diff --git a/chat.go b/chat.go
index 0bb2e98ee..f364c4b7e 100644
--- a/chat.go
+++ b/chat.go
@@ -81,17 +81,26 @@ type ChatMessageImageURL struct {
 	Detail ImageURLDetail `json:"detail,omitempty"`
 }
 
+// ChatMessageFile is a placeholder for file parts in chat messages.
+type ChatMessageFile struct {
+	FileID   string `json:"file_id,omitempty"`
+	FileName string `json:"filename,omitempty"`
+	FileData string `json:"file_data,omitempty"` // Base64 encoded file data
+}
+
 type ChatMessagePartType string
 
 const (
 	ChatMessagePartTypeText     ChatMessagePartType = "text"
 	ChatMessagePartTypeImageURL ChatMessagePartType = "image_url"
+	ChatMessagePartTypeFile     ChatMessagePartType = "file"
 )
 
 type ChatMessagePart struct {
 	Type     ChatMessagePartType  `json:"type,omitempty"`
 	Text     string               `json:"text,omitempty"`
 	ImageURL *ChatMessageImageURL `json:"image_url,omitempty"`
+	File     *ChatMessageFile     `json:"file,omitempty"`
 }
 
 type ChatCompletionMessage struct {
diff --git a/chat_test.go b/chat_test.go
index 172ce0740..ad9e77315 100644
--- a/chat_test.go
+++ b/chat_test.go
@@ -677,6 +677,14 @@ func TestMultipartChatCompletions(t *testing.T) {
 							Detail: openai.ImageURLDetailLow,
 						},
 					},
+					{
+						Type: openai.ChatMessagePartTypeFile,
+						File: &openai.ChatMessageFile{
+							FileID:   "file-123",
+							FileName: "test.txt",
+							FileData: "dGVzdCBmaWxlIGNvbnRlbnQ=", // base64 encoded "test file content"
+						},
+					},
 				},
 			},
 		},
@@ -687,7 +695,8 @@ func TestMultipartChatCompletions(t *testing.T) {
 func TestMultipartChatMessageSerialization(t *testing.T) {
 	jsonText := `[{"role":"system","content":"system-message"},` +
 		`{"role":"user","content":[{"type":"text","text":"nice-text"},` +
-		`{"type":"image_url","image_url":{"url":"URL","detail":"high"}}]}]`
+		`{"type":"image_url","image_url":{"url":"URL","detail":"high"}},` +
+		`{"type":"file","file":{"file_id":"file-123","filename":"test.txt","file_data":"dGVzdA=="}}]}]`
 
 	var msgs []openai.ChatCompletionMessage
 	err := json.Unmarshal([]byte(jsonText), &msgs)
@@ -700,7 +709,7 @@ func TestMultipartChatMessageSerialization(t *testing.T) {
 	if msgs[0].Role != "system" || msgs[0].Content != "system-message" || msgs[0].MultiContent != nil {
 		t.Errorf("invalid user message: %v", msgs[0])
 	}
-	if msgs[1].Role != "user" || msgs[1].Content != "" || len(msgs[1].MultiContent) != 2 {
+	if msgs[1].Role != "user" || msgs[1].Content != "" || len(msgs[1].MultiContent) != 3 {
 		t.Errorf("invalid user message")
 	}
 	parts := msgs[1].MultiContent
@@ -710,6 +719,10 @@ func TestMultipartChatMessageSerialization(t *testing.T) {
 	if parts[1].Type != "image_url" || parts[1].ImageURL.URL != "URL" || parts[1].ImageURL.Detail != "high" {
 		t.Errorf("invalid image_url part")
 	}
+	if parts[2].Type != "file" || parts[2].File.FileID != "file-123" ||
+		parts[2].File.FileName != "test.txt" || parts[2].File.FileData != "dGVzdA==" {
+		t.Errorf("invalid file part: %v", parts[2])
+	}
 
 	s, err := json.Marshal(msgs)
 	if err != nil {
@@ -756,6 +769,103 @@ func TestMultipartChatMessageSerialization(t *testing.T) {
 	}
 }
 
