STIR/SHAKEN for sales teams: what attestation means for your calls
STIR/SHAKEN decides which calls are trusted and which get labelled. The practical question is what attestation the calls you place actually carry.
STIR/SHAKEN is the framework US carriers use to cryptographically sign voice calls so the number displayed is the number that placed them. Every call carries an attestation level — A, B or C — describing how much the originating provider can vouch for. Lower attestation makes labelling and blocking more likely, independent of who is calling.
What it is
STIR/SHAKEN is the caller ID authentication regime US carriers were required to implement under the TRACED Act. STIR is the technical standard for signing calls; SHAKEN is the governance framework that says how providers are supposed to do it. When a call is placed, the originating provider signs it with a digital certificate, and the terminating provider can verify that the number displayed is the number that actually placed the call.
Its purpose is narrow and worth holding onto: it stops spoofing — calls pretending to be from a number they are not. It does not judge whether a call is wanted. That distinction is the source of most of the confusion around it.
The three attestation levels
Attestation describes the provider’s knowledge at signing time, not the quality of your calls. A well-run team on numbers that were never verified sits at B or C, and an impeccable call record does not move a number past where the provider placed it.
| Level | What the provider vouches for | Typical for |
|---|---|---|
| A — full | It knows the customer, and that they are authorized to use the number | Direct numbers a business holds with a provider that knows it |
| B — partial | The customer is known, but the number’s provenance is not fully verified | Numbers provisioned without full verification |
| C — gateway | Neither the customer nor the number can be vouched for | Traffic handed off through an intermediary |
What it changes for an outbound team
For an outbound team, attestation is decided by how your numbers are provisioned, and most teams never ask. Numbers a business holds directly with a carrier that knows it can be signed at A. Numbers obtained through an aggregator, an API reseller or a chain of intermediaries tend to arrive at B or C — because the originating provider can only vouch for the traffic it can see.
This is the fair question to put to any dialer vendor: what attestation level do calls placed through you carry? The answer will be a letter, and a vendor that does not know its own answer has effectively answered C.
A fully-attested call is also the foundation for branded caller ID — displaying a verified company name instead of a bare number. Branding only rides on top of attestation; it is not a substitute for it.
Why labelling still happens
Here is the part that keeps things honest: STIR/SHAKEN authenticates a call, it does not legitimise it. A fully-attested call from a number that behaves like a spammer still gets labelled, because attestation and reputation are scored by separate systems. Analytics read behavior — volume, duration, answer rate, complaints — and attestation is one input among several.
So high attestation is necessary for clean deliverability at scale and nowhere near sufficient. The team that assumes "we are A-attested, we are fine" is about to be reintroduced to its answer rate.
What to ask your dialer
Three questions, in order. What attestation level do calls through you carry? Are the numbers you provide held directly, or routed through intermediaries? And do you support registered, branded caller ID on top of attestation?
Numbers obtained through a provider that can attest fully behave differently from numbers routed through intermediaries — that difference is measurable in labelling and answer rates, and it is the part of STIR/SHAKEN that outbound teams can actually act on.
Common questions
What is STIR/SHAKEN?
It is the framework US carriers use to cryptographically verify that a call comes from the number it displays. STIR is the technical standard for signing calls; SHAKEN is the governance framework for how providers implement it. It was mandated under the TRACED Act, and it does not by itself decide whether a call is labelled as spam.
What do the attestation levels A, B and C mean?
They describe how much the originating provider can vouch for a call. A (full) means the provider knows the customer and that they are authorized to use the number; B (partial) means the customer is known but the number’s provenance is not fully verified; C (gateway) means neither can be vouched for. Lower levels are treated more skeptically by downstream carriers.
Will STIR/SHAKEN stop my calls being blocked?
Not by itself. Attestation authenticates who placed the call; labelling is decided by separate analytics that score behavior — volume, duration, answer rate and complaints. A fully-attested number that behaves like spam is still labelled. High attestation is necessary and not sufficient.
How do I know what attestation my calls carry?
Ask your dialer or number provider directly: what attestation level do calls placed through you carry, and are the numbers held directly or routed through intermediaries? The answer is a letter and a provisioning fact, not a marketing claim.
Does STIR/SHAKEN apply to SMS?
No. STIR/SHAKEN authenticates voice calls. Text messaging is governed by a separate regime — A2P 10DLC — which registers the brand and each campaign rather than signing individual calls. The two are frequently conflated in vendor material.
Sources
Checked on 19 August 2026. Regulatory text is quoted from the regulation itself rather than from a summary of it. If something here is wrong or has gone stale, that is a bug: tell us and we will correct it.
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