diff --git a/bridge_integration_test.go b/bridge_integration_test.go
index f8ef57e..7fb7885 100644
--- a/bridge_integration_test.go
+++ b/bridge_integration_test.go
@@ -605,7 +605,7 @@ func TestSimple(t *testing.T) {
 					// multiple messages in response to a single request.
 					id, err := tc.getResponseIDFunc(streaming, resp)
 					require.NoError(t, err, "failed to retrieve response ID")
-					require.Nil(t, uuid.Validate(id), "id is not a UUID")
+					require.Nilf(t, uuid.Validate(id), "%s is not a valid UUID", id)
 
 					require.GreaterOrEqual(t, len(recorderClient.tokenUsages), 1)
 					require.Equal(t, recorderClient.tokenUsages[0].MsgID, tc.expectedMsgID)
diff --git a/intercept_anthropic_messages_streaming.go b/intercept_anthropic_messages_streaming.go
index ef8aabd..5f2393a 100644
--- a/intercept_anthropic_messages_streaming.go
+++ b/intercept_anthropic_messages_streaming.go
@@ -15,6 +15,7 @@ import (
 	"github.com/coder/aibridge/mcp"
 	"github.com/google/uuid"
 	mcplib "github.com/mark3labs/mcp-go/mcp"
+	"github.com/tidwall/sjson"
 
 	"cdr.dev/slog"
 )
@@ -390,8 +391,7 @@ newStream:
 			}
 
 			// Overwrite response identifier since proxy obscures injected tool call invocations.
-			event.Message.ID = i.ID().String()
-			payload, err := i.marshal(event)
+			payload, err := i.marshalEvent(event)
 			if err != nil {
 				logger.Warn(ctx, "failed to marshal event", slog.Error(err), slog.F("event", event.RawJSON()))
 				lastErr = fmt.Errorf("marshal event: %w", err)
@@ -474,6 +474,20 @@ newStream:
 	return interceptionErr
 }
 
+func (s *AnthropicMessagesStreamingInterception) marshalEvent(event anthropic.MessageStreamEventUnion) ([]byte, error) {
+	sj, err := sjson.Set(event.RawJSON(), "message.id", s.ID().String())
+	if err != nil {
+		return nil, fmt.Errorf("marshal event id failed: %w", err)
+	}
+
+	sj, err = sjson.Set(sj, "usage.output_tokens", event.Usage.OutputTokens)
+	if err != nil {
+		return nil, fmt.Errorf("marshal event usage failed: %w", err)
+	}
+
+	return s.encodeForStream([]byte(sj), event.Type), nil
+}
+
 func (s *AnthropicMessagesStreamingInterception) marshal(payload any) ([]byte, error) {
 	data, err := json.Marshal(payload)
 	if err != nil {