AssemblyAI is the voice AI infrastructure platform that developers trust for building production-grade speech and audio intelligence into their applications. The platform offers a comprehensive suite of speech-to-text models including the flagship Universal-3 Pro for highest accuracy pre-recorded transcription and Universal-3 Pro Streaming for real-time use cases, with support for 99 languages. Beyond transcription, AssemblyAI provides a complete Speech Understanding layer that includes speaker identification, sentiment analysis, auto chapters, summarization, topic detection, key phrase extraction, and translation, all accessible through unified APIs. The Voice Agent API allows developers to build natural conversational AI experiences with built-in turn detection, while the LLM Gateway lets teams route audio transcripts through any major frontier model including GPT-5.5 and Claude 4.6 Sonnet without managing separate integrations. Enterprise-grade Guardrails handle PII redaction, profanity filtering, and content moderation to meet compliance requirements. The platform processes over 2 million hours of audio daily and powers voice features at Zoom, Runway, Supernormal, Jiminny, and hundreds of other companies across conversation intelligence, medical transcription, contact centers, and AI note-taking. With generous free tier credits, transparent pay-as-you-go pricing starting at $0.15 per hour, and custom enterprise plans, AssemblyAI serves solo developers prototyping voice features all the way up to large platforms running production voice agents at scale.