diff --git a/chat.go b/chat.go
index 995860c4..3a79b890 100644
--- a/chat.go
+++ b/chat.go
@@ -262,7 +262,7 @@ type ChatCompletionRequest struct {
 	// Controls effort on reasoning for reasoning models. It can be set to "low", "medium", or "high".
 	ReasoningEffort string `json:"reasoning_effort,omitempty"`
 	// Metadata to store with the completion.
-	Metadata map[string]string `json:"metadata,omitempty"`
+	Metadata map[string]any `json:"metadata,omitempty"`
 }
 
 type StreamOptions struct {
diff --git a/messages.go b/messages.go
index 3852d2e3..31844ef8 100644
--- a/messages.go
+++ b/messages.go
@@ -162,7 +162,7 @@ func (c *Client) RetrieveMessage(
 func (c *Client) ModifyMessage(
 	ctx context.Context,
 	threadID, messageID string,
-	metadata map[string]string,
+	metadata map[string]any,
 ) (msg Message, err error) {
 	urlSuffix := fmt.Sprintf("/threads/%s/%s/%s", threadID, messagesSuffix, messageID)
 	req, err := c.newRequest(ctx, http.MethodPost, c.fullURL(urlSuffix),
diff --git a/messages_test.go b/messages_test.go
index b25755f9..3abc5871 100644
--- a/messages_test.go
+++ b/messages_test.go
@@ -233,7 +233,7 @@ func TestMessages(t *testing.T) {
 	}
 
 	msg, err = client.ModifyMessage(ctx, threadID, messageID,
-		map[string]string{
+		map[string]any{
 			"foo": "bar",
 		})
 	checks.NoError(t, err, "ModifyMessage error")