diff --git a/command/openai/api.go b/command/openai/api.go
index 61e3129a..06afb98d 100644
--- a/command/openai/api.go
+++ b/command/openai/api.go
@@ -11,6 +11,7 @@ import (
 const (
 	apiHost                  = "https://api.openai.com"
 	apiCompletionURL         = "/v1/chat/completions"
+	apiThreadsURL            = "/v1/threads"
 	apiDalleGenerateImageURL = "/v1/images/generations"
 )
 
@@ -25,14 +26,15 @@ var client = http.Client{
 	Timeout: 60 * time.Second,
 }
 
-func doRequest(cfg Config, apiEndpoint string, data []byte) (*http.Response, error) {
-	req, err := http.NewRequest("POST", cfg.APIHost+apiEndpoint, bytes.NewBuffer(data))
+func doRequest(cfg Config, method string, apiEndpoint string, data []byte) (*http.Response, error) {
+	req, err := http.NewRequest(method, cfg.APIHost+apiEndpoint, bytes.NewBuffer(data))
 	if err != nil {
 		return nil, err
 	}
 
 	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("Authorization", "Bearer "+cfg.APIKey)
+	req.Header.Set("OpenAI-Beta", "assistants=v1")
 
 	return client.Do(req)
 }
diff --git a/command/openai/assistant.go b/command/openai/assistant.go
new file mode 100644
index 00000000..7b637aff
--- /dev/null
+++ b/command/openai/assistant.go
@@ -0,0 +1,300 @@
+package openai
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/innogames/slack-bot/v2/bot/msg"
+	"github.com/innogames/slack-bot/v2/bot/storage"
+	"github.com/slack-go/slack"
+	"io"
+	"time"
+)
+
+// see https://platform.openai.com/docs/assistants/how-it-works
+
+type assistantThreadResponse struct {
+	Id string `json:"id"`
+}
+type assistantStartRun struct {
+	AssistantId string `json:"assistant_id"`
+}
+
+type run struct {
+	Id             string                  `json:"id"`
+	Status         string                  `json:"status"`
+	ThreadId       string                  `json:"thread_id"`
+	RequiredAction AssistantRequiredAction `json:"required_action"`
+}
+
+type AssistantRequiredAction struct {
+	Type               string `json:"type"`
+	SubmitToolsOutputs struct {
+		ToolCalls []struct {
+			Id       string `json:"id"`
+			Type     string `json:"type"`
+			Function struct {
+				Name      string `json:"name"`
+				Arguments string `json:"arguments"`
+			} `json:"function"`
+		} `json:"tool_calls"`
+	} `json:"submit_tool_outputs"`
+}
+
+type AssistantContent struct {
+	Type string `json:"type"`
+	Text struct {
+		Value string `json:"value"`
+	} `json:"text"`
+}
+
+func (c AssistantContent) GetText() string {
+	return c.Text.Value
+}
+
+type AssistantStartThreads struct {
+	Messages []ChatMessage `json:"messages"`
+}
+
+type AssistantChatMessage struct {
+	Id          string             `json:"id"`
+	Role        string             `json:"role"`
+	ChatMessage []AssistantContent `json:"content"`
+	RunId       string             `json:"run_id"`
+}
+type assistantFullResponse struct {
+	Data []AssistantChatMessage `json:"data"`
+}
+
+type AssistantToolsOutput struct {
+	ToolsOutput []struct {
+		ToolCallId string `json:"tool_call_id"`
+		Output     string `json:"output"`
+	} `json:"tool_outputs"`
+}
+
+func (c *openaiCommand) callCustomGPT(messages []ChatMessage, identifier string, message msg.Ref, text string) {
+	c.AddReaction(":coffee:", message)
+	defer c.RemoveReaction(":coffee:", message)
+
+	messages = append(messages, ChatMessage{
+		Role:    roleUser,
+		Content: text,
