AssemblyAI

AssemblyAI offers speech-to-text and speech-understanding APIs built on its Universal model family, supporting async batch, real-time streaming, and a low-latency Sync API that returns a finished transcript from a single HTTP request in roughly 134 ms median. It supports 99+ languages and adds audio-intelligence features like speaker diarization, sentiment analysis, entity detection, and summarization, plus a Voice Agent API. Pricing is usage-based, starting around $0.15/hr for async transcription, with a free tier and enterprise plans. The company has raised over $115 million and is a leading developer-focused speech AI provider.

AssemblyAI builds speech AI models and exposes them through developer APIs for transcription and audio intelligence. Its Universal model family handles asynchronous batch transcription, real-time streaming, and a newer low-latency Sync API that returns a finished transcript from a single HTTP request in around 134 milliseconds at the median, without polling or WebSockets to manage. Beyond raw transcription, AssemblyAI offers audio intelligence add-ons such as speaker diarization, sentiment analysis, entity detection, and summarization, plus a Voice Agent API that bundles speech recognition, understanding, and response generation for building conversational voice applications. The models support 99+ languages, and pricing is usage-based with a free tier and enterprise plans. Backed by investors including Accel and Insight Partners with a $50 million Series C in late 2023 (over $115 million raised in total), AssemblyAI is a well-established, developer-focused option. It competes closely with Deepgram and Speechmatics, and tends to be chosen by teams that value model accuracy and a broad set of audio-understanding features.