High-Accuracy Pre-recorded Speech-to-Text API

The platform offers two primary async models: Universal-3.5 Pro and Universal-2. Universal-3.5 Pro is positioned as the most accurate model, supporting 18 languages with native code switching and improved speaker diarization. Universal-2 offers a cost-effective alternative with support for 99 languages.

Business outcome: Delivers clean, customisable transcripts for a wide range of audio types, enabling accurate data analysis, search, and content repurposing.

Streaming Speech-to-Text API for Live Applications

For use cases requiring immediate feedback, the Realtime API streams transcripts with what the company describes as 'async-level accuracy'. This is crucial for voice agents and live captioning where response speed is critical.

Business outcome: Enables the creation of responsive voice agents and live transcription features that function without noticeable lag.

Production-Ready Voice Agent API

The Voice Agent API is designed to handle the complexity of building conversational agents, including turn detection and interruption handling. It is priced at $4.50/hr and includes the core speech-to-text, an LLM, text-to-speech, and the hosting infrastructure over a single WebSocket.

Business outcome: Significantly reduces the engineering effort required to deploy and manage voice agents, allowing teams to ship faster.

Speech Understanding API for Deeper Insights

This API goes beyond transcription to extract speaker ID, sentiment, chapters, and summaries from a single call. This provides a richer dataset for analysis without needing to build separate models.

Business outcome: Provides a more complete picture of customer conversations, enabling better insights for sales, support, and product teams.

Inline PII Redaction and Content Moderation

The Guardrails feature allows for the redaction of personally identifiable information (PII) and content moderation directly on audio and transcripts. This ensures sensitive data is handled securely and doesn't end up in logs or downstream LLMs.

Business outcome: Helps businesses meet compliance requirements and mitigate risk by preventing sensitive data leakage.

Unified Interface for Multiple LLMs

The LLM Gateway provides a single endpoint to route between various LLMs, including GPT, Claude, and Gemini, with built-in fallback mechanisms. This allows for model swapping and resilience against outages without code changes.

Business outcome: Provides flexibility and reduces the risk of vendor lock-in, ensuring application reliability and cost optimisation.

• Model AccuracyThe Universal-3.5 Pro model is positioned as a leader in accuracy, which is critical for applications where transcription errors are costly.
• Full-Stack PlatformOffers a comprehensive suite of APIs from transcription to voice agents, reducing the need to integrate multiple vendors.
• ScalabilityThe platform is built to handle significant scale, with no concurrency limits on the pay-as-you-go plan and infrastructure processing millions of hours daily.
• Developer ExperienceClear documentation, a no-code playground, and code samples make it straightforward for development teams to get started.

• Not a Turnkey SolutionRequires development resources to build the final application; it is an API, not a ready-to-use app.
• Usage Costs Add UpWhile the free tier is generous, costs can scale quickly with high volumes of audio, especially when using the top-tier models.
• Complex Pricing StructurePricing is per-hour and varies by model and feature (e.g., Voice Agent API), requiring careful cost modelling for large projects.
• Professional RealityBusinesses without in-house development capability will need to budget for engineering time to build and maintain the application layer around these APIs.

Customer Support Analytics

Transcribe support calls to analyse sentiment, identify common issues, and coach agents. The Speech Understanding API can extract summaries and chapters, turning raw calls into actionable business intelligence for support and product teams.

Real-time Voice Agents

Build and deploy conversational voice agents for sales, scheduling, or customer service. The Voice Agent API handles the complexities of real-time interaction, allowing developers to focus on the conversational logic and business rules.

Media Captioning & Repurposing

Generate accurate captions for video content in 99 languages to improve accessibility and SEO. The pre-recorded API can also be used to create transcripts for repurposing long-form content into articles or social media posts.

Compliance & Security Monitoring

Use the Guardrails feature to automatically redact PII from recorded conversations, ensuring compliance with data privacy regulations. This is critical for industries like finance and healthcare where sensitive information is routinely discussed.

Sign up for a free AssemblyAI account to get your API key and access the free tier credits.

Use the no-code Playground to upload a sample audio file and test the accuracy of the different transcription models.

Review the API documentation and integrate the Speech-to-Text API into your development environment using one of the provided SDKs.

Start with a small test project to process your own audio files and evaluate the output before scaling to production volumes.