+	})
+
+	var threadId string
+	var err error
+	storage.Read("gpt-thread", identifier, &threadId)
+	if threadId == "" {
+		// start a new thread!
+		threadId, err = createAssistantThread(c.cfg, messages)
+		if err != nil {
+			c.ReplyError(message, err)
+			return
+		}
+		storage.Write("gpt-thread", identifier, threadId)
+	} else {
+		// attach slack messages to an existing thread
+		for _, newMessage := range messages {
+			// todo no API to bulk add?!
+			addMessage(c.cfg, threadId, newMessage)
+		}
+	}
+
+	// start the assistant and get a "run" object
+	run, err := assistantRun(c.cfg, threadId)
+	if err != nil {
+		c.ReplyError(message, err)
+		return
+	}
+
+	// wait till run is done or required more information from function calls!
+	// see https://platform.openai.com/docs/assistants/how-it-works/run-lifecycle
+	ticker := time.NewTicker(time.Second * 1)
+	defer ticker.Stop()
+	for range ticker.C {
+		run, err = getRun(c.cfg, run)
+		if err != nil || run.Status == "failed" || run.Status == "cancelled" || run.Status == "expired" {
+			c.ReplyError(message, fmt.Errorf("run failed with status %s", run.Status))
+			return
+		}
+
+		if run.Status == "completed" {
+			// we have the final answer!
+			break
+		}
+
+		if run.Status == "requires_action" {
+			// todo extract code!
+			fmt.Println(run.RequiredAction)
+			fmt.Println(run.RequiredAction.SubmitToolsOutputs)
+			tool := run.RequiredAction.SubmitToolsOutputs.ToolCalls[0]
+
+			var output string
+			if tool.Function.Name == "dall_image" {
+				// special function
+				prompt := tool.Function.Arguments
+				fmt.Println(prompt, "prompt")
+
+				images, _ := generateImages(c.cfg, prompt)
+				output = images[0].RevisedPrompt
+				go c.sendImageInSlack(images[0], message)
+			} else {
+				output = "Ticket: Fix issue in feature XYZ, status = open" // todo call function
+			}
+
+			sendToolsOutput(c.cfg, run, tool.Id, output)
+
+			// wait for new tick, as the API is handling the new information now...
+			continue
+		}
+	}
+
+	// todo only fetch the new messages for this run
+	respMessages, _ := listMessages(c.cfg, threadId)
+	for _, m := range respMessages {
+		if m.RunId != run.Id {
+			continue
+		}
+		fmt.Println(m.ChatMessage)
+		if m.Role != roleAssistant {
+			continue
+		}
+
+		// reply in thread
+		c.SendMessage(
+			message,
+			m.ChatMessage[0].GetText(),
+			slack.MsgOptionTS(message.GetTimestamp()),
+		)
+	}
+}
+
+/*
+func (c *openaiCommand) assistantUploadFile(cfg Config, file slack.File) error {
+	var buf bytes.Buffer
+	log.Infof("Downloading message attachment file %s", file.Name)
+
+	fmt.Println(file)
+
+	resp, err := doRequest(cfg, "POST", apiFilesURL, []byte("jolo"))
+	if err != nil {
+		return nil
+	}
+
+	r, _ := io.ReadAll(resp.Body)
+	fmt.Println(string(r))
+
+	return nil
+}
+*/
+
+func assistantRun(cfg Config, threadId string) (*run, error) {
+	fmt.Printf("run assistant %s\n", threadId)
+
+	assistantStartRun := assistantStartRun{
+		AssistantId: cfg.CustomGPT,
+	}
+
+	req, _ := json.Marshal(assistantStartRun)
+	resp, err := doRequest(cfg, "POST", apiThreadsURL+"/"+threadId+"/runs", req)
+	if err != nil {
+		return nil, err
+	}
+
+	run := &run{}
+	err = json.NewDecoder(resp.Body).Decode(run)
+	return run, err
+}
+
+func addMessage(cfg Config, threadId string, message ChatMessage) error {
+	fmt.Printf("add message to thread %s: %s\n", threadId, message)
