STIR/SHAKEN Explained: Why Your Call Shows Spam Likely (2026)

If your phone shows “Spam Likely”, “Scam Likely” or “Potential Spam”on incoming calls — or if your own calls keep getting that label and people don't pick up — the system doing that labelling is called STIR/SHAKEN. It's a call-authentication framework mandated by the US Federal Communications Commission (FCC) since 2021 and expanded in April 2026 to cover gateway providers handling international traffic. Canada's CRTC has adopted the same framework; the UK and most of the rest of the world have not. This guide explains how STIR/SHAKEN actually works, what the attestation levels mean (A, B, C), why your call gets labelled, what you can do about it as a caller, and why VoIP calls from outside the US increasingly struggle to reach US recipients without “Spam Likely” treatment.

What “STIR/SHAKEN” Actually Stands For

Two acronyms describing two parts of the same framework:

• STIR = Secure Telephone Identity Revisited. An IETF protocol standard (RFC 8224 and related) that defines the cryptographic signatures used to authenticate caller identity. It's the “math” layer.
• SHAKEN = Signature-based Handling of Asserted information using toKENs. A framework developed by the ATIS / SIP Forum that defines how telephone carriers actually deploy STIR in their networks. It's the “plumbing” layer.

In practice, you'll see them written together as STIR/SHAKEN(or sometimes “SHAKEN/STIR”), and they're used interchangeably for the framework as a whole. The combined name is partly an industry joke about cocktail-making — James Bond's “shaken, not stirred” martini.

How a STIR/SHAKEN Call Works (Plain English)

When you make a call in a STIR/SHAKEN-enabled network, four things happen behind the scenes between you pressing call and the other phone ringing:

The Three Attestation Levels (A, B, C)

This is the part most consumers don't know exists but that determines how a call is treated by US/Canadian carriers. Every STIR/SHAKEN-signed call is assigned one of three attestation levels:

Why You See “Spam Likely” on Incoming Calls

The label is generated by your phone carrier (T-Mobile, AT&T, Verizon, Bell, Rogers, etc.) based on a combination of signals:

• STIR/SHAKEN attestation level— A passes cleanly; C is the highest risk; B sits in the middle.
• The carrier's own spam-scoring algorithm— takes into account call patterns, complaint history of the originating number, and machine- learning models trained on known robocall traffic.
• Third-party reputation feeds— services like First Orion, Hiya, RoboKiller and Truecaller share spam-number databases that influence labelling.
• User reports— calls reported as spam by enough users get flagged faster.

Each US carrier uses a slightly different spam-label algorithm and even slightly different language on the screen. T-Mobile and Sprint show “Scam Likely” as a label on the dial-out side. AT&T uses “Spam Risk”. Verizon uses “Potential Spam”. They're all the same underlying signal.

Why Your Outgoing Calls Show as Spam (And How to Fix It)

If your own calls keep getting labelled “Spam Likely” on recipients' phones — for example you're a small business owner whose customers keep ignoring your calls — the cause is almost always one of:

STIR/SHAKEN Around the World (2026)

The framework was developed primarily in the US through the FCC's implementation of the TRACED Act (Telephone Robocall Abuse Criminal Enforcement and Deterrence Act, signed December 2019). Major adoption status as of mid-2026:

How STIR/SHAKEN Affects International Callers

The April 2026 FCC expansion to gateway providers is the part that matters most for international calling. Before April 2026, calls originating outside the US arrived in the US with no STIR/SHAKEN signature at all — they were treated like unattested calls in general, with carriers applying their own spam-scoring. After April 2026, the US gateway provider (the carrier that handles inbound international traffic) is required to assign at least a C-level attestation, which often results in the call being labelled “Spam Likely”.

For a diaspora caller in Dubai trying to reach family in California, this means:

• Your call rings; sometimes it's labelled “Spam Likely” on arrival.
• Your relative may decline to pick up unless they recognise your number.
• The likelihood of labelling depends on the routing path — calls that go through major direct-route carriers fare better than calls through grey-market wholesale carriers.
• A verified outbound caller ID (showing your real number rather than “Unknown”) significantly reduces the chance of automatic labelling.

Common Misconceptions

How to Check Your Number's Spam Reputation

If you're concerned your business or personal number is being labelled, several services let you check the current spam-reputation status:

• Free Caller Registry— the industry-shared registry where businesses can register legitimate numbers. Most major spam-database providers consult this.
• Hiya / First Orion / RoboKiller / Truecaller— check each service's number-lookup tool to see if your number is flagged in their database.
• YouMail Robocall Index— aggregate data on robocall patterns; if your number appears here it's flagged across multiple databases.
• Your phone provider's portal— some business-tier providers expose the STIR/SHAKEN attestation level you're currently being assigned on outbound calls.

How BubblyPhone Handles STIR/SHAKEN

BubblyPhone calls to US/Canadian numbers transit through our wholesale carrier partners that maintain STIR/SHAKEN compliance. Outbound calls are signed with the appropriate attestation level based on the verified caller ID you've configured on your account. This is one reason why our calls typically reach the recipient's phone without “Spam Likely” labelling — in contrast to anonymous browser dialler services where the call arrives unattested and gets flagged. For non-US/Canadian destinations, STIR/SHAKEN doesn't apply (those countries haven't adopted the framework), so the question is moot.

Common Questions

Related Resources