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Python speech-to-text API

The speech-to-text API for Python developers

Transcribe pre-recorded audio or live streams in a few lines of Python. One API returns accurate text with timestamps, speaker labels, and language detection—at any scale. Start free, no credit card.

Audio files to text

Send a local file or URL—MP3, WAV, MP4, and more—and get back formatted text with word-level timestamps and speaker labels.

Real-time streaming

Stream mic or telephony audio over a WebSocket and transcripts come back within a few hundred milliseconds.

A real Python SDK

pip install assemblyai covers both—the SDK handles upload, submission, and polling, so there's no queue plumbing to write.

Metaview
Ashby
Cluely
Genio
Siro

36%

improvement in close rate

See case study
LiveKit
Earmark
Commure
Dovetail
Fireflies

“The new Universal-3.5 Pro speech model from AssemblyAI is best so far in terms of accuracy, latency, and language switching.”

Retell
CallRail
Apollo.io
ClickUp
Calabrio

80%

increase in customer satisfaction

HeyGen
Granola
Siro
JotPsych
Granola

“Assembly has saved us countless hours managing models, and provided exceptional accuracy.”

Metaview
Ashby
Cluely
Genio
Siro

36%

improvement in close rate

See case study
LiveKit
Earmark
Commure
Dovetail
Fireflies

“The new Universal-3.5 Pro speech model from AssemblyAI is best so far in terms of accuracy, latency, and language switching.”

Retell
CallRail
Apollo.io
ClickUp
Calabrio

80%

increase in customer satisfaction

HeyGen
Granola
Siro
JotPsych
Granola

“Assembly has saved us countless hours managing models, and provided exceptional accuracy.”

Library vs API

When a Python library isn't enough

Open-source libraries like SpeechRecognition, Vosk, and Whisper are a fine way to prototype—if you're up for managing models, GPUs, and accuracy tradeoffs yourself. An API moves that work onto managed infrastructure: you send audio, and accurate transcripts come back with speakers, timestamps, and 99+ languages—whether you're processing one file or a million.

Start building free

No credit card required

Word error rate

Word error rate is the share of words the model gets wrong against a human reference—the standard measure of transcription accuracy on pre-recorded audio.

Pre-recorded word error rate on English audio.

*Lower is better*
Pre-recorded word error rate (English)
AssemblyAI Universal-3.5 Pro
4.35%
OpenAI GPT-4o Transcribe
5.34%
Deepgram Nova-3
6.66%
Azure Batch
7.02%

Source: AssemblyAI published benchmarks — assemblyai.com/benchmarks.

Common questions