Last updated 26 August 2026. Written while evaluating quotes from three RCS aggregators for a live US launch. No vendor’s figures appear here — the structure is the same everywhere, and the structure is what surprises people.
Google defines an RCS conversation as a session, and every US aggregator inherits the definition. A session triggers when four messages are delivered within 24 hours, of which at least two are from the user and at least one is from you. The clock starts at the first delivered message, in either direction, and runs for 24 hours regardless of what happens next.
Once triggered, the session fee covers everything inside the window. Twenty messages cost the same as four.
Read the trigger condition again, though, because the expensive half is the part you do not author: at least two messages from the user. Whether a conversation is billed as a cheap session or as a pile of individual messages is decided by whether the person on the other end replies twice. Not by your volume, your commitment, or your negotiation.
RCS rate cards quote a price “per MT/MO” — mobile-terminated and mobile-originated, meaning sent and received. Both directions bill.
On US SMS, inbound is usually free. So if your product is built on people replying — surveys, check-ins, support, scheduling — moving to RCS does not just add a per-message premium. It starts charging you for the half of the traffic that used to be free.
What counts as a chargeable inbound varies slightly but generally includes freeform text, a tap on a reply chip, and a location share. Which means a chip tap is a billable event, and a carousel offering four chips per card is offering several of them.
This is the part that reliably surprises people, so it is worth working through.
Take a three-question survey. Someone who answers all three produces three inbound and three outbound messages: the session triggers, and you pay one session fee.
Someone who answers once produces one inbound and two outbound. Three messages, only one from the user — no trigger. That conversation bills per message, and on typical US rate cards three individual messages cost more than one session.
| Outcome | Messages | Session? | Billed as |
|---|---|---|---|
| Completed survey | 6 | Yes | One session fee |
| Answered once, abandoned | 3 | No | Three messages — often more than the session |
| Never answered | 1–2 | No | Per message |
So your worst-engaged conversations are your most expensive per conversation. Every improvement to completion rate is a cost reduction as well as a product win, and any quote you model on “messages per month” will be wrong in the direction that hurts.
Carrier pass-through fees sit on top of whatever your aggregator charges, and they are published — most aggregators host a schedule you can read before signing. Read it, because the spread is large. Across the US networks, per-session carrier fees currently differ by more than a factor of six between the cheapest and most expensive, and the two most expensive are not the smallest networks.
You cannot route around this. The recipient’s carrier is a property of the recipient. Two identical conversations can differ several-fold in cost, so your blended rate depends on the carrier mix of your audience — which means a pilot with one audience can mislead you about the economics of another.
One consequence worth planning for: a quote is not a number, it is a distribution. Ask for the pass-through schedule and compute a blended figure against your own audience rather than accepting a headline rate.
Rate cards separate basic/rich messages from rich media — anything carrying a file, and typically anything carrying a card. The media rate commonly runs around double the basic one, in both directions, and at least one US carrier meters message size above a few megabytes on top of that.
This matters less than it looks inside a triggered session, where the session fee covers everything. It matters a lot on conversations that never trigger — which, from section 3, are exactly your low-engagement ones. A rich carousel sent to someone who never replies is the most expensive single message you can send.
A quote will foreground the per-message and per-session rates, because that is what you asked about. For most businesses starting out, those are not the dominant line. The ones that are:
Every quote we have read lists a session rate and a per-message rate, and none of them states which applies when a session triggers. Does the session fee replace per-message billing inside the window, or sit on top of it?
Carrier schedules generally say the session covers all messages within it. Aggregator proposals often say nothing at all. The difference is roughly 2–3× your total RCS bill, so it is worth an email before it is worth a signature.
Every number above collapses into one question: what fraction of your conversations get two replies? That single figure decides whether you are buying sessions or messages, and it is measurable from traffic you already send — including SMS traffic, since the trigger is about human behaviour rather than the channel.
Count conversations with four or more total messages, at least one outbound and at least two inbound, inside a 24-hour window. That is the trigger, applied to history you already have. A business at 70% will have a very different bill from one at 20%, on the same rate card and the same volume.
Every conversation reports whether it triggered a session, so the number that decides your bill is a field rather than an estimate. RCS with automatic SMS fallback, an MCP server your agent can drive directly, and carrier-compliance onboarding underneath.
Get a free sandbox key — no card, no compliance wait — or read the agent-facing API reference.
Written by the team building Cadence, from quotes gathered for a live US RCS launch in 2026. Structure and ratios only — no vendor’s confidential pricing appears here. Carrier fees change; the schedules are published, so check them yourself before signing anything.
Its companion covers the fees that never appear on a rate card: per-agent charges, vetting renewals and pass-through fines. Choosing between channels first? RCS vs SMS. And the first two problems come earlier: nine undocumented traps in Google’s RBM API that get an agent rejected, and why an approved agent still reaches nobody until a carrier agreement exists.