Glossary · AI & Agents
AssemblyAI
Overview
What AssemblyAI is
AssemblyAI is a speech-to-text (also called ASR, automatic speech recognition) API that converts spoken audio into written text. It serves two modes: asynchronous transcription of recorded files, and real-time streaming transcription for live audio such as phone calls.
Beyond raw transcription, it offers audio-intelligence features, including speaker diarization, summarization, sentiment analysis, and content moderation. It competes with providers like Deepgram and with self-hosted models such as OpenAI's Whisper.
How AssemblyAI works
For recorded audio, you upload or reference a file and receive a transcript with word-level timestamps and any requested intelligence outputs. For live audio, you stream chunks over a WebSocket connection and receive incremental transcripts as the caller speaks, which is what voice agents need to react in near real time.
AssemblyAI has released streaming models built specifically for voice agents, emphasizing low latency, intelligent endpointing (detecting when a speaker has finished), and keyword prompting to bias recognition toward domain terms. Exact model names and pricing change over time, so confirm current options in its documentation.
Where it fits in a voice-AI stack
AssemblyAI is the listening layer of a voice pipeline: it turns the caller's speech into text that a language model can reason over, before a text-to-speech engine speaks the reply. In an orchestrated stack with LiveKit, Pipecat, or Vapi, it is one interchangeable choice for the STT component.
Pick it when transcription accuracy, streaming latency, and built-in audio intelligence matter, and compare it against Deepgram, Whisper, and the transcription built into speech-to-speech models like the OpenAI Realtime API.
Where we use it
Related Zen in Tech services
How our team puts AssemblyAI to work in real projects.
FAQ
AssemblyAI — common questions
What is AssemblyAI used for?
AssemblyAI is used to transcribe audio into text and extract insights from it. Common uses include captioning recordings, powering voice agents with live transcription, and analyzing calls for topics, sentiment, and speakers.
Does AssemblyAI support real-time transcription?
Yes. AssemblyAI offers streaming speech-to-text over WebSocket with low latency and intelligent endpointing, which is designed for voice agents and other live applications that must respond while the speaker is still talking.
How does AssemblyAI compare to Whisper?
AssemblyAI is a managed API with streaming and audio-intelligence features, while Whisper is an open-source model you can self-host or call via OpenAI's API. AssemblyAI reduces infrastructure work; Whisper offers more control and self-hosting options.
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