What STIR/SHAKEN actually is
STIR and SHAKEN are two linked technical standards. STIR (Secure Telephone Identity Revisited) comes from the IETF and defines how to attach a signed token to a call. SHAKEN (Signature-based Handling of Asserted information using toKENs) comes from ATIS and the SIP Forum and defines how US carriers deploy it. The FCC describes the pair as a framework that lets calls on IP networks have their caller ID "signed" as legitimate by the originating carrier and validated by other carriers before the call reaches the consumer.
The FCC required voice service providers to implement it in the IP portions of their networks by June 30, 2021, and has since extended the obligation to gateway providers and to intermediate providers that receive unauthenticated calls directly from originating providers (FCC). Every provider, whether or not it must sign calls, has to file in the Robocall Mitigation Database.
How a signed call travels
- Your rep clicks dial.The dialer hands the call to a voice provider. That provider (or the one it buys from) is the one that places the call onto the IP network.
- The originating provider signs it.It creates an encrypted token called a PASSporT holding its own identity and signature, the calling number and an attestation level of A, B or C (FCC Call Branding FNPRM).
- Intermediate carriers pass it along.Any provider in the middle must pass the token downstream unaltered. If the call crosses an old non-IP (TDM) segment, the token can be lost, which is why the FCC is pushing non-IP authentication separately.
- The terminating carrier verifies it.The prospect's carrier checks the signature against the originating provider's certificate, then decides what to show on the handset and feeds the result into its call analytics.
Notice who is missing from that list: you. STIR/SHAKEN obligations fall on voice providers, not on the business making calls. Your influence comes from which provider signs your calls and what that provider knows about you and your numbers.
A, B and C attestation, in plain English
An attestation is the signing provider's statement about how well it knows its customer and that customer's right to use the number on the call. The FCC's 2026 proposal on attestation standards summarizes the ATIS definitions this way (Federal Register, July 2026):
| Level | What the signing provider asserts | Typical sales-team scenario |
|---|---|---|
| A (full) | It put the call on the IP network, has a direct authenticated relationship with the customer, and has verified that customer's right to use the calling number. | Your dialer or carrier issued the number to your account, or verified that you own a number you brought. |
| B (partial) | It put the call on the network and knows the customer, but has not verified the customer's right to that specific number. | You display a number the signing provider did not issue and has not verified, such as a main line hosted elsewhere. |
| C (gateway) | It is only the entry point for a call that started elsewhere and has no relationship with the caller, such as an international gateway. | Calls routed through an offshore or wholesale path before they reach a US network. |
The FCC puts the practical meaning plainly: calls with an A attestation "carry the best available assurance that the number has not been spoofed", while B and C calls "are not necessarily spoofed, but they lack the assurance of the highest attestation level" (FCC Call Branding FNPRM).
What STIR/SHAKEN does and does not do for answer rates
Most of what gets written for sales teams about STIR/SHAKEN overpromises. The FCC itself says the framework "can help consumers identify when the number displayed for an incoming call may be spoofed... but it does not let them know who is calling" (FCC fact sheet, October 2025). Here is the honest ledger.
| STIR/SHAKEN does | STIR/SHAKEN does not |
|---|---|
| Let the prospect's carrier verify that your number was not spoofed. | Show your company name, logo or reason for calling. That is branded caller ID and Rich Call Data. |
| Give carrier analytics one more input: the FCC notes providers may use attestation in their blocking and labeling tools. | Override a Spam Likely label. Labels come from analytics engines that weigh call patterns and complaints, not just attestation. |
| Sometimes trigger a verified indicator, such as a check mark, on the handset. | Ensure that indicator appears. The FCC notes it may show while ringing, only in the call log, or not at all, depending on the carrier and device. |
| Make it harder for scammers to impersonate your numbers over time. | Make your calls lawful. Consent, Do Not Call and calling-hour rules apply regardless of attestation. |
Why an A grade is no shield
The FCC's own numbers show why carriers cannot treat A as a trust signal on its own. In its 2026 proposal the Commission cites data that "48 percent of illegal calls are A-attested" and that 93.4% of robocall traffic from the most prolific robocall signers carries A attestations (Federal Register, July 2026). If bad actors get A grades too, analytics engines have to look at behavior, which is why your caller ID reputation matters more day to day than your attestation level.
