AssemblyAI for Voice AI: Speech Capabilities, APIs, Integrations & Implementation
AssemblyAI is a speech-component platform offering production-ready realtime WebSocket STT, pre-recorded and sync transcription, speech-understanding modules, a Voice Agent API (audio return), SDKs and webhooks. Telephony/PSTN functions are expected to be provided by orchestration/telephony partners and integrated via standard audio transport.
Peak Demand evaluates the platform in the context of telephony, APIs, business rules, integrations, QA, monitoring, and the operating environment around the agent.
Discuss a AssemblyAI DeploymentWhat Is AssemblyAI?
AssemblyAI is a speech-component (STT/audio-intelligence) platform: production-ready realtime WebSocket streaming, pre-recorded and sync STT, speech-understanding (entities, summarization, diarization), a Voice Agent API that can return audio, SDKs (Python/JS) and webhooks. Native PSTN phone-number provisioning, SIP trunking and call routing are not documented in the reviewed official sources and are typically integrated via external telephony/RTC partners.
AssemblyAI Platform Profile
AssemblyAI
Speech component • STT/audio intelligence
Where AssemblyAI Fits in a Voice AI Technology Stack
Strong component fit for systems that supply or orchestrate audio transport (RTC or PSTN via partners). Use AssemblyAI for low-latency streaming STT, realtime voice agents, post-call analytics pipelines, and multilingual transcription — combine with an external telephony/RTC layer (LiveKit, Pipecat, or a telco SIP trunk) to handle PSTN origination/termination.
A Typical AssemblyAI Production Architecture
The exact architecture depends on the business environment, but Peak Demand evaluates the platform as one layer inside a connected production system.
AssemblyAISpeech component / STT / audio intelligenceAssemblyAI Capabilities Relevant to Production Voice AI
| Capability | Current position | Scope | Implementation context |
|---|---|---|---|
| Inbound calling | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Outbound calling | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Telephony / phone routing | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| SIP / trunking | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Webhooks / callbacks | Established | Product-native | Supports webhooks for pre-recorded transcripts and streaming sessions (webhook_url, optional auth headers). Streaming webhooks deliver finalized transcript after session terminates; pre-recorded transcription supports webhook callbacks. |
| Public APIs | Established | Product-native | Full Public API reference across Pre-recorded STT, Realtime (streaming) STT, Sync STT, Voice Agent API, Speech Understanding, and LLM Gateway. |
| SDKs / developer libraries | Established | Product-native | Official Python and JavaScript SDKs with examples for Pre-recorded, Realtime streaming, Sync, Voice Agent API and file upload flows. |
| Tool / function calls | Established | Platform-family | LLM Gateway and Voice Agent API provide LLM-managed flows; Streaming WebSocket messages include LLMGatewayResponse for integrated LLM responses. These are platform-level primitives for invoking/mediating LLMs in call flows. |
| Transfers / forwarding / handoff | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Conference / queue primitives | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Appointment booking | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Calendar integration | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Knowledge bases / retrieval | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Workflow automation | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Integrations / connectors | Established | Platform-family | Platform documents explicit integrations and guides for LiveKit, Pipecat and mentions common orchestration patterns; SDKs and webhooks provided to integrate with external systems. |
| Call recording | Limited / conditional | Product-native | AssemblyAI accepts uploaded media, supports streaming ingestion, and provides endpoints for retrieving transcripts and (redacted) audio. It does not document native PSTN call recording/originating capabilities; recording must be supplied or coordinated by the integrator and can then be processed (including PII redaction options). |
| Transcription / speech-to-text | Established | Product-native | Full-featured transcription across Pre-recorded, Realtime (streaming), and Sync APIs. Universal-3.5 Pro and other models, speaker diarization, keyterms, summarization, translation, medical mode, and many downstream features. |
| Text-to-speech / voices | Established | Product-native | Voice Agent API returns audio and includes natural-sounding voices; Voice Agent product page documents 'get audio back' and 'select from natural-sounding voices' (also 'Bring your own Voice (TTS)' option). |
| Realtime audio / media streaming | Established | Product-native | Realtime WebSocket streaming API with SDKs (Python/JS), session lifecycle messages, turn transcripts, low-latency partial/final transcripts, and cloud data-residency endpoints. |
| DTMF / speech gather | Not found in reviewed official docs | External integration | Not found in the official documentation reviewed for this profile; this is not a claim that the capability is unsupported. |
| Call logs / analytics / observability | Established | Product-native | Speech Understanding and Conversation Intelligence features (speaker diarization, sentiment, entity detection, summarization) and transcript endpoints enable analytics. Platform also documents uptime SLA and monitoring. |
| Testing / simulation | Limited / conditional | Product-native | Documentation includes SDK quickstarts and a Playground for trying APIs; no dedicated call-simulation/testbed for PSTN flows documented, but sample streams and SDK examples support development/testing. |
| Language support | Established | Product-native | Pre-recorded STT supports 99+ languages; realtime lists flagship realtime coverage (18 languages) and code-switch handling. Translation feature supports translating transcripts into 86 target languages. |
| Security / compliance | Established | Product-native | Enterprise-grade security: encryption (TLS1.3 in transit, AES-256 at rest), access controls, SOC 2 Type 1 & Type 2, PCI-DSS 4.0 Level 1, GDPR assessments, EU data residency, BAA/HIPAA-eligible infrastructure for Medical Mode. |
| Pricing / billing model | Established | Product-native | Pay-as-you-go with no minimums; pre-recorded billed per audio-second (model-rate pro-rated), streaming and Voice Agent billed per WebSocket-open duration (session-based). Per-model rates listed on pricing pages; enterprise invoicing and volume discounts available. |
Capabilities marked “Not found in reviewed official docs” were not located in the official documentation corpus reviewed for this profile; that status does not mean the capability is unsupported.