+
+	req, _ := json.Marshal(message)
+	_, err := doRequest(cfg, "POST", apiThreadsURL+"/"+threadId+"/messages", req)
+
+	return err
+}
+
+func createAssistantThread(cfg Config, messages []ChatMessage) (string, error) {
+	fmt.Println("create thread")
+
+	req, _ := json.Marshal(AssistantStartThreads{
+		Messages: messages,
+	})
+	fmt.Println(string(req))
+	resp, err := doRequest(cfg, "POST", apiThreadsURL, req)
+	if err != nil {
+		return "", err
+	}
+	//r, _ := io.ReadAll(resp.Body)
+	//fmt.Println(string(r))
+	thread := assistantThreadResponse{}
+	err = json.NewDecoder(resp.Body).Decode(&thread)
+	if err != nil {
+		return "", err
+	}
+	fmt.Println(thread)
+
+	if thread.Id == "" {
+		return "", fmt.Errorf("failed to create thread")
+	}
+	return thread.Id, nil
+}
+
+func getRun(cfg Config, oldRun *run) (*run, error) {
+	fmt.Printf("get run %s %s\n", oldRun.ThreadId, oldRun.Id)
+	resp, err := doRequest(cfg, "GET", apiThreadsURL+"/"+oldRun.ThreadId+"/runs/"+oldRun.Id, nil)
+	if err != nil {
+		return oldRun, err
+	}
+
+	r, _ := io.ReadAll(resp.Body)
+	fmt.Println(string(r))
+
+	newRun := &run{}
+	err = json.Unmarshal(r, newRun)
+
+	return newRun, err
+}
+
+func listMessages(cfg Config, threadId string) ([]AssistantChatMessage, error) {
+	fmt.Printf("list messages %s \n", threadId)
+	resp, err := doRequest(cfg, "GET", apiThreadsURL+"/"+threadId+"/messages", nil)
+	if err != nil {
+		return []AssistantChatMessage{}, err
+	}
+
+	r, _ := io.ReadAll(resp.Body)
+	fmt.Println(string(r))
+
+	messages := assistantFullResponse{}
+	json.Unmarshal(r, &messages)
+
+	return messages.Data, nil
+}
+
+func sendToolsOutput(cfg Config, run *run, callId string, output string) error {
+	fmt.Printf("send tools output %s %s %s\n", run.ThreadId, run.Id, callId)
+
+	req, _ := json.Marshal(AssistantToolsOutput{
+		ToolsOutput: []struct {
+			ToolCallId string `json:"tool_call_id"`
+			Output     string `json:"output"`
+		}{
+			{
+				ToolCallId: callId,
+				Output:     output,
+			},
+		},
+	})
+	fmt.Println(string(req))
+	resp, err := doRequest(cfg, "POST", apiThreadsURL+"/"+run.ThreadId+"/runs/"+run.Id+"/submit_tool_outputs", req)
+	if err != nil {
+		return err
+	}
+
+	r, _ := io.ReadAll(resp.Body)
+	fmt.Println(string(r))
+
+	return err
+}
diff --git a/command/openai/chatgpt.go b/command/openai/chatgpt.go
index e9b6fc5d..42dae40a 100644
--- a/command/openai/chatgpt.go
+++ b/command/openai/chatgpt.go
@@ -26,7 +26,7 @@ func CallChatGPT(cfg Config, inputMessages []ChatMessage, stream bool) (<-chan s
 			Stream:      stream,
 			Messages:    inputMessages,
 		})
-		resp, err := doRequest(cfg, apiCompletionURL, jsonData)
+		resp, err := doRequest(cfg, "POST", apiCompletionURL, jsonData)
 		if err != nil {
 			messageUpdates <- err.Error()
 			return
diff --git a/command/openai/command.go b/command/openai/command.go
index 95f80295..f442d336 100644
--- a/command/openai/command.go
+++ b/command/openai/command.go
@@ -70,13 +70,13 @@ func (c *openaiCommand) GetMatcher() matcher.Matcher {
 // bot function which is called, when the user started a new conversation with openai/chatgpt
 func (c *openaiCommand) newConversation(match matcher.Result, message msg.Message) {
 	text := match.GetString(util.FullMatch)
-	c.startConversation(message.MessageRef, text)
+	c.startConversation(message, text)
 }
 
