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AssemblyAI vs Cartesia
AssemblyAI is positioned as transcription APIs for live and recorded audio, with model-specific language and analysis options. Cartesia is positioned as speech models for teams assembling a voice stack, with a separate managed-age
AssemblyAI is positioned as transcription APIs for live and recorded audio, with model-specific language and analysis options. Cartesia is positioned as speech models for teams assembling a voice stack, with a separate managed-agent product. Start by deciding who owns the missing layers, then inspect the documented differences below.
STT and Voice Engines are different product categories. An underlying engine or framework is not a complete substitute for a deployed agent workflow.
9 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 | Cartesia |
|---|---|---|
| Billing unitDifferent records | Async audio hours; streaming connection hours; agent session minutes; gateway tokens | TTS/STT credits; Managed Agents conversation minutes |
| Bring your telephonyDifferent records | Yes | Yes |
| Bring your modelDifferent records | Yes | Yes |
| HIPAA pathDifferent records | Yes | Yes |
| WebhooksDifferent records | YesUnknown | YesAPI / webhook |
| Billing modelShared state | component-stack | component-stack |
Your requirements & next steps
Your requirements
Ready-made / AI receptionist · Strict evidence mode
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STT hours/session duration, agent minutes, gateway tokens and add-ons remain distinct.
TTS/STT credit subscriptions and Managed Agents minute charges remain separate.
Model rates are scoped; add-ons stack; reference states updated May 29, 2026 and conflicts are retained.
Speech model credits and selected LLM/evaluation charges have separate scope.
Idle streaming connection duration is billable. No fabricated all-in phone cost per minute.
Product-specific units preserved.
SSO costs $199 per connection per month; do not mistake no base fee for no fixed optional charges.
Plan allowances include separate agent prepayment; do not double-count as universal included voice minutes.
Not a fixed monthly audio allowance; credits do not expire.
Separate credit and agent budgets; no arbitrary cross-product minute conversion.
No invented bundle overage.
Free allowances and product rates are available; old changelog, bandwidth trial and speech volume controls do not establish these current billing terms.
Component choices and call mix must be specified.
LLM promotion ends October 1, 2026; quoted model/usage mix determines bill.
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.
Product mix, LLM promotion expiry, carrier routing and other metered components prevent a universal all-in ceiling.
No complete phone bill ceiling from minutes alone; carrier, model and addon scope vary.
Product mix, LLM promotion expiry, carrier routing and other metered components prevent a universal all-in ceiling.
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.
Cartesia
A speech credit plan is not a complete phone-call bill.
Managed Agents $0.06/min; Cartesia-provided-number telephony $0.014/min · V3.3 evidence review · Managed Agents base rate; carrier/model charges and prepaid plan balances separate
Excluded / confirm: Complete cost cannot be established from this reference. Product mix, LLM promotion expiry, carrier routing and other metered components prevent a universal all-in ceiling. · LLM tokens after promotional coverage; telephony and evaluation usage
TTS/STT credit subscriptions and Managed Agents minute charges remain separate.
The evidence overlap.
Both records have documented values for Product type, Technical setup, Pricing model, Published numeric pricing, Realtime / streaming audio, Function / tool calling, Published included concurrency at least, 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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