Tool Introduction

Dylan Fox founded AssemblyAI and serves as its chief executive, and the company traces back to 2017. The staff is an interdisciplinary group of research leaders, scientists, and engineers focused on building and scaling state-of-the-art Voice AI that is accurate, capable, easy to use, and safe.

Operations run remote-first, with team members in 16 countries and offices in New York and San Francisco. Outside funding includes a $50 million Series C round raised to build superhuman Speech AI models.

Demo Available?

Yes. Self-serve signup gives $50 in free credits with no credit card, plus a no-code Playground; enterprise buyers use Contact sales for a custom quote.

Tool's Accuracy

Accuracy here means a low word error rate (WER) against a reference transcript, correct capture of high-value entities such as names, medical terms, and money, and correct speaker attribution in diarized output. The Universal model family does that work, with Universal-3.5 Pro named the flagship speech model across 18 languages and Universal-3.5 Pro Realtime handling streaming.

Pre-recorded WER: Universal-3.5 Pro averages 4.35% normalized WER across four datasets (synthetic medical, accented English from India, general speech, webinar speech) versus 5.24% to 17.39% for ten competitor systems run under the same protocol, including Mistral Voxtral Mini, OpenAI GPT-4o Transcribe, ElevenLabs Scribe V2, Gladia, Deepgram Nova-3, and Azure Batch.
Streaming WER: Universal-3.5 Pro Realtime averages 5.53%, against Deepgram Flux at 8.87%, Deepgram Nova 3 at 9.39%, Cartesia at 10.10%, and Deepgram Nova 3 Multi at 10.64%.
Missed entities: 5.38% on proper nouns, alphanumerics, emails, and addresses, the best of four compared systems.
Third-party Pipecat STT Benchmark: semantic WER of 1.62% and median time-to-complete-turn latency of 335ms. On that benchmark AssemblyAI is not the top scorer, since Azure STT (1.18%), Soniox (1.29%), and Deepgram Nova 3 (1.34%) post lower semantic WER, and the 335ms figure ranks 5th of 10 measured providers, with Deepgram Nova 3 fastest at 247ms.
Method: audio was evaluated with production model settings, no custom model tuning or prompt engineering; diarization is scored via cpWER on DiPCo, CALLHOME, NOTSOFAR, and AMI; multilingual and code-switching metrics use Common Voice, FLEURS, and VoxPopuli.

Aggregate Rating

3.7/5 stars (estimated from informal sources and limited reviews)

Detailed Overview

What AssemblyAI Does

Applications get spoken audio back as usable text and structured data. Files up to 5 GB or 10 hours go through the asynchronous API, while live calls stream word by word in roughly 300 milliseconds. Past the raw words, the Speech Understanding API returns summaries, sentiment, and topics, and the Voice Agent API handles listening, model routing, and voice output over a single connection.

Who AssemblyAI Is For

Product and engineering teams that need speech inside their app without running speech infrastructure in-house are the core audience, from early-stage startups to Fortune 500s, with 200K+ developers building on voice data. Typical builders include contact-center and call-tracking vendors, meeting notetakers, sales-coaching and conversation-intelligence tools, medical scribe startups, video editors, and anyone shipping real-time voice agents.

Top Differentiators

Voice Agent pricing is flat at $4.50/hr against $18.00/hr for OpenAI's Realtime API, and the API surface stays small at roughly 6 event types versus 30+. A 30-second session-resumption window lets a dropped WebSocket reconnect, something the published comparison shows neither OpenAI nor Deepgram matching. On transcription, Universal-3.5 Pro targets names, phone numbers, and order IDs; the lower-cost Universal-2 covers 99 languages.

Founding Year

2017

Target Industry

B2B, Enterprise, Startups, Contact Centers, Conversation Intelligence, Voice Agents, AI Notetakers, Medical Transcription, Sales and Revenue Intelligence, EdTech, Brand and Media Monitoring, Captioning, Content Repurposing, Compliance Monitoring, Dictation, Transcription Services

