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Cartesia vs OpenAI Realtime API
Cartesia is positioned as speech models for teams assembling a voice stack, with a separate managed-agent product. OpenAI Realtime API is positioned as speech-to-speech API for developers implementing their own voice application.
Cartesia is positioned as speech models for teams assembling a voice stack, with a separate managed-agent product. 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.
Voice Engines and Developer Frameworks 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 | Cartesia | OpenAI Realtime API |
|---|---|---|
| Billing unitDifferent records | TTS/STT credits; Managed Agents conversation minutes | 1 million text/audio/image tokens; transcription separately metered |
| Bring your modelDifferent records | Yes | Unknown |
| HIPAA pathDifferent records | Yes | Unknown |
| WebhooksDifferent records | YesAPI / webhook | YesUnknown |
| Billing modelShared state | component-stack | component-stack |
| Bring your telephonyShared state | Yes | Yes |
Your requirements & next steps
Your requirements
Ready-made / AI receptionist · Strict evidence mode
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TTS/STT credit subscriptions and Managed Agents minute charges remain separate.
Realtime model tokens plus input transcription, tools and carrier/hosting; not GPT-Live session-minute billing.
Speech model credits and selected LLM/evaluation charges have separate scope.
Cached audio/text and image inputs have separate rates. Rate is not per-minute.
Product-specific units preserved.
Model scope fixed to GPT-Realtime-2, not all voice models.
Plan allowances include separate agent prepayment; do not double-count as universal included voice minutes.
Published Realtime token rates do not establish these account/contract terms. GPT-Live duration billing and unrelated fine-tuning discounts must not be imported.
Separate credit and agent budgets; no arbitrary cross-product minute conversion.
Published Realtime token rates do not establish these account/contract terms. GPT-Live duration billing and unrelated fine-tuning discounts must not be imported.
Free allowances and product rates are available; old changelog, bandwidth trial and speech volume controls do not establish these current billing terms.
Published Realtime token rates do not establish these account/contract terms. GPT-Live duration billing and unrelated fine-tuning discounts must not be imported.
LLM promotion ends October 1, 2026; quoted model/usage mix determines bill.
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.
Product mix, LLM promotion expiry, carrier routing and other metered components prevent a universal all-in ceiling.
Full bill requires measured model/token/cache/tool/carrier usage; conversation minutes alone are insufficient.
Product mix, LLM promotion expiry, carrier routing and other metered components prevent a universal all-in ceiling.
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.
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.
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, Function / tool calling, Official product documentation, 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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