AssemblyAI Review

AssemblyAI is a speech-to-text API, billed by the hour of audio rather than by seat or subscription, with a Voice Agent API that bundles speech recognition, an LLM and text-to-speech into one connection. What decides whether it suits you is whether pay-as-you-go usage pricing fits your volume better than a flat monthly plan, and whether you need the newest Universal-3.5 Pro model or the wider language coverage of Universal-2.

What is AssemblyAI?

AssemblyAI is a speech recognition API delivered as a hosted service, with a browser-based Playground and dashboard for testing calls. There is no desktop or mobile app; everything runs through the API. AssemblyAI also offers self-hosted deployment, running its models inside a customer's own environment.

What the AssemblyAI API does

The API covers both pre-recorded and streaming transcription. Pre-recorded transcription runs on the Universal-3.5 Pro or Universal-2 models; streaming runs on Universal-3.5 Pro Realtime or Universal-Streaming. Universal-2 covers 99 languages, while the newer Universal-3.5 Pro model covers a narrower set of 18.

Word-level timestamps come with transcription. Speaker diarization, keyterms prompting for custom vocabulary of up to 1,000 terms, and PII redaction across both text and audio are add-ons on top of the base rate. Transcripts can be returned as JSON, plain text, SRT or VTT.

Working with other people

AssemblyAI also sells a Voice Agent API that bundles speech-to-text, an LLM and text-to-speech into a single connection, billed at $4.50 an hour, or $0.075 a minute. Text-to-speech is only available this bundled way, not as its own standalone endpoint. Self-hosted deployment keeps audio inside a customer's own network boundary rather than AssemblyAI's cloud.

AssemblyAI pricing: what each plan gives

AssemblyAI has no ongoing free plan and no fixed monthly subscriptions; every account pays as it goes, by the hour of audio processed. Pre-recorded transcription costs $0.21 an hour on Universal-3.5 Pro or $0.15 an hour on Universal-2. Streaming costs $0.45 an hour on Universal-3.5 Pro Realtime and $0.15 an hour on Universal-Streaming. A custom-quoted Enterprise tier is also offered. New accounts get a one-time $50 signup credit, stated as covering up to 185 hours of pre-recorded transcription or up to 333 hours of streaming transcription; this is a starting credit, not a recurring free tier.

Privacy and support

Customers can opt out of model training account-wide; when opted out, audio and transcripts are never used to train or improve its models. AssemblyAI maintains a SOC 2 Type 2 report covering security, availability and confidentiality. It offers GDPR-compliant EU-region data residency at no premium, and its privacy policy sets out GDPR rights for users in the EU and UK. A HIPAA BAA is available, signable without a sales call and at no premium. Support runs through email, live chat, a help centre and a community channel.

Who AssemblyAI suits

AssemblyAI suits developers building transcription or voice features who want to pay only for the hours they use, and who need either broad language coverage or a fast, newer model depending on the job. Diarization, custom vocabulary and redaction as add-ons, with word timestamps included, cover most production transcription needs, and self-hosting suits teams that cannot send audio to a third-party cloud at all.

It suits less well anyone wanting a flat monthly bill or a genuinely free ongoing tier, since AssemblyAI has neither: the $50 signup credit is a one-time allowance, not a plan.

Frequently Asked Questions