Available Integrations

LiveKit: official voice-agent orchestration on Universal 3.5 Pro Realtime; prompting is a beta feature and context carryover needs livekit-agents 1.6.6+.
Pipecat: official integration with the open-source voice-agent framework, also built around the Universal 3.5 Pro Realtime model for conversational agents.
Twilio: official telephony integration for streaming live-call transcription and processing recorded voice messages, with sample code in Python, Node.js, C#, and Go.
Zapier: five actions (Transcribe, Get Transcript, Get Subtitles, Get Sentences, Get Paragraphs) across 5000+ apps; test mode returns transcripts early, so validate with a live Zap.
Make: official no-code integration for complex, branching automation scenarios built in Make's visual workflow builder.
n8n: built and maintained by AssemblyAI and verified by n8n, reaching over 1,000 apps; public Google Drive files must be 100MB or smaller.
Recall.ai: third-party meeting bot streaming Zoom audio for real-time transcription by webhook; AssemblyAI must be configured separately inside the Recall.ai dashboard.
Zoom RTMS: pulls Real-Time Media Streams directly from Zoom meetings into AssemblyAI for live transcription.
Amazon Connect and Genesys Cloud: contact-center integrations that build a transcription pipeline out of call-center recordings for enterprise telephony teams.
Telnyx: telephony integration documented for voice-agent development in combination with either Pipecat or LiveKit.
LangChain: AssemblyAI-maintained Python and JavaScript integration that transcribes audio so LangChain chains can operate on the resulting text.
MCP Server: wires the API into Claude Code, Cursor, or any Model Context Protocol (MCP) compatible coding agent.

AssemblyAI publishes no named subscription tiers. Pricing is a free signup plus pay-as-you-go usage, with a custom enterprise tier reached through the contact sales flow.

Free

Signup grants $50 in free credits with no credit card required, which the FAQ puts at up to 185 hours of pre-recorded transcription and up to 333 hours of streaming transcription. Free accounts are capped at 5 new streams per minute.

Pay-as-you-go

No minimum commitment, billed per unit of usage, with no stated cancellation penalty.

Pre-recorded speech-to-text: Universal-3.5 Pro $0.21/hr, Universal-2 $0.15/hr.
Realtime streaming: Universal-3.5 Pro Realtime $0.45/hr, Universal-Streaming English $0.15/hr, Universal-Streaming Multilingual $0.15/hr, with paid concurrency of 100 new streams per minute.
Sync Speech-to-Text API: $0.45/hr, single call, up to 2 minutes per request, with ~134ms p50 latency.
Voice Agent API: $4.50/hr ($0.075/min), billed per second of connected conversation time and inclusive of speech-to-text, the Voice Agent LLM, text-to-speech, turn detection, interruption detection, hosting and orchestration, and Twilio SIP trunking, with no per-layer add-ons, concurrency fees, or per-agent subscriptions.
Transcription add-ons: Medical Mode +$0.15/hr on all models; Speaker Diarization +$0.02/hr async or +$0.12/hr streaming; Keyterms Prompting +$0.05/hr on Universal-3.5 Pro, included on Universal-2 async and Universal-3.5 Pro Realtime, +$0.04/hr on Universal-Streaming; free-text Prompting +$0.05/hr on Universal-3.5 Pro only; Voice Focus +$0.10/hr on Universal-3.5 Pro Realtime.
Guardrails: PII Text Redaction +$0.12/hr streaming or +$0.08/hr as a Guardrails add-on, PII Audio Redaction +$0.05/hr, Content Moderation +$0.15/hr, Profanity Filtering +$0.01/hr.
Speech Understanding, per hour of audio: Speaker Identification $0.02/hr low effort or $0.10/hr medium effort, Translation $0.06/hr, Custom Formatting $0.03/hr, Entity Detection $0.08/hr, Sentiment Analysis $0.02/hr, Key Phrases $0.01/hr, Topic Detection $0.15/hr, Summarization $0.02/hr low effort or $0.07/hr medium effort.
LLM Gateway: billed per 1 million tokens with input and output priced separately across 34 models labeled Bedrock, Vertex, OpenAI, and AssemblyAI, ranging from GPT-5 Nano at $0.05/1M input and $0.40/1M output up to Opus-tier models at $5.00/1M input and $25.00-$30.00/1M output. Listed rates are for global routing, set with the model_region: global parameter; in-region US or EU pricing is 10% higher.

Custom / Enterprise

Reached through the Contact us option, covering custom rate limits, enhanced concurrency, and enterprise flexibility for speech-to-text and the LLM Gateway. Voice Agent API buyers additionally get volume discounts, a dedicated Forward Deployed Engineer to take the build live, and custom voices tailored to the brand. No price is published for this tier.

