Google Speech-to-Text vs. AssemblyAI

Learn why developers choose AssemblyAI to build powerful Voice AI apps that exceed industry standards:

Far more reliable speaker diarization (35.21% vs 57.14% cpWER)
Faster streaming—335ms median turnaround vs 878ms
Lower pay-as-you-go pricing with no spend minimums

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Universal-3.5 Pro

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At a glance: Google Speech-to-Text vs. AssemblyAI

Model

AssemblyAI Universal-3.5 Pro

Google Speech-to-Text

Speaker diarization (cpWER)

35.21%

57.14%

Streaming semantic word error rate

1.34%

2.85%

Streaming latency (median time-to-complete-turn)

335 ms

878 ms

Pre-recorded pricing (pay-as-you-go)

$0.21 / hour

$0.96 / hour

Real-time pricing (pay-as-you-go)

From $0.15 / hour

$0.96 / hour

Free tier

$50 in free credits

60 min / month

Unlimited concurrency

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Apply any LLM to transcripts (LLM Gateway)

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BAA available

Go beyond transcription with Assembly's full Voice AI Infrastructure

Best-in-Class Accuracy

Universal-3.5 Pro is the most accurate, controllable model on the market, with industry-leading accuracy on real-world audio—noisy environments, accents, and technical vocabulary—plus best-in-class recognition of names, emails, and numbers.

Realtime Streaming

Ultra-low-latency streaming transcription (~300ms) purpose-built for voice agents, with immutable transcripts and native code-switching.

Speaker Diarization

Built-in speaker labels on pre-recorded and streaming audio, with each word in the transcript associated to its speaker.

Lower, Usage-Based Pricing

Pay only for what you use—$0.21/hr batch and real-time from $0.15/hr—with $50 in free credits and no minimum commitments or contracts.

LLM Gateway

Route 25+ leading LLMs through one OpenAI-compatible API to build Q&A, summaries, extraction, and agentic workflows on your transcripts.

Speech Understanding

Layer summarization, sentiment analysis, topic detection, and auto chapters on top of every transcript.

PII Redaction & BAA

Detect and redact PII from transcripts and audio, and sign a BAA for apps that process PHI.

Proven Reliability and Security

Deploy on infrastructure that processes millions of hours daily, with 99.9% uptime, unlimited concurrency, and SOC 2 Type 2, ISO 27001, PCI DSS, and GDPR.

Start building

Get your free API key and ship your first transcript in minutes—no commitments or minimums.

Ready to move beyond Google Speech-to-Text?

Switch to more reliable diarization, faster streaming, and lower pay-as-you-go pricing—with no contracts or spend minimums.

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Investments in STT improvements always pay for themselves, since it is such a critical building block of the voice pipeline.

Lindsay Liu, Co-Founder & CEO at Super

Playground

We're not playing around—but you can

Test our best-in-class speech-to-text and voice agent models in our no-code playground.

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Frequently asked questions

: AssemblyAI leads in AssemblyAI’s benchmarks (assemblyai.com/benchmarks): Universal-3.5 Pro records a 35.21% diarization error rate (cpWER) versus 57.14% for Google, and in the Pipecat STT Benchmark it records a 1.34% streaming semantic word error rate versus 2.85% for Google STT. Always test both on your own audio.
: Yes, for standard usage. AssemblyAI’s pre-recorded transcription is $0.21 per hour and real-time starts at $0.15 per hour, versus $0.96 per hour ($0.016/min) for Google Speech-to-Text V2 standard recognition. Google offers a lower-priced dynamic batch mode ($0.18 per hour), but it runs in a lower-priority queue with slower turnaround, while AssemblyAI’s $0.21 rate applies to standard fast-turnaround transcription.
: AssemblyAI. In the Pipecat STT Benchmark cited on assemblyai.com/benchmarks, Universal-3.5 Pro Realtime returns final transcripts in a median of 335ms after the speaker stops talking, versus 878ms for Google STT—a meaningful difference for voice agents and live captioning.
: Google supports a broader language catalog (125+ languages), while AssemblyAI supports 99 languages with automatic language detection. For speaker diarization, AssemblyAI is significantly more reliable in AssemblyAI’s benchmarks (35.21% vs 57.14% cpWER), so if multi-speaker audio matters, evaluate both on your own data.
: No. AssemblyAI is a managed API that works alongside your existing GCP infrastructure—you can keep audio in Cloud Storage and submit publicly accessible or signed URLs for transcription, then store results wherever your stack lives.
: Yes. AssemblyAI publishes a step-by-step Google Speech-to-Text-to-AssemblyAI migration guide with side-by-side code, and SDKs are available in Python, TypeScript, Go, Java, and Ruby. Most teams switch with minimal code changes—no encoding or sample-rate configuration required.