Soniox vs AssemblyAI
for Japanese speech-to-text
Higher accuracy, real-time fluency, and two-way translation for Japanese at lower cost.
Developers choose Soniox for real-time fluency in Japanese
Japanese is spoken by 125 million people worldwide — primarily in Japan, with speakers around the world. For developers, delivering accurate, real-time transcription and translation in Japanese is critical. Soniox provides production-ready transcription and two-way translation for Japanese, handling regional accents, code-switching, and messy real-world audio.
AssemblyAI is known for simple-to-use APIs, but when it comes to Japanese transcription, Soniox outperforms with higher accuracy in real-world audio, true real-time streaming with token-level output in milliseconds, and global coverage with built-in translation across 60+ languages (including Japanese) in one API.
Cleaner transcripts
Soniox delivers 8.7% WER in Japanese vs 14.8% for AssemblyAI, meaning more accurate Japanese transcripts with less cleanup.
One API for 60+ languages
Transcribe and translate Japanese and 60+ other languages in real time or async, without stitching multiple APIs.
Streaming that feels instant
Token-level results in milliseconds make Japanese conversations fast, fluid, and human.
Helping startups and enterprises ship real world voice apps
See the difference for yourself
Don’t just take our word for it. Run the same Japanese audio through Soniox and AssemblyAI in real time and compare live results, side by side.
This demo isn’t pre-recorded. It makes real API calls to AssemblyAI and Soniox in real time, with each service tuned for its best performance. The framework is open source, so you can inspect or run it yourself.
Soniox vs AssemblyAI at a glance
| Feature | Sonioxstt-rt-preview-v2 | AssemblyAIUniversal |
|---|---|---|
| Single Multilingual Model | ||
| Language Hints | ||
| Language Identification | ||
| Speaker Diarization | ||
| Customization | ||
| Timestamps | ||
| Confidence Scores | ||
| Translation One Way | ||
| Translation Two Way | ||
| Endpoint Detection | ||
| Manual Finalization |
And the benchmarks back it up.
In a 2025 study across 60 languages and real-world YouTube audio, Soniox reached 8.7% WER in Japanese vs 14.8% for AssemblyAI.
View the full benchmark report »
Built for accuracy, speed, and scale
Accuracy you can trust in production.
Soniox consistently delivers top results for Japanese, with a 8.7% WER in Japanese vs 14.8% for AssemblyAI. That means cleaner transcripts, less post-editing, and apps you can actually trust in production.
AssemblyAI lags behind in accuracy, especially as audio gets more complex.
Global ready in one API.
Soniox includes transcription and two-way translation for Japanese and 60+ languages, plus speaker detection, timestamps, and diarization – all in one API.
AssemblyAI only handles transcription, forcing developers to chain extra services for translation or multilingual coverage.
Speech-to-text with zero delay.
Soniox streams token-by-token in milliseconds, so Japanese conversations feel live and human.
AssemblyAI processes in chunks, creating noticeable delays that break the flow of live apps.
Designed for messy, real-world conversations.
Soniox handles real-world speech: speaker changes, interruptions, code-switching, and multilingual shifts in Japanese.
AssemblyAI doesn’t support real-time translation, diarization, or multilingual detection, leaving you to patch it together.
Pay up to 3x less than AssemblyAI
With Soniox, transcription, streaming, translation, diarization, timestamps, and confidence are all included in one price. AssemblyAI charges more for their flagship Universal models, while their lower-cost Nano models come with tradeoffs in accuracy.
Effective hourly cost (typical speech)
Soniox: ~$0.10/hour (async), ~$0.12/hour (streaming)
AssemblyAI: ~$0.27 (universal async), ~$0.15/hr (streaming), ~$0.12/hr (nano async)
| Soniox (async) | Soniox (streaming) | AssemblyAI (nano) | AssemblyAI (universal) | AssemblyAI (streaming) | |
|---|---|---|---|---|---|
| 100 hours | ~$10 | ~$12 | ~$12 | ~$27 | ~$15 |
| 1,000 hours | ~$100 | ~$120 | ~$120 | ~$170 | ~$150 |
| 1,000 hours | ~$1,000 | ~$1,200 | ~$1,200 | ~$1,700 | ~$1,500 |
Takeaway: Soniox costs up to 3x less than AssemblyAI, while including translation and richer real-time features out of the box. AssemblyAI’s cheaper models cut accuracy, while Soniox includes full accuracy and features at one flat rate.
Notes:
- Soniox bills per token, which works out to the effective hourly rates above for typical conversational speech.
- AssemblyAI pricing varies by model. Nano is cheaper but sacrifices accuracy; Universal is higher accuracy but more expensive.
- All comparisons use publicly listed rates as of 2025.
Frequently asked questions about Soniox vs AssemblyAI
How accurate is AssemblyAI in Japanese compared to Soniox?
In 2025 benchmarks, AssemblyAI had an 14.8% WER on Japanese speech, versus 8.7% for Soniox. Expect even greater gains in Japanese, especially with messy, real-world audio.
Does AssemblyAI support Japanese translation?
No. AssemblyAI only provides transcription. If you need translation, you’ll have to integrate a separate service. Soniox includes two-way real-time translation across 60+ languages in the same API.
How fast is AssemblyAI’s streaming?
AssemblyAI streams in chunks, which can add noticeable lag in Japanese conversations. Soniox streams token-by-token in milliseconds, so conversations feel natural and responsive.
What about multilingual or messy audio?
AssemblyAI is built for transcription only. It doesn’t support automatic language identification, speaker diarization, or endpoint detection in real time. Soniox includes all of these by default, so it works better in real-world, multilingual conversations.
How does AssemblyAI pricing compare to Soniox?
AssemblyAI’s lower-end models are roughly similar in price, but Universal costs nearly 3× more. Soniox stays flat at ~$0.10–0.12/hr with all features included.
Why is Soniox more cost-efficient?
With Soniox, all features are included by default – transcription, translation, diarization, timestamps, and confidence. AssemblyAI charges more for Universal models while still only offering transcription, meaning you’d need additional services to match Soniox’s end-to-end coverage.
Soniox surpasses AssemblyAI in any language
Get the most accurate, real-time speech-to-text transcription and translation in 60+ languages
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