diff --git a/core/src/types/thread/threadEntity.ts b/core/src/types/thread/threadEntity.ts
index dd88b10ec..ab61787e6 100644
--- a/core/src/types/thread/threadEntity.ts
+++ b/core/src/types/thread/threadEntity.ts
@@ -27,8 +27,8 @@ export type Thread = {
  * @stored
  */
 export type ThreadAssistantInfo = {
-  assistant_id: string
-  assistant_name: string
+  id: string
+  name: string
   model: ModelInfo
   instructions?: string
   tools?: AssistantTool[]
diff --git a/src-tauri/src/core/threads.rs b/src-tauri/src/core/threads.rs
index 051837992..3554e287c 100644
--- a/src-tauri/src/core/threads.rs
+++ b/src-tauri/src/core/threads.rs
@@ -97,8 +97,8 @@ pub struct ImageContentValue {
 
 #[derive(Debug, Serialize, Deserialize, Clone)]
 pub struct ThreadAssistantInfo {
-    pub assistant_id: String,
-    pub assistant_name: String,
+    pub id: String,
+    pub name: String,
     pub model: ModelInfo,
     pub instructions: Option<String>,
     pub tools: Option<Vec<AssistantTool>>,
@@ -456,16 +456,16 @@ pub async fn modify_thread_assistant<R: Runtime>(
         serde_json::from_str(&data).map_err(|e| e.to_string())?
     };
     let assistant_id = assistant
-        .get("assistant_id")
+        .get("id")
         .and_then(|v| v.as_str())
-        .ok_or("Missing assistant_id")?;
+        .ok_or("Missing id")?;
     if let Some(assistants) = thread
         .get_mut("assistants")
         .and_then(|a: &mut serde_json::Value| a.as_array_mut())
     {
         if let Some(index) = assistants
             .iter()
-            .position(|a| a.get("assistant_id").and_then(|v| v.as_str()) == Some(assistant_id))
+            .position(|a| a.get("id").and_then(|v| v.as_str()) == Some(assistant_id))
         {
             assistants[index] = assistant.clone();
             let data = serde_json::to_string_pretty(&thread).map_err(|e| e.to_string())?;
diff --git a/web-app/src/containers/DropdownAssistant.tsx b/web-app/src/containers/DropdownAssistant.tsx
index 5c6b12c9a..51cdc4c7b 100644
--- a/web-app/src/containers/DropdownAssistant.tsx
+++ b/web-app/src/containers/DropdownAssistant.tsx
@@ -9,20 +9,25 @@ import {
 import { useAssistant } from '@/hooks/useAssistant'
 import AddEditAssistant from './dialogs/AddEditAssistant'
 import { IconCirclePlus, IconSettings } from '@tabler/icons-react'
+import { useThreads } from '@/hooks/useThreads'
 
 const DropdownAssistant = () => {
-  const { assistants, addAssistant, updateAssistant } = useAssistant()
+  const {
+    assistants,
+    currentAssistant,
+    addAssistant,
+    updateAssistant,
+    setCurrentAssistant,
+  } = useAssistant()
+  const { updateCurrentThreadAssistant } = useThreads()
   const [dropdownOpen, setDropdownOpen] = useState(false)
   const [dialogOpen, setDialogOpen] = useState(false)
   const [editingAssistantId, setEditingAssistantId] = useState<string | null>(
     null
   )
-  const [selectedAssistantId, setSelectedAssistantId] = useState<string | null>(
-    assistants[0]?.id || null
-  )
 
   const selectedAssistant =
-    assistants.find((a) => a.id === selectedAssistantId) || assistants[0]
+    assistants.find((a) => a.id === currentAssistant.id) || assistants[0]
 
