Retell, the AI voice agent platform for contact centers, today launched Tell-1, a language model built specifically for live contact center calls that optimize for the high intelligence, low costs, and low latency needed. Trained on hundreds of millions of calls, Tell-1 is designed for the moments where AI voice agents most often fail: when a caller gives half an answer, changes the subject mid-task, or needs the agent to look something up and act, all while someone waits on the line.
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Retell vCX Voice AI Benchmark
General-purpose LLMs are built to handle an enormous range of complex tasks, from writing code to solving math problems. That breadth comes at a price: higher latency and higher cost. In a contact center, latency—the gap between when a caller stops speaking and when the AI agent starts replying—is what separates a natural conversation from a frustrating one. Cost matters just as much: an extra $0.05 to $0.10 per call adds up quickly across millions of calls a month.
Retell built Tell-1 to deliver the lowest possible latency and cost without sacrificing call quality. On Retell’s live benchmark, Tell-1 is currently responding in under 100 milliseconds, and it is built to stay under 300 milliseconds even at peak call volumes. Across the five measures that matter most on a live contact center call (instruction following, grounding, tool calling, colloquial quality, and latency), Tell-1 posted the highest overall score of any model tested, ahead of the latest models from OpenAI, Google, and Anthropic.
“Enterprises need to be able to trust voice AI agents with the calls that matter,” said Bing Wu, co-founder and CEO of Retell. “For AI voice agents, the bottleneck isn’t intelligence but timing: the model has to reason through the business’s rules and act in the time it takes a person to pause, and that’s the problem we built Tell-1 to solve.”
Tell-1 uses an interleaved reasoning architecture to allow the model to think while speaking. Rather than treating each turn as an isolated question, the model reasons through the conversation as it unfolds: which of the business’s rules apply now, which do not, what information is still missing, and whether to ask, respond or act. In practice, Tell-1 helps AI voice agents:
- Follow long, complex instructions: Keeping a business’s goals, policies and exceptions in view from the first minute of a call to the last.
- Work with partial answers: When a caller gives only a first name, the agent asks for the missing detail instead of guessing or restarting the form.
- Handle detours: The agent acknowledges an off-topic question, then returns to the task without sounding like the conversation has reset.
- Act at the right time: Calling the right tool, such as an availability or account lookup, once it has enough information and using the result to move the call forward.
Retell also today introduced Retell Dialer, the first dialer for voice agents to orchestrate outbound campaigns across AI voice and SMS agents. Where Tell-1 handles decisions during a live conversation, Dialer turns the outcome of that conversation into the next action.
A requested callback replaces the next planned attempt and resumes the same conversation at the contact’s requested local time; a qualified prospect moves to a specialist agent; and someone interested but not ready receives an SMS follow-up from a nurture agent. Retell Dialer also brings together contact screening, local presence and calling windows, number rotation and spam monitoring, configurable retries, and CRM integration.
Together, Tell-1 and Retell Dialer extend Retell’s voice-first platform, giving enterprises the intelligence to handle complex customer conversations and the orchestration to act on their outcomes. To learn more about Tell-1 and Retell Dialer, visit www.retellai.com.
About Retell
Retell is the AI voice agent platform for contact centers. Retell combines purpose-built voice technology with hands-on expertise to help enterprises launch quickly, while giving their teams the control to build, test and improve AI agents themselves. Founded in 2023, Retell serves more than 4,000 businesses, including Lenovo, CVS Health, and BILL, and handles more than 100M connected calls a month. Learn more at retellai.com.
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