Speechmatics vs Deepgram vs AssemblyAI — Speech-to-Text APIs Compared

Speech-to-text is a commodity until it is not: the moment your users have accents, your calls have crosstalk, or your compliance team says audio cannot leave the building, the differences between providers become the whole decision.

Accuracy

On clean English audio all three are close and all publish word-error-rate claims that favour themselves. Speechmatics has built its reputation on accented and non-native speech and on languages the others cover thinly, and independent tests have often supported that on difficult audio. Deepgram and AssemblyAI both have strong models for English and the major languages. The only reliable answer is to run your own recordings through all three; accuracy is domain-specific.

Speed and voice agents

For real-time voice agents, streaming latency matters more than a point of accuracy, and Deepgram has led here, which is why many voice-agent platforms default to it. AssemblyAI's streaming has improved substantially, and Speechmatics offers real-time too, but Deepgram remains the common choice for latency-sensitive builds.

Deployment and compliance

• Speechmatics: cloud, on-prem, and container deployment, which regulated industries need
• Deepgram: cloud, with self-hosted options on enterprise plans
• AssemblyAI: cloud, with EU data residency options

Price

Deepgram is generally the cheapest per hour at scale. AssemblyAI is competitive and bundles intelligence features that would otherwise be a second model call. Speechmatics is priced higher, with the free monthly allowance as the entry point. For most products the transcription bill is small next to the language-model bill, so choose on accuracy and features first.

Bottom line

Deepgram for voice agents and cost. AssemblyAI for transcripts with built-in summaries and analysis. Speechmatics for accents, languages, and on-prem. Test with your own audio; the vendor benchmarks will not settle it.