   return (
     <>
@@ -63,7 +68,10 @@ const DropdownAssistant = () => {
               <DropdownMenuItem className="flex justify-between items-center">
                 <span
                   className="truncate text-main-view-fg/70 flex-1 cursor-pointer"
-                  onClick={() => setSelectedAssistantId(assistant.id)}
+                  onClick={() => {
+                    setCurrentAssistant(assistant)
+                    updateCurrentThreadAssistant(assistant)
+                  }}
                 >
                   {assistant.name}
                 </span>
diff --git a/web-app/src/hooks/useAssistant.ts b/web-app/src/hooks/useAssistant.ts
index 1e2e0835e..e22083029 100644
--- a/web-app/src/hooks/useAssistant.ts
+++ b/web-app/src/hooks/useAssistant.ts
@@ -2,24 +2,17 @@ import { localStoregeKey } from '@/constants/localStorage'
 import { create } from 'zustand'
 import { persist } from 'zustand/middleware'
 
-export type Assistant = {
-  avatar?: string
-  id: string
-  name: string
-  created_at: number
-  description?: string
-  instructions: string
-  parameters: Record<string, unknown>
-}
 
 interface AssistantState {
   assistants: Assistant[]
+  currentAssistant: Assistant
   addAssistant: (assistant: Assistant) => void
   updateAssistant: (assistant: Assistant) => void
   deleteAssistant: (id: string) => void
+  setCurrentAssistant: (assistant: Assistant) => void
 }
 
-const defaultAssistant: Assistant = {
+export const defaultAssistant: Assistant = {
   avatar: '',
   id: 'jan',
   name: 'Jan',
@@ -33,6 +26,7 @@ export const useAssistant = create<AssistantState>()(
   persist(
     (set, get) => ({
       assistants: [defaultAssistant],
+      currentAssistant: defaultAssistant,
       addAssistant: (assistant) =>
         set({ assistants: [...get().assistants, assistant] }),
       updateAssistant: (assistant) =>
@@ -43,6 +37,9 @@ export const useAssistant = create<AssistantState>()(
         }),
       deleteAssistant: (id) =>
         set({ assistants: get().assistants.filter((a) => a.id !== id) }),
+      setCurrentAssistant: (assistant) => {
+        set({ currentAssistant: assistant })
+      },
     }),
     {
       name: localStoregeKey.assistant,
diff --git a/web-app/src/hooks/useChat.ts b/web-app/src/hooks/useChat.ts
index 12effe82d..17220f88d 100644
--- a/web-app/src/hooks/useChat.ts
+++ b/web-app/src/hooks/useChat.ts
@@ -18,10 +18,12 @@ import {
 } from '@/lib/completion'
 import { CompletionMessagesBuilder } from '@/lib/messages'
 import { ChatCompletionMessageToolCall } from 'openai/resources'
+import { useAssistant } from './useAssistant'
 
 export const useChat = () => {
   const { prompt, setPrompt } = usePrompt()
   const { tools } = useAppState()
+  const { currentAssistant } = useAssistant()
 
   const { getProviderByName, selectedModel, selectedProvider } =
     useModelProvider()
@@ -43,7 +45,8 @@ export const useChat = () => {
           id: selectedModel?.id ?? defaultModel(selectedProvider),
           provider: selectedProvider,
         },
-        prompt
+        prompt,
+        currentAssistant
       )
       router.navigate({
         to: route.threadsDetail,
@@ -58,6 +61,7 @@ export const useChat = () => {
     router,
     selectedModel?.id,
     selectedProvider,
+    currentAssistant,
   ])
 
   const sendMessage = useCallback(
@@ -79,6 +83,8 @@ export const useChat = () => {
         }
 
         const builder = new CompletionMessagesBuilder()
+        if (currentAssistant?.instructions?.length > 0)
+          builder.addSystemMessage(currentAssistant?.instructions || '')
         // REMARK: Would it possible to not attach the entire message history to the request?
         // TODO: If not amend messages history here
         builder.addUserMessage(message)
@@ -143,9 +149,10 @@ export const useChat = () => {
       addMessage,
       setPrompt,
       selectedModel,
-      tools,
+      currentAssistant?.instructions,
       setAbortController,
       updateLoadingModel,
+      tools,
     ]
   )
 