How AssemblyAI Can Connect to Business Systems
Primary integration patterns in the documentation: (1) upload media + POST a transcript request for pre-recorded audio; (2) Sync API for short clips; (3) realtime WebSocket streaming for low-latency transcripts and Voice Agent sessions; (4) webhooks to receive finalized transcripts. Telephony, PSTN/SIP/trunking and native call-routing/number provisioning were not found in the reviewed official docs and should be provided by an orchestration or telephony layer that forwards/records audio for AssemblyAI to ingest.
Common integration patterns: upload file + POST transcript (pre-recorded), Sync for short clips, WebSocket streaming for realtime/voice agents, and webhooks to receive finalized transcripts — integrate telephony (PSTN/SIP) or RTC layers (LiveKit/Pipecat) to supply/collect audio.
Voice Agent API supports two modes: managed LLM/voice stack (one WebSocket) or bring-your-own stack (use Realtime STT + external LLM/TTS).
Common AssemblyAI Use Cases
Typical flows: stream call audio into AssemblyAI over the Realtime WebSocket to receive partial and final turn transcripts and LLMGateway/Voice-Agent responses; or upload recordings to the Pre-recorded API for batch transcription, diarization, entity extraction and summarization. Use webhooks to receive callbacks for completed transcripts and integrate transcripts/results into analytics or CRM pipelines.
Realtime voice agents via Voice Agent API (stream audio in, get audio/text back)
Low-latency streaming STT for captions or live monitoring
Batch transcription, speaker diarization, entity extraction and summarization
Multilingual translation and code-switch handling for recorded audio
Where AssemblyAI May Be Particularly Strong
Documentation-backed strengths:
Strength 1
Industry-leading STT across pre-recorded, realtime, and sync modes (Universal-3.5 Pro / Universal Streaming)
Strength 2
Production-ready realtime WebSocket streaming with SDKs and low-latency turn transcripts
Strength 3
Comprehensive speech-understanding features (entities, summarization, speaker diarization, sentiment, translation, custom formatting)
Strength 4
Voice Agent API that can return audio and optionally manage LLMs (one WebSocket session)
Strength 5
Enterprise security and compliance (SOC 2, PCI-DSS, GDPR, EU data residency, encryption)
Where AssemblyAI May Not Be the Best Fit
Documented tradeoffs and operational notes:
Consideration 1
No native PSTN/SIP phone-number provisioning or call-routing documented — requires external telephony/RTC orchestration
Consideration 2
Streaming billed per open WebSocket session (must close sessions to avoid charges)
Consideration 3
Realtime language coverage narrower (18 realtime languages) vs pre-recorded (99+ language support)
When Peak Demand May Choose AssemblyAI
When to select AssemblyAI vs building/integrating alternatives:
Best-fit pattern 1
Realtime voice agents, agent assist, live captioning and notetakers
Best-fit pattern 2
Post-call conversation intelligence and analytics pipelines
Best-fit pattern 3
Multilingual transcription and translation workflows
Best-fit pattern 4
Products that can provide audio transport (RTC or uploaded files) and need STT+understanding
When another platform may deserve a closer look
Evaluate alternatives when 1
Systems requiring native PSTN phone number management, SIP trunking, or call routing within the same vendor
Evaluate alternatives when 2
Use-cases that require the vendor to originate/terminate phone calls without external telephony integration
Security, Data Handling & Compliance Considerations
AssemblyAI documents enterprise-grade controls: TLS 1.3 in transit, AES-256 at rest, role-based access controls, vulnerability scanning and auditing. Compliance claims in the official docs include SOC 2 (Type 1 & Type 2), PCI‑DSS 4.0 Level 1, GDPR assessments, EU data residency options, and BAA/HIPAA-eligible infrastructure for Medical Mode.
AssemblyAI documents AES-256 at rest and TLS 1.3 in transit, role-based access controls, pen tests, vulnerability scans, uptime monitoring and auditing practices; SOC 2 Type 1 and Type 2 and PCI-DSS 4.0 Level 1 are cited.
EU Data Residency and BAA/HIPAA-eligible infrastructure available for relevant add-ons (Medical Mode).