Billing mechanics

Pre-recorded transcription is billed per audio hour submitted, with multichannel audio billed per channel. Streaming is billed on connection duration rather than audio actually sent, so idle connection time counts. HIPAA BAA, PCI-DSS, ISO 27001, and SOC 2 are included at no premium.

Pricing last verified: 09/09/2026
Disclaimer: Pricing is subject to change. Please confirm current pricing on the vendor site.

Features & Specs

Pre-recorded API: files up to 5 GB per request (2.2 GB for local uploads), 160 milliseconds to 10 hours, with per-word confidence scores.
Universal-3.5 Pro: $0.21/hr in 18 languages, falling back to Universal-2 when a language is unsupported.
Universal-2: $0.15/hr in 99 languages, with per-language word error rate (WER) bands from high (10% or less) to fair (over 50%).
Streaming: Universal-3.5 Pro Realtime, $0.45/hr, sub-300ms latency in 18 languages; Universal-Streaming English and Multilingual (6 languages), $0.15/hr.
Sync API: one call returns a finished transcript for clips up to 120 seconds.
Voice Agent API: flat $4.50/hr ($0.075/min) covering speech-to-text, LLM routing, voice generation, turn detection, interruption handling, and tool calling via JSON Schema.
Speech understanding: summarization, sentiment analysis, topic detection, entity detection, key phrases, auto chapters, speaker diarization, code switching, multichannel audio.
Guardrails: personally identifiable information (PII) redaction, profanity filtering, and content-safety controls, from +$0.05/hr to +$0.08/hr.
Medical Mode: the medical-v1 domain, +$0.15/hr, covers medications, procedures, and dosages in English, Spanish, German, and French.
LLM Gateway: per-token access to OpenAI, Anthropic, Google, and Alibaba Qwen models.
Developer tooling: Python and TypeScript SDKs, a no-code Playground, $50 in signup credits, and EU processing priced like the US region.

Security & Compliance

Audits: a SOC 2 Type 2 report covering security, availability, and confidentiality, audited annually by an independent firm, plus annual third-party penetration testing and regular vulnerability scans.
Included at no premium: HIPAA BAA, PCI-DSS certification for the Voice Agent API, ISO 27001, SOC 2 Type 2, and GDPR compliance, with EU-region processing priced the same as the US region.
Encryption: TLS 1.2+ for data in transit and AES-256 for data at rest across all environments.
Data retention: audio and transcripts are retained only as long as needed for processing, and a Zero Data Retention account-level setting means files and transcripts are never stored after processing completes.
Access control: role-based access control and least-privilege permissions for production systems, with Single Sign-On (SSO) offered.
Model training: customers can opt out of model training at any time, after which audio and transcripts are never used to train or improve the models, and the opt-out applies across all AssemblyAI APIs.
Monitoring and evidence: centralized logging and monitoring with documented incident-response procedures, and compliance evidence published through a Trust Center hosted on Vanta.

Industry Use-Cases

Sales Coaching

Siro records field sales conversations, and coaching is only trusted when the transcript underneath it is right. Routing that audio through AssemblyAI, per the company's published case studies, reduced customer complaints and support tickets by 90%.

Contact Centers

Every conversation has to be transcribed across markets before a contact-center platform can score or route anything. Calabrio moved that layer onto AssemblyAI, which boosted customer satisfaction by 80% and accelerated global expansion.

AI Meeting Notetakers

Meeting notes are worth paying for only when the underlying transcript holds up. Supernormal rebuilt its notetaker on AssemblyAI, and its chief executive states the free to paid conversion rate doubled. Grain, working the same market, increased customer satisfaction by 12%.

Customer Research

Dovetail turns interviews and support calls into continuous customer intelligence, so a garbled transcript quietly corrupts every theme built on top of it. Adopting AssemblyAI improved word error rate by 36%.

Real-Time Voice Agents

Super runs voice agents for real estate, where each live call burns streaming transcription by the minute. Scaling those agents on AssemblyAI delivered 30% cost savings on real-time transcription and an 80% increase in customer satisfaction.

Call Tracking

Attribution products live or die on transcribing high call volume cheaply. WhatConverts achieves over 50% cost savings on that workload, while Earmark reports an 83% cost reduction with unlimited scalability.