diff --git a/web-app/src/hooks/useThreads.ts b/web-app/src/hooks/useThreads.ts
index f91dedf95..f83a9d69d 100644
--- a/web-app/src/hooks/useThreads.ts
+++ b/web-app/src/hooks/useThreads.ts
@@ -17,9 +17,14 @@ type ThreadState = {
   deleteAllThreads: () => void
   unstarAllThreads: () => void
   setCurrentThreadId: (threadId?: string) => void
-  createThread: (model: ThreadModel, title?: string) => Promise<Thread>
+  createThread: (
+    model: ThreadModel,
+    title?: string,
+    assistant?: Assistant
+  ) => Promise<Thread>
   updateCurrentThreadModel: (model: ThreadModel) => void
   getFilteredThreads: (searchTerm: string) => Thread[]
+  updateCurrentThreadAssistant: (assistant: Assistant) => void
   searchIndex: Fuse<Thread> | null
 }
 
@@ -152,18 +157,18 @@ export const useThreads = create<ThreadState>()(
       setCurrentThreadId: (threadId) => {
         set({ currentThreadId: threadId })
       },
-      createThread: async (model, title) => {
+      createThread: async (model, title, assistant) => {
         const newThread: Thread = {
           id: ulid(),
           title: title ?? 'New Thread',
           model,
           order: 1,
           updated: Date.now() / 1000,
+          assistants: assistant ? [assistant] : [],
         }
         set((state) => ({
           searchIndex: new Fuse(Object.values(state.threads), fuseOptions),
         }))
-        console.log('newThread', newThread)
         return await createThread(newThread).then((createdThread) => {
           set((state) => ({
             threads: {
@@ -175,6 +180,26 @@ export const useThreads = create<ThreadState>()(
           return createdThread
         })
       },
+      updateCurrentThreadAssistant: (assistant) => {
+        set((state) => {
+          if (!state.currentThreadId) return { ...state }
+          const currentThread = state.getCurrentThread()
+          if (currentThread)
+            updateThread({
+              ...currentThread,
+              assistants: [{ ...assistant, model: currentThread.model }],
+            })
+          return {
+            threads: {
+              ...state.threads,
+              [state.currentThreadId as string]: {
+                ...state.threads[state.currentThreadId as string],
+                assistants: [assistant],
+              },
+            },
+          }
+        })
+      },
       updateCurrentThreadModel: (model) => {
         set((state) => {
           if (!state.currentThreadId) return { ...state }
diff --git a/web-app/src/lib/messages.ts b/web-app/src/lib/messages.ts
index 1175a6549..2f46b8eb0 100644
--- a/web-app/src/lib/messages.ts
+++ b/web-app/src/lib/messages.ts
@@ -1,11 +1,30 @@
 import { ChatCompletionMessageParam } from 'token.js'
 import { ChatCompletionMessageToolCall } from 'openai/resources'
 
+/**
+ * @fileoverview Helper functions for creating chat completion request.
+ * These functions are used to create chat completion request objects
+ */
 export class CompletionMessagesBuilder {
   private messages: ChatCompletionMessageParam[] = []
 
   constructor() {}
 
+  /**
+   * Add a system message to the messages array.
+   * @param content - The content of the system message.
+   */
+  addSystemMessage(content: string) {
+    this.messages.push({
+      role: 'system',
+      content: content,
+    })
+  }
+
+  /**
+   * Add a user message to the messages array.
+   * @param content - The content of the user message.
+   */
   addUserMessage(content: string) {
     this.messages.push({
       role: 'user',
@@ -13,15 +32,30 @@ export class CompletionMessagesBuilder {
     })
   }
 
