Sierra launches fleming-1 to detect when a phone caller is an AI agent

A new question for the phone line

Sierra frames the launch with a comparison to Caller ID, which BellSouth introduced in Memphis, Tennessee in 1988. That technology answered the question of who was calling. Sierra says that 38 years later the question has changed to what is calling.

The company says it first met the issue last year, when agents built on Sierra started calling agents built on Sierra in healthcare. It now expects the problem to grow as personal agents such as Muse and Instinct take off. According to Sierra, a large share of the calls companies receive could come from AI acting on behalf of consumers.

How fleming-1 works

Sierra says it is becoming harder to tell a synthetic voice from a human one over the phone. Background noise, muffled audio and a bad connection can hide the clues, while AI voices keep improving.

fleming-1 analyzes a caller's speech in real time and scores the audio for signs that it was generated by AI. By looking beyond how a voice sounds to a human listener, the model helps teams assess whether the voice on the other end is synthetic while the call is still happening, according to Sierra.

Calls that fleming-1 identifies as likely AI are flagged. The company says the model is tuned to be conservative by default, so real people are not inadvertently flagged. fleming-1 works with any voice agent built on Sierra, and customers need to turn it on.

Information, not judgement

Sierra stresses that the model supplies information and does not dictate a response. As the company puts it, Caller ID never told you whether to pick up, and fleming-1 works the same way. Companies decide how to handle flagged calls.

The company points out that automated callers vary. Some will be fraudsters testing account security at scale. Others will be customers who handed a chore to an agent, or people who rely on text-to-speech. Its starting principle is that companies should know what is calling.

• A bank might add a verification step when the caller is an agent.
• A company with high call volume might start by measuring how often it happens.

Linked to Personal Agent Protocol

The launch follows Personal Agent Protocol, an open standard that Sierra says it is developing with industry partners. It gives personal agents a direct, authorized way to work with businesses. When an agent uses the protocol, the company knows it is an agent and who it is acting for. Sierra's blog lists Meta, Genesys, Instinct, Rocket, Shopify, Stripe and Walmart in connection with the standard.

Sierra acknowledges that some agents may not respect the protocol. In its words, the best case is an agent that says who it is, and for the calls where it does not, there is fleming-1.

What it means for businesses

For companies running voice agents on Sierra, the change is an option they can switch on to see which incoming calls are likely automated. Sierra argues that knowing when an agent is calling will become as accepted as Caller ID, which ended up on every phone because people found it useful. The source gives no pricing or accuracy figures for fleming-1.