Why a missing or low grade still hurts
The flip side is real. Robocall signing vendor TransNexus reports that in September 2026 robocalls made up 1.6% of A-attested calls, 4.6% of B-attested calls and 7.8% of C-attested calls in the traffic it sees (TransNexus, vendor data). Any analytics model trained on that pattern will treat B and C traffic with more suspicion. The same report found only 54.5% of calls arrived signed at all, so a large share of US traffic still reaches handsets with no attestation, much of it because of non-IP segments in the path.
Put together: getting A on your calls removes a reason to distrust them. It does not add a reason to answer. For the second half you need clean dialing behavior, registered numbers and possibly branded caller ID.
Which attestation your calls probably get
You rarely see the attestation on your own calls, but you can reason about it from how your dialer sources numbers. These are the common setups for outbound teams. Confirm the real answer with your provider, because the signing decision is theirs.
| Setup | Likely attestation | Why | What to do |
|---|---|---|---|
| Numbers bought inside your dialer or from its carrier | A, if the dialer's carrier signs with its own certificate | The signing provider issued the number to a known customer. | Ask who signs and with whose certificate. |
| Your own main line or toll-free number shown as caller ID through the dialer | B unless the provider has verified you control that number | The signer knows you but did not issue the number. | Ask whether they run a number verification step (letter of authorization or a callback test) that supports A. |
| Reseller dialer on top of a wholesale carrier | Depends on the upstream carrier's knowledge of the reseller and its customers | The FCC's 2024 rules make the provider with the obligation decide attestation and sign with its own certificate. | Ask which company's certificate signs the call. |
| Calls routed offshore before entering the US | C | The US entry point has no relationship with the caller. | Avoid for US prospecting. |
| Large pools of rotating local numbers | Can be A if each number is issued to you | Attestation is per call and per number, not per brand. | Fine for attestation, but read the reputation trade-offs before you rotate. |
The third row reflects a real change. Under the FCC's Eighth Report and Order, compliance with which was required by September 18, 2025, a provider with a signing obligation may let a third party do the technical signing only if it makes every attestation decision itself and signs with its own certificate, not the third party's (FCC DA 25-730). If your vendor answers "our partner handles that", ask whose certificate is on the call.
What to ask your dialer or carrier
You do not need to become a telecom engineer. You need five clear answers in writing. Send these as they are.
1. Which provider signs our outbound calls with STIR/SHAKEN, and is the signature made with that provider's own certificate?
2. What attestation level do our calls receive today, by number type (numbers you issued, numbers we brought, toll-free)?
3. If we display a number you did not issue, what verification do you need from us to give those calls an A attestation?
4. Does any of our traffic leave IP networks or route outside the US before it terminates?
5. Can you share a sample of call detail showing the attestation level on our recent calls?
Good answers name a specific carrier, say "A" for numbers they issued, describe a verification process for numbers you bring, and offer data. Weak answers are "we're fully compliant" with no detail. Compliance is the provider's obligation; what you need is the grade your calls actually receive.
Where the rules are heading (as of October 2026)
Several FCC proceedings could change how attestation affects your calls. None of the proposals below were final rules when this page was checked.
- Stricter attestation standards (proposed 2026). The FCC proposed codifying the A, B and C definitions, defining improper attestation, specifying how providers verify the number-to-customer link, and making the provider closest to the caller responsible for attestation (Federal Register, July 2026). Expect more verification paperwork from your provider.
