STT / Speech-to-Text
Comparison of speech recognition solutions for conversational pipelines (2025–2026). Benchmarks, strategic stakes, and decision questions.
Strategic Framing — STT: Much More Than a WER
The Real Question
WER doesn't tell the whole story. The real question is: where is your voice data processed? Who has access to it? What is your strategy if the provider raises prices or gets acquired?
Infrastructure Spectrum
Cloud-only (Google, AssemblyAI) → Cloud+VPC (Deepgram, Azure) → On-premise (Azure containers, Inworld) → Self-hosted open-source (Whisper, Voxtral). Each step increases sovereignty and reduces lock-in.
2026 Market Signal
Deepgram ($1.3B) and AssemblyAI ($158M) are acquisition targets. Voxtral and Whisper are closing the quality gap. Inworld STT raised prices 400%+. The market is consolidating fast.
Questions to ask before choosing: Is your users' voice data subject to GDPR or Swiss nLPD? Do you need diarization or PII redaction? Does your architecture allow switching to a self-hosted model without major rework? What is your acceptable WER threshold for your specific domain?
Real-time cloud STT APIs — Deepgram Nova-3 is the latency reference (75ms TTFA). Whisper large-v3 is the open-source quality standard. AssemblyAI Universal-3 Pro leads the multilingual WER benchmark — Voice Agent API $4.50/hr (launched Apr 29, 2026).
Click a header to sort
| Solution | TTFA? | WER? | Streaming? | Multilingual | Diarization? | Price/hr | Sovereign? |
|---|---|---|---|---|---|---|---|
Deepgram Nova-3 Phase 1 MVP — ASR streaming | 75ms | 7.2% | ✓ | 36 langs | ✓ | $0.216/hr | ✓ |
Inworld STT Phase 1 MVP — STT émotionnel + Axe 2 Avatar Behavior | 92ms | 5% | ✓ | 100 langs | ✓ | $0.36/hr | ✗ |
AssemblyAI Universal-3 Pro Voice Agent Pipeline — Référence précision | 150ms | 4.9% | ✓ | 99 langs | ✓ | $0.372/hr | ✗ |
Azure Speech (Microsoft) Souveraineté suisse — institutionnel | 180ms | 5.9% | ✓ | 100 langs | ✓ | $1/hr | ✓ |
Google Speech-to-Text v2 Multilingue — option secondaire | 200ms | 2.7% | ✓ | 125 langs | ✓ | $0.36/hr | ✗ |
Deepgram Nova-3 is the industry reference for real-time voice agent ASR. 75ms P90 streaming latency, 36 languages, built-in VAD and endpointing. Voice Agent API at $4.50/hr provides a complete STT+LLM+TTS pipeline in a single WebSocket, with BYO LLM (GPT-4, Claude, Gemini) and function calling for RAG integration. No native voice cloning — Aura-2 TTS offers 36 preset voices; external TTS (ElevenLabs, Cartesia) can be integrated. On-premise deployment available for Enterprise (partial sovereignty). EU endpoint available. Used by Tavus, Simli, and most commercial avatar platforms.
Full details →Inworld STT (2025–2026) is the most feature-rich cloud STT API for interactive voice agents. Sub-100ms documented latency, 100+ languages via multi-provider routing (Whisper large-v3 + AssemblyAI). Unique real-time voice profiling extracts emotion (happy/calm/angry/frustrated), accent, age, pitch, and vocal style on every streaming chunk. Realtime API (full pipeline STT+LLM+TTS) from $0.015/min — 4x cheaper than OpenAI Realtime ($0.06/min). Native voice cloning: built-in + cloned + custom voices (up to 3,000 custom voices on Growth plan). RAG via function calling (tool calling mid-conversation). ZDR support. On-premise available on Enterprise. Drop-in compatible with OpenAI Realtime API.
Full details →AssemblyAI a lancé sa Voice Agent API le 29 avril 2026 : pipeline complet STT+LLM+TTS en une seule connexion WebSocket à $4.50/hr flat. Universal-3 Pro Streaming (u3-rt-pro) est le modèle STT temps réel, avec turn detection sémantique+acoustique, barge-in natif et session resumption. Tool calling (JSON Schema) permet d'intégrer un RAG custom (Pinecone, LlamaIndex, etc.) via function calling — pas de RAG natif mais intégration externe complète. Pas de clonage vocal natif : les voix disponibles sont prédéfinies (18+ voix EN/multilingual), mais il est possible d'intégrer un TTS externe (ElevenLabs, Cartesia) pour un clone vocal custom. LeMUR AI features (summarization, Q&A, sentiment) disponibles sur transcriptions. 99 langues, diarisation, timestamps mot-à-mot.
Full details →Azure Speech offers enterprise-grade STT with 100+ languages, custom model training, and Swiss data center (Zurich). 5.9% WER on English. Disconnected container deployment for partial sovereignty. Most expensive option but strongest enterprise compliance. Swiss German custom model available.
Full details →Google Speech-to-Text v2 avec Chirp 3 (GA mai 2026) : 2.7% WER EN (Artificial Analysis), 125+ langues, streaming gRPC bidirectionnel. MedASR open-source lancé fin 2025 (domaine médical). Expansion offline majeure (avril 2026). Pas de clonage vocal natif (via Google TTS séparé). RAG via tool calling + Vertex AI Search. Cloud uniquement, pas d'on-premise.
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