 func (c *openaiCommand) startConversation(message msg.Ref, text string) bool {
 	messageHistory := make([]ChatMessage, 0)
 
-	if c.cfg.InitialSystemMessage != "" {
+	if c.cfg.InitialSystemMessage != "" && c.cfg.CustomGPT == "" {
 		messageHistory = append(messageHistory, ChatMessage{
 			Role:    roleSystem,
 			Content: c.cfg.InitialSystemMessage,
@@ -135,7 +135,12 @@ func (c *openaiCommand) startConversation(message msg.Ref, text string) bool {
 		storageIdentifier = getIdentifier(message.GetChannel(), message.GetTimestamp())
 	}
 
-	c.callAndStore(messageHistory, storageIdentifier, message, text)
+	if c.cfg.CustomGPT != "" {
+		c.callCustomGPT(messageHistory, storageIdentifier, message, text)
+	} else {
+		// usual GPT-X model
+		c.callAndStore(messageHistory, storageIdentifier, message, text)
+	}
 	return true
 }
 
@@ -149,6 +154,13 @@ func (c *openaiCommand) reply(message msg.Ref, text string) bool {
 	// Load the chat history from storage.
 	identifier := getIdentifier(message.GetChannel(), message.GetThread())
 
+	var threadId string
+	storage.Read("gpt-thread", identifier, &threadId)
+	if threadId != "" {
+		c.callCustomGPT([]ChatMessage{}, identifier, message, text)
+		return true
+	}
+
 	var messages []ChatMessage
 	err := storage.Read(storageKey, identifier, &messages)
 	if err != nil || len(messages) == 0 {
diff --git a/command/openai/config.go b/command/openai/config.go
index b32c0504..a0910be2 100644
--- a/command/openai/config.go
+++ b/command/openai/config.go
@@ -32,6 +32,8 @@ type Config struct {
 	DalleModel          string `mapstructure:"dalle_model"`
 	DalleImageSize      string `mapstructure:"dalle_image_size"`
 	DalleNumberOfImages int    `mapstructure:"dalle_number_of_images"`
+
+	CustomGPT string `mapstructure:"custom_gpt"`
 }
 
 // IsEnabled checks if token is set
diff --git a/command/openai/dalle.go b/command/openai/dalle.go
index 16916483..05d45eb5 100644
--- a/command/openai/dalle.go
+++ b/command/openai/dalle.go
@@ -34,7 +34,7 @@ func (c *openaiCommand) dalleGenerateImage(match matcher.Result, message msg.Mes
 
 		startTime := time.Now()
 		for _, image := range images {
-			err := c.sendImageInSlack(image, message)
+			err := c.sendImageInSlack(image, message.MessageRef)
 			if err != nil {
 				c.ReplyError(
 					message,
@@ -42,11 +42,11 @@ func (c *openaiCommand) dalleGenerateImage(match matcher.Result, message msg.Mes
 				)
 			}
 		}
-		log.Infof("Uploading %d images took %s", len(images), time.Since(startTime))
+		log.Infof("Uploading %d images took %s", len(images), util.FormatDuration(time.Since(startTime)))
 	}()
 }
 
-func (c *openaiCommand) sendImageInSlack(image DalleResponseImage, message msg.Message) error {
+func (c *openaiCommand) sendImageInSlack(image DalleResponseImage, message msg.Ref) error {
 	req, err := http.NewRequest("GET", image.URL, nil)
 	if err != nil {
 		return err
@@ -60,8 +60,8 @@ func (c *openaiCommand) sendImageInSlack(image DalleResponseImage, message msg.M
 	_, err = c.SlackClient.UploadFile(slack.FileUploadParameters{
 		Filename:        "dalle.png",
 		Filetype:        "png",
-		Channels:        []string{message.Channel},
-		ThreadTimestamp: message.Timestamp,
+		Channels:        []string{message.GetChannel()},
+		ThreadTimestamp: message.GetTimestamp(),
 		Reader:          resp.Body,
 		InitialComment:  image.RevisedPrompt,
 	})
@@ -78,7 +78,7 @@ func generateImages(cfg Config, prompt string) ([]DalleResponseImage, error) {
 	})
 
 	start := time.Now()
-	resp, err := doRequest(cfg, apiDalleGenerateImageURL, jsonData)
+	resp, err := doRequest(cfg, "POST", apiDalleGenerateImageURL, jsonData)
 	if err != nil {
 		return nil, err
 	}
@@ -95,7 +95,7 @@ func generateImages(cfg Config, prompt string) ([]DalleResponseImage, error) {
 	}
 
 	log.WithField("model", cfg.DalleModel).
-		Infof("Dall-E image generation took %s", time.Since(start))
+		Infof("Dall-E image generation took %s", util.FormatDuration(time.Since(start)))
 	stats.Increase("openai_dalle_images", len(response.Data))
 
 	return response.Data, nil