+func TestChatMessageFile(t *testing.T) {
+	// Test file part with FileID
+	filePart := openai.ChatMessagePart{
+		Type: openai.ChatMessagePartTypeFile,
+		File: &openai.ChatMessageFile{
+			FileID: "file-abc123",
+		},
+	}
+
+	// Test serialization
+	data, err := json.Marshal(filePart)
+	if err != nil {
+		t.Fatalf("Expected no error: %s", err)
+	}
+
+	expected := `{"type":"file","file":{"file_id":"file-abc123"}}`
+	result := strings.ReplaceAll(string(data), " ", "")
+	if result != expected {
+		t.Errorf("Expected %s, got %s", expected, result)
+	}
+
+	// Test deserialization
+	var parsedPart openai.ChatMessagePart
+	err = json.Unmarshal(data, &parsedPart)
+	if err != nil {
+		t.Fatalf("Expected no error: %s", err)
+	}
+
+	if parsedPart.Type != openai.ChatMessagePartTypeFile {
+		t.Errorf("Expected type %s, got %s", openai.ChatMessagePartTypeFile, parsedPart.Type)
+	}
+	if parsedPart.File == nil {
+		t.Fatal("Expected File to be non-nil")
+	}
+	if parsedPart.File.FileID != "file-abc123" {
+		t.Errorf("Expected FileID %s, got %s", "file-abc123", parsedPart.File.FileID)
+	}
+
+	// Test file part with all fields
+	filePartComplete := openai.ChatMessagePart{
+		Type: openai.ChatMessagePartTypeFile,
+		File: &openai.ChatMessageFile{
+			FileID:   "file-xyz789",
+			FileName: "document.pdf",
+			FileData: "JVBERi0xLjQK", // base64 for "%PDF-1.4\n"
+		},
+	}
+
+	data, err = json.Marshal(filePartComplete)
+	if err != nil {
+		t.Fatalf("Expected no error: %s", err)
+	}
+
+	expected = `{"type":"file","file":{"file_id":"file-xyz789","filename":"document.pdf","file_data":"JVBERi0xLjQK"}}`
+	result = strings.ReplaceAll(string(data), " ", "")
+	if result != expected {
+		t.Errorf("Expected %s, got %s", expected, result)
+	}
+
+	// Test deserialization of complete file part
+	var parsedCompleteFile openai.ChatMessagePart
+	err = json.Unmarshal(data, &parsedCompleteFile)
+	if err != nil {
+		t.Fatalf("Expected no error: %s", err)
+	}
+
+	if parsedCompleteFile.File.FileID != "file-xyz789" {
+		t.Errorf("Expected FileID %s, got %s", "file-xyz789", parsedCompleteFile.File.FileID)
+	}
+	if parsedCompleteFile.File.FileName != "document.pdf" {
+		t.Errorf("Expected FileName %s, got %s", "document.pdf", parsedCompleteFile.File.FileName)
+	}
+	if parsedCompleteFile.File.FileData != "JVBERi0xLjQK" {
+		t.Errorf("Expected FileData %s, got %s", "JVBERi0xLjQK", parsedCompleteFile.File.FileData)
+	}
+}
+
+func TestChatMessagePartTypeConstants(t *testing.T) {
+	// Test that the new file constant is properly defined
+	if openai.ChatMessagePartTypeFile != "file" {
+		t.Errorf("Expected ChatMessagePartTypeFile to be 'file', got %s", openai.ChatMessagePartTypeFile)
+	}
+
+	// Test all part type constants
+	expectedTypes := map[openai.ChatMessagePartType]string{
+		openai.ChatMessagePartTypeText:     "text",
+		openai.ChatMessagePartTypeImageURL: "image_url",
+		openai.ChatMessagePartTypeFile:     "file",
+	}
+
+	for constant, expected := range expectedTypes {
+		if string(constant) != expected {
+			t.Errorf("Expected %s to be %s, got %s", constant, expected, string(constant))
+		}
+	}
+}
+
 // handleChatCompletionEndpoint Handles the ChatGPT completion endpoint by the test server.
 func handleChatCompletionEndpoint(w http.ResponseWriter, r *http.Request) {
 	var err error