What is STIR/SHAKEN and does it stop spoofed calls?
The problem it solves
Caller ID was designed with no verification: whatever number the originating system asserts is what your phone displays. Robocallers exploited this to impersonate local numbers, banks and agencies at scale.
How it works
STIR/SHAKEN (Secure Telephony Identity Revisited / Signature-based Handling of Asserted information using toKENs) has the originating carrier cryptographically sign each call with an attestation level: A (carrier knows the customer and their right to the number), B (knows the customer, not the number), or C (only knows where the call entered its network). Downstream carriers verify the signature and can flag or block failures. The FCC has required implementation in IP networks since June 2021.
What it doesn't do
It authenticates the number, not the intent — a scammer using a real number they control passes verification. It also degrades over non-IP legacy segments and international handoffs. That is why 'Caller Verified' checkmarks reduce but do not eliminate spoofing.
Sources
FAQ
My phone shows 'Caller Verified' — is the call safe?
It means the displayed number was not spoofed in transit. The caller can still be a fraudster using a number they legitimately control.
Why do I still get spoofed calls?
Legacy network segments, small non-compliant originators and overseas gateways still leak unsigned traffic; enforcement is ongoing.