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Documentation Index

Fetch the complete documentation index at: https://docs.gradium.ai/llms.txt

Use this file to discover all available pages before exploring further.

This page summarises the request-level limits that apply to Gradium API calls. For pricing and credit consumption see Credits.

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Session duration

A single TTS or STT session can last up to 300 seconds. This applies to both the WebSocket and REST POST transports. If you need to generate or transcribe longer content, split it across multiple sessions:
  • TTS: chunk text at sentence boundaries and start a new session for each chunk (or open a new WebSocket and send a fresh setup).
  • STT: split audio at silences and submit each segment as a separate request.

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Supported audio formats

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TTS output formats

output_format accepts:
  • wav: WAV at 48 kHz, 16-bit signed mono.
  • pcm: raw PCM at 48 kHz, 16-bit signed mono, 3840-sample (80 ms) chunks.
  • opus: Ogg-wrapped Opus.
  • Lower / higher sample-rate PCM variants: pcm_8000, pcm_16000, pcm_22050, pcm_24000, pcm_44100, pcm_48000.
  • Telephony: ulaw_8000 (alias mulaw_8000) and alaw_8000.

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STT input formats

For STT WebSocket (input_format setup field) and STT REST (Content-Type header or input_format query parameter), supported formats are:
  • WAV with PCM data, 16/24/32-bit (audio/wav, input_format: "wav").
  • Raw PCM, 16-bit signed little-endian, mono. The bare value "pcm" defaults to 24 kHz; explicit rates "pcm_8000", "pcm_16000", "pcm_22050", "pcm_24000", "pcm_44100", "pcm_48000" are also accepted (audio/pcm for the REST Content-Type).
  • Ogg-wrapped Opus (audio/ogg or audio/opus, input_format: "opus").
  • Telephony: mu-law ("ulaw_8000" / "mulaw_8000") and A-law ("alaw_8000") encoded PCM at 8 kHz.
Convert your input to one of the formats above before uploading.

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Concurrency

Concurrent session limits depend on your plan. Contact support@gradium.ai for the exact limits on your tier.