Media Localization

Subtitling and localization start with a hand-checked transcript in each language, which is where Ollang spent its hours. Integrating Voice AI stripped out 76% of the manual processing.

Tool's Alternatives

Deepgram: bundles speech-to-text, text-to-speech, and LLM orchestration behind one Voice Agent API call, positioned as a way to cut complexity, latency, and cost versus stitching separate vendors together, with newer Flux models built for turn-taking and interruptions in live conversation. Those conversational strengths sit in the Flux line rather than uniformly across the catalog. Single-vendor coverage of the whole voice-agent stack is the differentiator, where AssemblyAI centers on transcription and understanding and applies LLMs through its Gateway.

Speechmatics: independent Pipecat testing recorded a 1.07% pooled word error rate, the lowest of the 12 services benchmarked and ahead of Deepgram, AWS, and Azure, paired with 55+ languages and mid-sentence code-switching. The accuracy claim rests on that single third-party benchmark rather than a disclosed in-house methodology. Deployment sets it apart: on device, on prem, and in the cloud, which matters in regulated or air-gapped environments that a cloud-only API cannot serve.

Gladia: the Solaria-3 model reaches 100+ languages with accent-sensitive auto-detection and code-switching, reporting 9.6% WER on real English audio and diarization errors 3x lower than competing providers. Those numbers are self-reported rather than drawn from a disclosed independent benchmark. Diarization, translation, and entity detection come bundled into the base transcription call at no extra cost, alongside a stated sub-4-hour average integration time and native Pipecat, LiveKit, and Twilio support.

Rev: the rev.ai developer API chases the same build-transcription-into-your-product audience, with proprietary recognition stated as 47% more accurate than competitors in challenging environments and data that is neither sold nor used to train third-party AI models. Homepage messaging now leans toward the legal and investigative platform, leaving the pure developer API less prominently documented. Professional human transcriptionists and certified court reporters back a hybrid, guaranteed-accuracy path that a machine-only API does not offer.

Frequently Asked Questions

How much does AssemblyAI transcription cost per hour?

Pre-recorded transcription runs $0.21/hr on Universal-3.5 Pro and $0.15/hr on Universal-2. Streaming costs $0.45/hr for Universal-3.5 Pro Realtime and $0.15/hr for Universal-Streaming, billed pay-as-you-go with no minimum commitment.

Does AssemblyAI have a free tier for testing?

Signup includes $50 in free credits with no credit card required, enough for up to 185 hours of pre-recorded transcription or 333 hours of streaming, capped at 5 new streams per minute.

How many languages do AssemblyAI models support?

Universal-3.5 Pro covers 18 languages and Universal-2 covers 99. The Voice Agent API supports 6: English, Spanish, French, German, Italian, and Portuguese, with the same accuracy across all six.

Is AssemblyAI HIPAA and SOC 2 compliant?

HIPAA BAA, PCI-DSS for the Voice Agent API, ISO 27001, SOC 2 Type 2, and GDPR compliance are included at no premium, with EU-region processing priced the same as the US region.

How accurate is AssemblyAI against other providers?

On the published benchmarks, Universal-3.5 Pro averages 4.35% word error rate versus 5.24% to 17.39% for ten competitor systems, while the streaming model averages 5.53% with a 5.38% missed-entity rate.

What does the Voice Agent API price include?

A flat $4.50/hr ($0.075/min) covers speech-to-text, the Voice Agent LLM, text-to-speech, turn detection, interruption detection, hosting, and Twilio SIP trunking, with no per-layer add-ons or per-agent subscriptions.

Can customers opt out of model training?

Opting out of model training is available at any time and applies across all AssemblyAI APIs. A Zero Data Retention setting also stops audio and transcripts from being stored once processing completes.

How do developers integrate AssemblyAI into existing stacks?

Official Python and TypeScript SDKs sit alongside documented integrations for LiveKit, Pipecat, Twilio, Zapier, Make, and n8n, plus an MCP server for coding agents and a no-code Playground for first tests.

Which add-ons cost extra on top of transcription?

Medical Mode adds $0.15/hr, speaker diarization $0.02/hr async or $0.12/hr streaming, topic detection $0.15/hr, entity detection $0.08/hr, sentiment analysis $0.02/hr, and summarization $0.02/hr at low effort.

Comments are closed.

AssemblyAI

Voice AI infrastructure for developers building on speech