool_calls"][0]["function"]["name"], "test_tool");
+
+        Ok(())
+    }
 }

crates/goose/src/providers/formats/snowflake.rs

@@ -65,6 +65,10 @@ pub fn format_messages(messages: &[Message]) -> Vec<Value> {
                 MessageContent::FrontendToolRequest(_tool_request) => {
                     // Skip frontend tool requests
                 }
+                MessageContent::Reasoning(_reasoning) => {
+                    // Reasoning content is for OpenAI-compatible APIs (e.g., DeepSeek)
+                    // Snowflake doesn't use this format, so skip
+                }
             }
         }
 

ui/desktop/openapi.json

@@ -5042,6 +5042,27 @@
                 }
               }
             ]
+          },
+          {
+            "allOf": [
+              {
+                "$ref": "#/components/schemas/ReasoningContent"
+              },
+              {
+                "type": "object",
+                "required": [
+                  "type"
+                ],
+                "properties": {
+                  "type": {
+                    "type": "string",
+                    "enum": [
+                      "reasoning"
+                    ]
+                  }
+                }
+              }
+            ]
           }
         ],
         "description": "Content passed inside a message, which can be both simple content and tool content",
@@ -5724,6 +5745,17 @@
           }
         }
       },
+      "ReasoningContent": {
+        "type": "object",
+        "required": [
+          "text"
+        ],
+        "properties": {
+          "text": {
+            "type": "string"
+          }
+        }
+      },
       "Recipe": {
         "type": "object",
         "required": [

ui/desktop/src/api/types.gen.ts

@@ -564,6 +564,8 @@ export type MessageContent = (TextContent & {
     type: 'redactedThinking';
 }) | (SystemNotificationContent & {
     type: 'systemNotification';
+}) | (ReasoningContent & {
+    type: 'reasoning';
 });
 
 export type MessageEvent = {
@@ -833,6 +835,10 @@ export type ReadResourceResponse = {
     uri: string;
 };
 
+export type ReasoningContent = {
+    text: string;
+};
+
 export type Recipe = {
     activities?: Array<string> | null;
     author?: Author | null;

ui/desktop/src/components/GooseMessage.tsx

@@ -5,6 +5,7 @@ import MarkdownContent from './MarkdownContent';
 import ToolCallWithResponse from './ToolCallWithResponse';
 import {
   getTextAndImageContent,
+  getReasoningContent,
   getToolRequests,
   getToolResponses,
   getToolConfirmationContent,
@@ -47,6 +48,7 @@ export default function GooseMessage({
   const contentRef = useRef<HTMLDivElement | null>(null);
 
   let { textContent, imagePaths } = getTextAndImageContent(message);
+  const reasoningContent = getReasoningContent(message);
 
   const splitChainOfThought = (text: string): { displayText: string; cotText: string | null } => {
     const regex = /<think>([\s\S]*?)<\/think>/i;
@@ -129,6 +131,17 @@ export default function GooseMessage({
   return (
     <div className="goose-message flex w-[90%] justify-start min-w-0">
       <div className="flex flex-col w-full min-w-0">
+        {reasoningContent && (
+          <details className="mb-2">
+            <summary className="cursor-pointer text-xs text-textSubtle select-none">
+              Show reasoning
+            </summary>
+            <div className="mt-2 text-sm">
+              <MarkdownContent content={reasoningContent} />
+            </div>
+          </details>
+        )}
+
         {cotText && (
           <details className="bg-background-muted border border-border-default rounded p-2 mb-2">
             <summary className="cursor-pointer text-sm text-text-muted select-none">

ui/desktop/src/components/sessions/SessionViewComponents.tsx

@@ -8,6 +8,7 @@ import ToolCallWithResponse from '../ToolCallWithResponse';
 import ImagePreview from '../ImagePreview';
 import {
   getTextAndImageContent,
+  getReasoningContent,
   ToolRequestMessageContent,
   ToolResponseMessageContent,
 } from '../../types/message';
@@ -82,6 +83,7 @@ export const SessionMessages: React.FC<SessionMessagesProps> = ({
               messages
                 .map((message, index) => {
                   const { textContent, imagePaths } = getTextAndImageContent(message);
+                  const reasoningContent = getReasoningContent(message);
 
                   // Get tool requests from the message
                   const toolRequests = message.content
@@ -119,6 +121,19 @@ export const SessionMessages: React.FC<SessionMessagesProps> = ({
                       </div>
 
                       <div className="flex flex-col w-full">
+                        {/* Reasoning content */}
+                        {reasoningContent && (
+                          <details className="mb-2">
+                            <summary className="cursor-pointer text-xs text-textSubtle select-none">
+                              Show reasoning
+                            </summary>
+                            <div className="mt-2 text-sm">
+                              <MarkdownContent content={reasoningContent} />
+                            </div>
+                          </details>
+                        )}
+
+                        {/* Text content */}
                         {textContent && (
                           <div
                             className={`${toolRequests.length > 0 || imagePaths.length > 0 ? 'mb-4' : ''}`}

ui/desktop/src/types/message.ts

@@ -97,6 +97,18 @@ export function getTextAndImageContent(message: Message): {
   return { textContent, imagePaths };
 }
 
+export function getReasoningContent(message: Message): string | null {
+  const reasoningContents = message.content
+    .filter((content) => content.type === 'reasoning')
+    .map((content) => {
+      if ('text' in content) return content.text;
+      return '';
+    })
+    .filter((text) => text.length > 0);
+
+  return reasoningContents.length > 0 ? reasoningContents.join('') : null;
+}
+
 export function getToolRequests(message: Message): (ToolRequest & { type: 'toolRequest' })[] {
   return message.content.filter(
     (content): content is ToolRequest & { type: 'toolRequest' } => content.type === 'toolRequest'