For live event captions, the “best” speech translation API usually depends on the exact tradeoff you need between latency, language coverage, caption quality, and deployment flexibility. If you want the short version:

Best overall for low-latency live captions

Microsoft Azure Speech Translation

• Strong real-time streaming
• Good multilingual support
• Built for live transcription + translation
• Good enterprise reliability and speaker/caption workflows

Best if you want a very polished end-to-end cloud ecosystem

Google Cloud Speech-to-Text + Translation

• Excellent ASR quality
• Broad language support
• Low-latency streaming options
• Often strong for complex audio, though translation may require chaining services

Best if you care about enterprise customization and deployment control

AWS Transcribe + Amazon Translate

• Reliable streaming transcription
• Good integration with AWS stack
• Flexible for production pipelines
• Translation is usually a separate step, which can add a bit of latency vs. a native speech-translation service

Best if you need broad language support and strong speech recognition

Deepgram

• Very low latency streaming
• Good real-time transcription
• Flexible APIs and strong developer experience
• For translation, you’d typically pair it with a translation model/service

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My recommendation

If your main goal is live event captions with minimal delay and built-in translation, I’d start with:

1. Azure Speech Translation for the most direct “speech → translated captions” workflow
2. Google Cloud if you prioritize transcription accuracy and can manage a two-step pipeline
3. Deepgram + translation API if latency is critical and you want more control

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What matters most in this use case

When choosing, look at:

• End-to-end latency: under 1–2 seconds is ideal for live captions
• Streaming support: true partial/interim results matter a lot
• Language pairs: some services support many source languages, but not all target languages equally well
• Punctuation and diarization: important for readable captions
• Stability under noisy audio: conferences, microphones, panel discussions
• Compliance / data residency: often important for events
• Caption formatting: ability to produce WebVTT/SRT or live caption overlays

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Practical pick by scenario

• Conference / webinars / multilingual streaming: Azure Speech Translation
• High-accuracy transcription with flexible downstream processing: Google Cloud
• Developer-first, low-latency streaming pipeline: Deepgram + translation
• AWS-native infrastructure: AWS Transcribe + Amazon Translate

If you want, I can also give you a side-by-side comparison table of Azure vs Google vs AWS vs Deepgram specifically for latency, language coverage, and live caption use.