AssemblyAI vs Speechmatics: pricing, features and which to choose

AssemblyAI was founded in late 2017 by machine-learning engineer Dylan Fox after he found existing speech models inaccurate and difficult for developers to use. Its cloud platform serves product and engineering teams through APIs for recorded transcription, real-time speech, speech understanding, guardrails, voice agents, and language-model access. In December 2023, TechCrunch reported that AssemblyAI had raised $50 million in an Accel-led round, bringing total funding to $115 million. The company said its paying customer base had grown 200% year over year to 4,000 brands, while more than 200,000 developers used its platform. AssemblyAI also reported handling roughly 25 million API calls and more than 10 terabytes of data daily.

AssemblyAI’s workflow begins with choosing a product and model, then sending recorded audio through an HTTP request or opening a WebSocket for live transcription. For asynchronous files, developers select Universal-2 at $0.15 per audio hour or Universal-3.5 Pro at $0.21, add options such as speaker diarization, entity detection, or Medical Mode, and receive a transcript after processing. Streaming applications open a session, send audio frames, consume partial and final results, and send a termination message when finished because idle WebSocket time remains billable. Voice applications can connect to the Voice Agent API, provide a system prompt and tools, exchange audio in both directions, and handle turn detection and interruptions. Teams can then pass transcripts to Speech Understanding or the LLM Gateway for structured analysis.

AssemblyAI’s main limitations are cost complexity and developer overhead. Unlike Deepgram and Speechmatics, it bills streaming by open WebSocket duration, so idle time counts; add-ons, multichannel audio, and separate LLM Gateway token charges can also complicate forecasts. Google Cloud Speech-to-Text and AWS Transcribe may suit organizations already committed to those clouds, while AssemblyAI is a standalone API platform rather than a broader cloud suite. Its terms permit use of customer data to maintain, develop, and improve services, including model training, subject to applicable opt-out arrangements, so privacy reviews matter for sensitive workloads. AssemblyAI offers $50 in eligible credits, no monthly minimums, EU speech endpoints at US prices, and a $4.50-per-hour Voice Agent API. Choose it for API-first voice products needing transcription plus speech intelligence; choose competitors for cloud consolidation or simpler procurement.

Speechmatics grew out of research by Tony Robinson, who applied neural networks to speech recognition at Cambridge University in the 1980s, and the company was founded in Cambridge in 2006. Katy Wigdahl is chief executive. In 2022 it raised a $62 million Series B led by Susquehanna Growth Equity, according to TechCrunch. Its stated aim is to understand every voice, and its pitch rests on accuracy for accents, dialects and non-native speakers that trip up other engines. Customers range from broadcasters running live captions to contact centres, legal transcription firms and medical documentation companies. Speechmatics is one of the few speech vendors that has always sold on-premises and on-device deployment alongside its cloud API, which keeps it on shortlists for banks, governments and hospitals with strict data rules.

The product line now covers three jobs. Batch transcription processes recorded audio and video files, with speaker diarization, punctuation, custom dictionaries and translation. Real-time transcription streams live audio for captions and analytics. Agent STT, launched on September 17, 2026, is built for voice agents: it returns transcripts with turn detection, live speaker labels, speaker identification and up to 1,000 custom vocabulary terms over one connection. It plugs into the LiveKit and Pipecat agent frameworks, and Speechmatics says early users integrated it in under an hour. A text-to-speech API, added in June 2026, gives voice agents a matching output voice. Developers use REST and WebSocket APIs with SDKs, or a web portal for one-off files, and add-ons such as summaries and sentiment are priced separately.

Speechmatics' pricing is harder to read than Deepgram's or AssemblyAI's, because the published rates bundle discounts that depend on data sharing and annual commitments. Its text-to-speech is new and has a smaller voice range than ElevenLabs or Cartesia. Deepgram is the closest competitor for voice agents, with Flux turn detection at similar prices and a larger developer community. AssemblyAI is strong on audio intelligence features for recorded calls and meetings. OpenAI's transcription models are convenient for teams already on its API but offer no on-premises option. Pick Speechmatics for accented or code-switched speech, for medical transcription, for live broadcast captioning in many languages, or when audio must stay inside your own data centre. Benchmark it against Deepgram on your own recordings before signing a volume deal.