# Assemblyai

> Speech AI platform: Universal STT models (promptable Universal-3 Pro), a flat-rate Voice Agent API, and speech understanding — summarization, sentiment, PII redaction.

AssemblyAI packages speech intelligence as one API: the Universal STT family — topped by Universal-3 Pro (February 2026), a promptable speech model you steer with natural-language context and keyterms — streaming for voice agents, a flat-rate Voice Agent API bundling STT+LLM+TTS over one WebSocket, and understanding layers. Freemium with signup credits, then per-hour usage.

Website: https://www.assemblyai.com

AssemblyAI's bet is that transcription is the *floor*, not the product: the value sits in **speech understanding** — and increasingly in owning the whole voice-agent loop. Its 2026 lineup runs from promptable STT to a one-WebSocket agent pipeline.

## Highlights

- **Universal-3 Pro** (Feb 2026) — promptable STT: steer with natural-language context and keyterms, capture disfluencies, handle code-switching; six native languages with routing to 99+.
- **Streaming STT** — the realtime tier voice agents and live captions build on.
- **Voice Agent API** (Apr 2026) — STT + LLM + TTS + turn detection + interruptions + tool calling over one WebSocket, flat-rate per hour.
- **Speech understanding** — summarization, sentiment, entities, topics, speaker labels/identification, translation across 89 languages.
- **Guardrails** — PII redaction, profanity filtering, and moderation in 50+ languages: the compliance layer audio pipelines need.
- **LLM Gateway** — route understanding workloads across GPT/Claude/Gemini with caching, keeping the audio and reasoning bills in one place.

## In an AI-assisted workflow

Sign up, take the key, POST files or open a WebSocket — Python/JS SDKs cover both. In [voice-agent stacks](/guides/voice/build-a-voice-agent) it's either the best-in-class STT component or, via the Voice Agent API, the whole pipeline; in data work, it's the "turn 10,000 calls into queryable, redacted, summarized records" machine.

> [!WARNING]
> Two billing edges: streaming meters **session time** (close idle connections), and the legacy best/nano model tiers are deprecated — new integrations should target the Universal family.

## Good to know

Hosted and proprietary, with a genuinely useful free-credit start. Against the field: [Deepgram](/tools/deepgram) competes hardest on enterprise streaming, [Whisper](/tools/whisper) is the self-host baseline, [Cartesia Ink](/tools/cartesia) the latency-first newcomer — the decision table is [Best Speech-to-Text APIs in 2026](/guides/voice/best-stt-apis-2026).

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_Source: https://agentscamp.com/tools/assemblyai — Tool on AgentsCamp._