-  addAssistantMessage(content: string, refusal?: string, calls?: ChatCompletionMessageToolCall[]) {
+  /**
+   * Add an assistant message to the messages array.
+   * @param content - The content of the assistant message.
+   * @param refusal - Optional refusal message.
+   * @param calls - Optional tool calls associated with the message.
+   */
+  addAssistantMessage(
+    content: string,
+    refusal?: string,
+    calls?: ChatCompletionMessageToolCall[]
+  ) {
     this.messages.push({
       role: 'assistant',
       content: content,
       refusal: refusal,
-      tool_calls: calls
+      tool_calls: calls,
     })
   }
 
+  /**
+   * Add a tool message to the messages array.
+   * @param content - The content of the tool message.
+   * @param toolCallId - The ID of the tool call associated with the message.
+   */
   addToolMessage(content: string, toolCallId: string) {
     this.messages.push({
       role: 'tool',
@@ -30,6 +64,10 @@ export class CompletionMessagesBuilder {
     })
   }
 
+  /**
+   * Return the messages array.
+   * @returns The array of chat completion messages.
+   */
   getMessages(): ChatCompletionMessageParam[] {
     return this.messages
   }
diff --git a/web-app/src/routes/index.tsx b/web-app/src/routes/index.tsx
index 667964640..8297c1022 100644
--- a/web-app/src/routes/index.tsx
+++ b/web-app/src/routes/index.tsx
@@ -15,6 +15,8 @@ type SearchParams = {
   }
 }
 import DropdownAssistant from '@/containers/DropdownAssistant'
+import { useEffect } from 'react'
+import { useThreads } from '@/hooks/useThreads'
 
 export const Route = createFileRoute(route.home as any)({
   component: Index,
@@ -28,6 +30,7 @@ function Index() {
   const { providers } = useModelProvider()
   const search = useSearch({ from: route.home as any })
   const selectedModel = search.model
+  const { setCurrentThreadId } = useThreads()
 
   // Conditional to check if there are any valid providers
   // required min 1 api_key or 1 model in llama.cpp
@@ -37,6 +40,10 @@ function Index() {
       (provider.provider === 'llama.cpp' && provider.models.length)
   )
 
+  useEffect(() => {
+    setCurrentThreadId(undefined)
+  }, [setCurrentThreadId])
+
   if (!hasValidProviders) {
     return <SetupScreen />
   }
diff --git a/web-app/src/routes/threads/$threadId.tsx b/web-app/src/routes/threads/$threadId.tsx
index d99350ca6..b02e3183e 100644
--- a/web-app/src/routes/threads/$threadId.tsx
+++ b/web-app/src/routes/threads/$threadId.tsx
@@ -16,6 +16,7 @@ import { useMessages } from '@/hooks/useMessages'
 import { fetchMessages } from '@/services/messages'
 import { useAppState } from '@/hooks/useAppState'
 import DropdownAssistant from '@/containers/DropdownAssistant'
+import { useAssistant } from '@/hooks/useAssistant'
 
 // as route.threadsDetail
 export const Route = createFileRoute('/threads/$threadId')({
@@ -28,6 +29,7 @@ function ThreadDetail() {
   const [isAtBottom, setIsAtBottom] = useState(true)
   const lastScrollTopRef = useRef(0)
   const { currentThreadId, getThreadById, setCurrentThreadId } = useThreads()
+  const { setCurrentAssistant, assistants } = useAssistant()
   const { setMessages } = useMessages()
   const { streamingContent, loadingModel } = useAppState()
 
