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AssemblyAI vs OpenAI Realtime API
AssemblyAI is positioned as transcription APIs for live and recorded audio, with model-specific language and analysis options. OpenAI Realtime API is positioned as speech-to-speech API for developers implementing their own voice a
AssemblyAI is positioned as transcription APIs for live and recorded audio, with model-specific language and analysis options. OpenAI Realtime API is positioned as speech-to-speech API for developers implementing their own voice application. Start by deciding who owns the missing layers, then inspect the documented differences below.
STT and Developer Frameworks are different product categories. An underlying engine or framework is not a complete substitute for a deployed agent workflow.
10 jointly documented catalog fields. This measures evidence coverage, not equivalent quality or an overall winner.
Test opening hours, booking conflicts and an unanswered transfer.
Start where the records differ.
Values and evidence states are compared together. Shared facts follow the differences; Unknown never means No.
| Decision point | AssemblyAI | OpenAI Realtime API |
|---|---|---|
| Billing unitDifferent records | Async audio hours; streaming connection hours; agent session minutes; gateway tokens | 1 million text/audio/image tokens; transcription separately metered |
| Bring your telephonyDifferent records | Yes | Yes |
| Bring your modelDifferent records | Yes | Unknown |
| HIPAA pathDifferent records | Yes | Unknown |
| Billing modelShared state | component-stack | component-stack |
| Warm transferShared state | Unknown | Unknown |
Your requirements & next steps
Your requirements
Ready-made / AI receptionist · Strict evidence mode
No personal requirements yet. Add criteria in Advanced Filter to prioritize this comparison.
STT hours/session duration, agent minutes, gateway tokens and add-ons remain distinct.
Realtime model tokens plus input transcription, tools and carrier/hosting; not GPT-Live session-minute billing.
Model rates are scoped; add-ons stack; reference states updated May 29, 2026 and conflicts are retained.
Cached audio/text and image inputs have separate rates. Rate is not per-minute.
Idle streaming connection duration is billable. No fabricated all-in phone cost per minute.
Model scope fixed to GPT-Realtime-2, not all voice models.
SSO costs $199 per connection per month; do not mistake no base fee for no fixed optional charges.
Published Realtime token rates do not establish these account/contract terms. GPT-Live duration billing and unrelated fine-tuning discounts must not be imported.
Not a fixed monthly audio allowance; credits do not expire.
Published Realtime token rates do not establish these account/contract terms. GPT-Live duration billing and unrelated fine-tuning discounts must not be imported.
No invented bundle overage.
Published Realtime token rates do not establish these account/contract terms. GPT-Live duration billing and unrelated fine-tuning discounts must not be imported.
Component choices and call mix must be specified.
Repeated context, cache behavior and turn count affect token charges.
Not yet researched against this buyer-critical field standard.
Not yet researched against this buyer-critical field standard.
No complete phone bill ceiling from minutes alone; carrier, model and addon scope vary.
Full bill requires measured model/token/cache/tool/carrier usage; conversation minutes alone are insufficient.
No complete phone bill ceiling from minutes alone; carrier, model and addon scope vary.
Full bill requires measured model/token/cache/tool/carrier usage; conversation minutes alone are insufficient.
Anyone with this link can view the encoded decision criteria.
Vendor documentation establishes a claim. Public model benchmarks are separate context, not measurements of these platforms.
Open saved comparison ↗What to verify together.
AssemblyAI
A transcription hour is not a complete agent hour.
Universal-2 async / Universal-Streaming $0.15/hour; U3.5 Pro async $0.21/hour; U3 realtime $0.45/hour; Voice Agent $0.075/min · V3.3 evidence review · Voice Agent API reference; standalone STT is hourly; transport/add-ons separate
Excluded / confirm: Complete cost cannot be established from this reference. No complete phone bill ceiling from minutes alone; carrier, model and addon scope vary. · Twilio carrier; optional custom/Gateway LLM; standalone STT add-ons and per-channel billing
STT hours/session duration, agent minutes, gateway tokens and add-ons remain distinct.
OpenAI Realtime API
A token rate cannot be compared directly with a bundled call-minute price.
GPT-Realtime-2 audio input $32/M, audio output $64/M; text input $4/M, output $24/M · V3.3 evidence review · GPT-Realtime-2 input audio tokens only; output/audio/text/cache have different rates; not 2.1 rate evidence
Excluded / confirm: Complete cost cannot be established from this reference. Full bill requires measured model/token/cache/tool/carrier usage; conversation minutes alone are insufficient. · Input transcription, tool/backend calls, carrier and application infrastructure
Realtime model tokens plus input transcription, tools and carrier/hosting; not GPT-Live session-minute billing.
The evidence overlap.
Both records have documented values for Product type, Technical setup, Pricing model, Published numeric pricing, Realtime / streaming audio, OpenAI models, Function / tool calling, Interruption controls, Checked within 30 days, Retained price snapshot. Matching availability does not measure behavior under your call conditions.
Run the same booking, tool failure and unsuccessful human-transfer cases. Record both outcomes and billable units before signing a deployment agreement.
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