Should I use an iMessage API or an RCS API?

Since Apple added RCS support in iOS 18, this question comes up in every messaging architecture discussion. The two options look similar on a feature list — rich media, typing indicators, read receipts, delivery signals — and are completely different in the ways that matter.

The difference in one table

Choosing by what you are optimising for

The answer most teams land on

Use both, behind one interface. The provider decides per recipient: iMessage where it will land blue, RCS where the device supports it, SMS underneath as the floor. Several vendors already ship exactly this, which is why single-channel thinking is usually the wrong frame.

// Your application should not know or care which channel was used.
// It asks for a message to be delivered; the layer below picks the road.
type Channel = "imessage" | "rcs" | "sms";
 
export async function notify(to: string, text: string) {
  const result = await messaging.send({
    to,
    text,
    // Order matters: try the highest-trust channel first, fall down.
    preferChannels: ["imessage", "rcs", "sms"] satisfies Channel[],
  });
 
  // Record which channel actually delivered — this is the number you
  // need to compare response rates honestly across channels.
  await analytics.track("message_sent", {
    channel: result.channel,
    message_id: result.id,
  });
 
  return result;
}

Tracking the delivered channel is what lets you answer the question everyone eventually asks — whether the blue bubble is actually worth its price. Set the attribution up properly with UTM tagging for text messages and measuring ROI of texting.

The consumer-side comparison, without the API framing, is in iMessage vs RCS.