How AssemblyAI Pricing Should Be Evaluated
Per the official pricing docs: pay-as-you-go with no minimums. Pre-recorded transcription is billed per audio second (pro-rated to exact seconds). Streaming and Voice Agent usage is billed for the duration a WebSocket session remains open; sessions auto-close after three hours and can incur billing for the open-session duration if not client-terminated. Enterprise invoicing and volume discounts are described on the pricing pages.
Streaming and Voice Agent sessions are billed for total WebSocket-open duration; sessions auto-close after 3 hours and will bill for full 3 hours if not client-terminated — ensure session termination messages are sent to avoid unexpected charges.
Pre-recorded transcription billed pro-rated to exact audio seconds; Sync API returns immediate transcript for short clips and uses model hourly-equivalent pricing.
Testing the Platform Before Production
The documentation includes SDK quickstarts (Python/JS), a Streaming WebSocket API spec, and a Playground for trying APIs. There is no dedicated PSTN call-simulation/testbed documented; sample streams and SDK examples are the recommended paths for development and testing.
What Peak Demand Adds Around AssemblyAI
Implementation checklist from official docs: provision an API key, choose the mode (pre-recorded, sync, realtime, or Voice Agent), and follow SDK quickstarts or the WebSocket API spec. For realtime voice agents, either use the Voice Agent API (single WebSocket that can return audio and drive LLM-managed flows) or combine Realtime STT with an external LLM/TTS. Provide audio via RTC or by uploading media; register webhook URLs to receive callbacks. For production, plan session lifecycle handling (close WebSocket sessions promptly to avoid unnecessary streaming charges) and integrate a telephony/RTC orchestration layer if you need PSTN origination/termination, number provisioning, SIP trunking or call-routing features.
Discovery & Platform Fit
Determine whether the platform is actually the right choice for the workflow before building around it.
Conversation & Agent Architecture
Design prompts, flows, variables, tools, validation, escalation and business logic.
Telephony & Realtime Infrastructure
Configure the appropriate phone, SIP, CPaaS or realtime transport layer for the deployment.
Middleware & APIs
Build controlled AWS, Cloudflare, API, webhook or middleware layers where systems require additional validation and orchestration.
Business-System Integration
Connect CRM, scheduling, EMR/EHR, ERP, databases, helpdesk, ordering, field-service or proprietary software where suitable integration surfaces exist.
QA & Managed Operations
Test workflows, monitor production behavior, review failures, measure outcomes and refine the implementation over time.
AssemblyAI Questions
Does AssemblyAI provide PSTN phone numbers or SIP trunking?
The reviewed official documentation does not include native PSTN phone-number provisioning, SIP trunking or call-routing primitives. The documentation shows common integration patterns that use external telephony or RTC partners to supply audio which AssemblyAI then ingests for STT and speech-understanding.
How is realtime / Voice Agent usage billed?
Documentation states streaming and Voice Agent usage are billed for the duration a WebSocket session is open. Sessions automatically close after three hours; if a session remains open it will be billed for the open-session duration. Pre-recorded transcription is billed per audio second (pro-rated).
Does AssemblyAI support text-to-speech (TTS) and returning audio from a voice agent?
Yes. The Voice Agent API can return audio and the platform documents natural-sounding voices and a 'bring your own voice' (BYO TTS) option in the official product pages.
What speech-understanding features are available?
Official docs list speaker diarization, entity detection, summarization, sentiment, keyterms, translation, custom formatting and medical-mode variants among the Speech Understanding capabilities.
What languages does AssemblyAI support?
Per the documentation, pre-recorded STT supports 99+ languages. Realtime streaming lists flagship coverage for about 18 languages and includes code-switch handling. Translation can render transcripts into 86 target languages.
Are there official SDKs and WebSocket samples?
Yes. Official Python and JavaScript SDKs are provided along with Streaming WebSocket API specs, quickstarts for pre-recorded and realtime flows, and sample code for uploads and streaming sessions.
Can AssemblyAI process recorded PSTN calls?
AssemblyAI accepts uploaded media and realtime streams for processing; however, the reviewed docs do not document native PSTN call recording/origination. Integrators should capture or route PSTN audio through their telephony/RTC layer and supply that audio to AssemblyAI. Uploaded/streamed audio can then be transcribed and processed with available redaction options.
Explore Retell AI
Retell AI is one of the full-stack Voice AI platforms Peak Demand evaluates for phone-first deployments, custom integrations, telephony, APIs, and managed production workflows.
Explore Retell AIPeak Demand may earn a commission from this link.
Planning a AssemblyAI Deployment?
Peak Demand can help evaluate platform fit, design the architecture, connect telephony and business systems, implement controlled tools and integrations, test edge cases, and manage the operational layer after launch.
Discuss a AssemblyAI DeploymentOfficial AssemblyAI Sources Reviewed
This profile is maintained using official or first-party vendor sources. Current vendor documentation remains the source of truth for an active production decision.
Last researched: 2026-08-20
Next recommended review: 2026-11-18