@@ -45,9 +47,16 @@ function ThreadDetail() {
   const isFirstRender = useRef(true)
 
   useEffect(() => {
-    if (currentThreadId !== threadId) setCurrentThreadId(threadId)
+    if (currentThreadId !== threadId) {
+      setCurrentThreadId(threadId)
+      const assistant = assistants.find(
+        (assistant) => assistant.id === thread?.assistants?.[0]?.id
+      )
+      if (assistant) setCurrentAssistant(assistant)
+    }
+
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [threadId, currentThreadId])
+  }, [threadId, currentThreadId, assistants])
 
   useEffect(() => {
     fetchMessages(threadId).then((fetchedMessages) => {
diff --git a/web-app/src/services/threads.ts b/web-app/src/services/threads.ts
index 1af6cfb1e..4b26779ce 100644
--- a/web-app/src/services/threads.ts
+++ b/web-app/src/services/threads.ts
@@ -1,3 +1,4 @@
+import { defaultAssistant } from '@/hooks/useAssistant'
 import { ExtensionManager } from '@/lib/extension'
 import { ConversationalExtension, ExtensionTypeEnum } from '@janhq/core'
 
@@ -20,9 +21,10 @@ export const fetchThreads = async (): Promise<Thread[]> => {
             order: e.metadata?.order,
             isFavorite: e.metadata?.is_favorite,
             model: {
-              id: e.assistants?.[0]?.model.id,
-              provider: e.assistants?.[0]?.model.engine,
+              id: e.assistants?.[0]?.model?.id,
+              provider: e.assistants?.[0]?.model?.engine,
             },
+            assistants: e.assistants ?? [defaultAssistant],
           } as Thread
         })
       })
@@ -50,8 +52,8 @@ export const createThread = async (thread: Thread): Promise<Thread> => {
               id: thread.model?.id ?? '*',
               engine: thread.model?.provider ?? 'llama.cpp',
             },
-            assistant_id: 'jan',
-            assistant_name: 'Jan',
+            id: 'jan',
+            name: 'Jan',
           },
         ],
         metadata: {
@@ -63,10 +65,11 @@ export const createThread = async (thread: Thread): Promise<Thread> => {
           ...e,
           updated: e.updated,
           model: {
-            id: e.assistants?.[0]?.model.id,
-            provider: e.assistants?.[0]?.model.engine,
+            id: e.assistants?.[0]?.model?.id,
+            provider: e.assistants?.[0]?.model?.engine,
           },
           order: 1,
+          assistants: e.assistants ?? [defaultAssistant],
         } as Thread
       })
       .catch(() => thread) ?? thread
@@ -82,14 +85,24 @@ export const updateThread = (thread: Thread) => {
     .get<ConversationalExtension>(ExtensionTypeEnum.Conversational)
     ?.modifyThread({
       ...thread,
-      assistants: [
+      assistants: thread.assistants?.map((e) => {
+        return {
+          model: {
+            id: thread.model?.id ?? '*',
+            engine: thread.model?.provider ?? 'llama.cpp',
+          },
+          id: e.id,
+          name: e.name,
+          instructions: e.instructions,
+        }
+      }) ?? [
         {
           model: {
             id: thread.model?.id ?? '*',
-            engine: (thread.model?.provider ?? 'llama.cpp'),
+            engine: thread.model?.provider ?? 'llama.cpp',
           },
-          assistant_id: 'jan',
-          assistant_name: 'Jan',
+          id: 'jan',
+          name: 'Jan',
         },
       ],
       metadata: {
diff --git a/web-app/src/types/threads.d.ts b/web-app/src/types/threads.d.ts
index e76e4b519..4f15039a5 100644
--- a/web-app/src/types/threads.d.ts
+++ b/web-app/src/types/threads.d.ts
@@ -31,11 +31,12 @@ type ThreadContent = {
 type ChatCompletionRole = 'system' | 'assistant' | 'user' | 'tool'
 
 type ThreadModel = {
-    id: string
-    provider: string
-  }
+  id: string
+  provider: string
+}
 
 type Thread = {
+  assistants?: ThreadAssistantInfo[]
   id: string
   title: string
   isFavorite?: boolean
@@ -44,3 +45,13 @@ type Thread = {
   updated: number
   order?: number
 }
+
+type Assistant = {
+  avatar?: string
+  id: string
+  name: string
+  created_at: number
+  description?: string
+  instructions: string
+  parameters: Record<string, unknown>
+}