AssemblyAI

AssemblyAI is a Voice AI infrastructure company that provides speech-to-text and speech-understanding APIs for developers building transcription, voice agent, and conversation-intelligence products. Rather than a single transcription endpoint, it offers a full platform: pre-recorded and real-time (streaming) speech-to-text, a Sync API for near-instant single-call transcription, a Voice Agent API for building production voice bots, a Speech Understanding API for extracting meaning from conversations, and Guardrails for redacting sensitive information before it reaches downstream systems or LLMs.

At the core of the platform is the Universal model family. Universal-3.5 Pro is AssemblyAI's most accurate model for pre-recorded audio, built to transcribe real-world conversations with native code switching across 18 languages and improved speaker diarization. Universal-2 offers strong accuracy at a lower price point across 99 languages for cost-sensitive use cases. On the real-time side, Universal-3.5 Pro Realtime adds context carryover and conversation memory for voice agents, while Universal-Streaming and its multilingual variant provide fast, production-ready transcription for English and five additional languages respectively. Beyond raw transcription, the Speech Understanding API and various add-ons extract speaker identity, sentiment, chapters, topics (via IAB taxonomy), entities, key phrases, and summaries from a single API call, while Guardrails handles PII redaction and content moderation inline.

AssemblyAI is built for developers and product teams at companies building call analytics platforms, AI notetakers, medical transcription tools, dictation apps, contact center agent-assist software, and conversational voice agents. Notable customers include Zoom, Fireflies, Granola, HeyGen, and Siro. Pricing is entirely pay-as-you-go with no concurrency limits or forced commitments, and new accounts get a generous free tier (185 hours of pre-recorded transcription, 333 hours of streaming) with no credit card required, making it accessible for prototyping before scaling into production.

AssemblyAI uses pay-as-you-go, hourly pricing with no minimum commitments or concurrency fees. Pre-recorded transcription: Universal-3.5 Pro costs $0.21/hr, Universal-2 costs $0.15/hr. Real-time streaming: Universal-3.5 Pro Realtime costs $0.45/hr, while Universal-Streaming and Universal-Streaming Multilingual cost $0.15/hr each. The Sync API (single-call, near-instant transcription) is $0.45/hr. The Voice Agent API is priced at $4.50/hr ($0.075/min), which includes speech-to-text, the Voice Agent LLM, text-to-speech, turn detection, interruption detection, recordings, and hosting infrastructure with no additional per-layer fees. Add-on features are billed separately per hour of audio processed: Speaker Diarization ($0.02\u2013$0.12/hr depending on model), Keyterms Prompting ($0.04\u2013$0.05/hr), Medical Mode ($0.15/hr), Translation ($0.06/hr), Entity Detection ($0.08/hr), Topic Detection ($0.15/hr), Content Moderation ($0.15/hr), PII Text Redaction ($0.08/hr), PII Audio Redaction ($0.05/hr), and several others priced between $0.01\u2013$0.08/hr. New accounts get a free tier with up to 185 hours of pre-recorded transcription and 333 hours of streaming transcription, no credit card required. Volume discounts and custom enterprise pricing are available by contacting sales.