Compare realtime APIs
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| Cartesia Ink (ink-2, ink-whisper) Cartesia | Soniox Real-time STT (stt-rt-v5) Soniox | AssemblyAI Universal-3.6 Pro Realtime and Universal-Streaming AssemblyAI | |
|---|---|---|---|
| Category | Speech-to-text | Speech-to-text | Speech-to-text |
| Status | GA | GA | GA |
| Est. per minute | $0.0022 - 0.012 | $0.002 - 0.0025 | $0.0025 - 0.0095 |
| How that was worked out | ink-whisper on Scale ($0.13/hr) up to ink-2 on Pro overage (10,800 credits/hr x $65/1M = $0.70/hr). | ~$0.12/hr vendor estimate = $0.002/min; higher with long context prompts or translation output. | $0.15/hr Universal-Streaming = $0.0025/min; $0.45/hr U3.6 Pro + $0.12/hr diarization = $0.0095/min. Session time, so idle open sockets cost the same. |
| Pricing model | per-hour | per-token | per-hour |
| Free tier | Free plan: 20K credits/month (about 1h51m of ink-2 per plan table). | Not stated on the pricing page. | $50 free credit at signup, no card required. |
| Connects by | WebSocket | WebSocket | WebSocket |
| Audio in | encoding pcm_s16le, pcm_s32le, pcm_f16le, pcm_f32le, pcm_mulaw, pcm_alaw with explicit sample_rate; ~100 ms binary chunks. | audio_format 'auto' for containers, or raw PCM: pcm_s8/s16/s24/s32, unsigned u8-u32, float f32/f64 (le/be), with sample_rate and num_channels. | Mono 16-bit PCM by default with sample_rate set to the source; mulaw also documented historically; AAC (ADTS, encoding=aac) and Opus (encoding=ogg_opus or opus) accepted. Chunks must be 50-1000 ms and must not arrive faster than real time. |
| Audio out | n/a | n/a | n/a |
| Languages | ink-whisper takes an ISO-639-1 language (default en); ink-2 language coverage not captured. | 60+ languages with language identification and mixed-language robustness; realtime translation across 3,600+ language pairs (vendor). | Universal-3.6 Pro: 32 languages with code-switching; 3.5 Pro: 19; Universal-Streaming Multilingual: 6; English model: English only. |
| Latency (vendor claim) | No numeric claim captured. | No numeric vendor claim captured; model notes cite 'faster semantic endpointing'. | Vendor docs rate the Pro models 'Fastest' and Universal-Streaming 'Fast'; no numeric figure on the model page. |
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| Compliance | Enterprise plans list DPAs and BAAs; not re-verified. | Not re-verified in this pass. | US and EU data-zone streaming endpoints documented. Vendor markets SOC 2 and HIPAA BAA; not re-verified in this pass. |
| Self-hostable | No | No | Yes |
| Last checked | 2026-10-10 | 2026-10-10 | 2026-10-10 |
| Key numbers and features | |||
| $/hour | $0.39 | $0.12 | $0.45 |
| Bills silence | Yes | - | Yes |
| Free tier | Yes | - | Yes |
| Free credit $ | - | - | $50 |
| Live speakers | - | Yes | Yes |
| Turn detect | Yes | Yes | Yes |
| Keyterms | Yes | Yes | Yes |
| PII redact | - | - | Yes |
| Partials | Yes | Yes | Yes |
| Mixed langs | - | Yes | Yes |
| 8 kHz phone | Yes | - | - |
| Latency ms | - | - | - |
| Languages | - | 60 | 32 |
| Max session min | - | 300 | 180 |
| Concurrency | 12 | 10 | - |
| WebRTC | No | No | No |
| WebSocket | Yes | Yes | Yes |
| gRPC | No | No | No |
| HIPAA | Yes | - | Yes |
| SOC 2 | - | - | Yes |
| EU data | - | - | Yes |
| Self-host | No | No | Yes |
| Open weights | No | No | No |
| High warnings | 1 | 1 | 2 |