- Verified caller names (proposed 2025). The Call Branding proposal would require terminating carriers that show an A-attestation indicator to also show a verified caller name, and would require originating providers to verify caller identity (FCC fact sheet, adopted as FCC 25-76). This is where STIR/SHAKEN and branded caller ID meet.
- Non-IP networks (proposed 2025). The FCC proposed requiring providers still on TDM to upgrade to IP or adopt a non-IP authentication framework (FCC). That would close one reason so many calls still arrive unsigned.
The direction is consistent: more verification of who the caller is, closer to the caller. Teams that already call from numbers they own, through a provider that knows them, will feel the least friction.
A short playbook for SDR leaders
- Get the five answers above from your dialer or carrier and keep them on file. Re-ask after any provider change.
- Call from numbers your signing provider issued or verified, so attestation is never the weak link.
- Register every outbound number with the analytics engines through the free registry covered in the Spam Likely guide, and watch caller ID reputation weekly.
- Stop wasting dials on dead numbers. Validate lists before they reach the dialer; see phone number validation.
- Decide on branding separately. If you need prospects to know who is calling before they pick up, evaluate branded caller ID on its own merits.
- Measure connect rate by number, not just by rep, so a number that starts underperforming is visible quickly. The connect rate hub covers the full set of fixes.
Frequently asked questions
Is my sales team required to implement STIR/SHAKEN?
No. The FCC's implementation obligation falls on voice service providers, gateway providers and certain intermediate providers, not on businesses that place calls. Your provider signs your calls. Your job is to choose a provider that signs with its own certificate and to call from numbers it can verify you control. This is not legal advice.
Will an A attestation stop my calls being labeled Spam Likely?
Not by itself. Spam labels come from carrier analytics engines that weigh call patterns, complaints and other signals, and attestation is only one input. The FCC cites data showing that 48 percent of illegal calls are A-attested, so carriers cannot rely on it alone. See the Spam Likely guide for remediation.
Does STIR/SHAKEN show my company name on the prospect's phone?
No. STIR/SHAKEN verifies the number, not the caller's name. Showing a verified name, logo or reason for calling requires Rich Call Data or a branded caller ID service. An FCC proposal from 2025 would link the two by requiring a verified name wherever an A-attestation indicator is shown.
What does the check mark or 'Verified' label on some calls mean?
It usually means the terminating carrier verified an A attestation on the call. Whether and where it appears depends on the carrier and the handset: the FCC notes it may show while ringing, during the call, only in the call log, or not at all.
Can I use local presence numbers and still get A attestation?
Yes, if each local number was issued to you by, or verified by, the provider that signs your calls. Attestation is about your right to use the number, not where it is located. Whether local presence is a good idea for reputation is a separate question covered in the caller ID reputation guide.
Why do so many calls still arrive with no attestation?
STIR/SHAKEN only works on IP networks, and parts of the US network still run on older TDM technology that can drop the signature. TransNexus vendor data put signed calls at 54.5% of terminating traffic in September 2026. The FCC has proposed rules to require non-IP authentication or an IP upgrade.
- 1.FCC, Combating Spoofed Robocalls with Caller ID Authentication
- 2.FCC, Call Branding FNPRM fact sheet: Improving Verification and Presentation of Caller Identification Information (2025)
- 3.FCC, FCC 25-76, Ninth Further Notice of Proposed Rulemaking (adopted October 28, 2025) (2025)
- 4.FCC Wireline Competition Bureau, DA 25-730: Effective date for STIR/SHAKEN third-party authentication rules (2025)
- 5.Federal Register (FCC), Enhancing Know-Your-Upstream-Provider Requirements and Strengthening STIR/SHAKEN Call Authentication (proposed rule) (2026)
- 6.FCC, FCC Proposes Action to Close the Non-IP Network Robocall Loophole (2025)
- 7.FCC, Caller ID Spoofing (2024)
- 8.TransNexus (vendor data), STIR/SHAKEN statistics from September 2026 (2026)
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