How accurate is AssemblyAI's transcription?

AssemblyAI claims industry-leading accuracy with its Universal-3.5 Pro model, consistently topping benchmarks and supporting natural language prompting for customization.

Does AssemblyAI support real-time voice agents?

Yes, the Voice Agent API provides a managed speech-to-speech pipeline (STT -> LLM -> TTS) with end-to-end latency around one second, including turn detection and interruption handling.

Can I redact sensitive information from transcriptions?

Yes, the Guardrails API handles PII redaction and content moderation inline on both raw audio and transcripts before they reach your logs or LLMs.

What are the streaming client's key parameters for optimal performance?

For streaming, configure `speech_model` (e.g., 'universal-3-5-pro'), `sample_rate` (16000 Hz is standard), and `continuous_partials` for ongoing transcription updates.

How does the Speech Understanding API work with transcripts?

It's an additive layer; you send a transcript (or audio file) to the API, which returns structured analysis like sentiment, summarization, and topic detection without needing to build custom NLP pipelines.

What LLMs are available through the LLM Gateway?

The LLM Gateway provides unified access to models from providers like OpenAI (GPT), Anthropic (Claude), and Google (Gemini), along with community models, allowing fallback and model swapping from a single endpoint.

Directory/Audio Generation/AI APIs/AssemblyAI

AssemblyAI

AssemblyAI provides a complete Voice AI infrastructure platform. It offers state-of-the-art speech-to-text APIs for pre-recorded, streaming, and synchronous audio, with leading accuracy in 99 languages. Beyond transcription, it provides Speech Understanding APIs for analysis like summarization and sentiment, Guardrails for PII redaction and safety, and a unified LLM Gateway. The platform also includes a managed Voice Agent API for building real-time, speech-to-speech applications with built-in turn detection. It targets developers, founders, and product teams building voice-enabled products, from AI notetakers and call analytics to voice agents and medical transcription. It's designed for scalability from MVP to production.

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Added on

Sep 18, 2026

Speech-to-TextReal-time STTVoice AgentSpeech UnderstandingGuardrailsLLM Gateway99 LanguagesUniversal-3.5 Pro

Product information

Everything worth knowing about AssemblyAI

The complete picture — from everyday features to the technical detail builders and IT folks dig for.

Core features

What it actually does

Pre-recorded Speech-to-Text API

Transcribes recorded audio and video asynchronously across 99 languages, with support for speaker diarization, PII redaction, and more features. Built for teams processing recorded calls, podcasts, or meetings at scale.

Streaming Speech-to-Text API

Handles live audio over WebSocket with ~150ms p50 latency, powering voice agents, live captions, and real-time agent-assist tools in contact centers.

Voice Agent API

A fully managed speech-to-speech pipeline — one connection handles STT, LLM reasoning, and TTS together at roughly one second end-to-end latency, for teams that want AssemblyAI to own the whole voice-agent stack.

Speech Understanding API

Layers speech analysis on top of transcripts — summarization, sentiment, topic detection, and more — for extracting structured insight.

Guardrails API

Provides safety, privacy, and compliance controls — PII handling, content moderation, and related safeguards — for teams that need to govern what audio data flows through their pipeline.

LLM Gateway API

Gives unified access to frontier language models (GPT, Claude, Gemini, Community Models) through the same API, so teams can apply reasoning models to their transcription without a separate integration.

Dictation API

The first API built for dictation. Your users speak, and it returns text that is ready to send: filler gone, self-corrections resolved, names spelled right.

Must watch videos

AssemblyAI for AI Speech to Text API Honest Review - Watch Before Using

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Review2:23

AssemblyAI for AI Speech to Text API Honest Review - Watch Before Using

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AssemblyAI - Build AI applications with spoken data

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Tutorial1:02

AssemblyAI - Build AI applications with spoken data

Welcome to the AssemblyAI YouTube channel, where we cover the latest innovations in AI and how to build AI-powered features fast. At AssemblyAI, we are leveraging the latest AI research to continuously improve accuracy and offer production-ready Voice AI models — all with a developer-friendly API. We love to share what we know best. So on this channel, we bring you the latest developments in AI, tutorials, and educational videos on Machine Learning and Deep Learning. Every week, we'll be with you with fresh content. You can follow us on other social media too! - Follow us on X: https://www.x.com/AssemblyAI To see AssemblyAI in action, choose your favorite audio or video file and upload it into our no-code playground. Explore here: https://www.assemblyai.com/playground/?utm_source=youtube&utm_medium=referral&utm_campaign=yt_short_promo To see all the models we offer and start using them with a free API token visit our website: https://www.assemblyai.com/?utm_source=youtube&utm_medium=referral&utm_campaign=yt_short_promo

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Tutorial4:31

AssemblyAI Product Overview

AssemblyAI is building AI systems that help you build AI applications with spoken data. We create superhuman AI models for speech recognition, summarization, knowledge augmentation of language models with spoken data, and much more. Our platform enables product teams to integrate intelligent solutions into their products — fast — at an extremely large scale. And all of this is available through our simple API platform. Here are all the models that you can use through AssemblyAI’s API 00:00 Introduction 00:37 Speech Recognition Model 00:56 Speaker Diarization Model 01:05 Summarization Model 01:12 Auto-Chapters Model 01:20 Usecase: Podcast Platform 01:35 Content Moderation Model 01:53 Topic Detection Model 02:14 Usecase: Platfrom Safety 02:34 PII Redaction Model 02:50 Key Phrases Model 03:02 Sentiment Analysis Model 03:12 Entity Detection Model 03:23 Usecase: Contact Center Monitoring 03:40 LeMUR: A Framework for Applying LLMs to Spoken Data 04:13 Get Started with AssemblyAI Get Your Free AssemblyAI API Key - https://www.assemblyai.com/?utm_source=youtube&utm_medium=referral&utm_campaign=yt_po_2 AssemblyAI Playground - https://www.assemblyai.com/playground/?utm_source=youtube&utm_medium=referral&utm_campaign=yt_po_2 AssemblyAI LeMUR Playground - https://www.assemblyai.com/playground/v2/?utm_source=youtube&utm_medium=referral&utm_campaign=yt_po_2

Who uses it

Real use cases, no hype

Voice Agent Development

Build conversational AI agents with real-time speech-to-speech pipelines, turn detection, and interruption handling.

Call Analytics

Transcribe and analyze sales/support calls at scale for insights, sentiment, and coaching.

Medical Transcription

Convert patient conversations into accurate clinical notes with speaker diarization and PII redaction.

AI Notetakers & Meeting Summaries

Automatically transcribe meetings and generate summaries, action items, and key topics.

Live Captioning & Subtitling

Generate real-time, low-latency captions for live streams, broadcasts, and accessibility.

Agent Assist in Contact Centers

Provide real-time transcription and suggested responses to human agents during calls.

Dictation & Voice Input

Use the Dictation API for clean, ready-to-send text from raw speech, fixing filler words and self-corrections.

What's great

Industry-leading transcription accuracy with Universal-3.5 Pro
Massive language support (99 languages) for global applications
Real-time streaming with ~150ms latency for voice agents
Comprehensive platform (STT, Understanding, Voice Agents, Guardrails, LLM Gateway) in one
No concurrency limits or throttles; scales from MVP to 400k+ hours/month

Technical strengths

Unified API for both pre-recorded and real-time transcription
Built-in PII redaction and content moderation via Guardrails API
Managed Voice Agent API with turn detection and interruption handling
LLM Gateway provides unified access to frontier models (GPT, Claude, Gemini)

Where it falls short

Sync API limited to 120 seconds per request
Pricing details require clicking through to a separate page
Homepage is heavy on marketing, can feel overwhelming to navigate
Self-hosted option exists but primary focus is cloud platform

Technical limitations

Streaming WebSocket connection requires specific client implementation
Speech Understanding features (sentiment, chapters) are additive API calls
Dictation API is a specialized new product, not general-purpose STT

For technical folks

The deep-dive specs

FAQ

Includes technical Q&A

Pre-recorded is for async batch processing of long files, Realtime uses WebSockets for streaming with ~150ms latency, and Sync is a single HTTP request for short clips (≤120 seconds) with no polling.