Sync API or Dictation API? How to pick for your dictation feature

AssemblyAI’s Sync and Dictation APIs use the same Universal-3.5 Pro speech-to-text model, accept up to 120 seconds of WAV or raw 16-bit PCM audio, and support pre-warming and audio upload during recording, but differ in their outputs and intended applications. Sync returns only a verbatim transcript, making it better suited to regulated records, spoken-punctuation workflows, word-level timestamping, voice-agent turns with conversational context, custom downstream cleanup, and cost-sensitive deployments at $0.45 per audio hour. Dictation costs $0.62 per hour and adds an LLM-generated cleaned version alongside the unchanged transcript, removing filler, resolving self-corrections, and adding formatting for text intended to be sent directly, while allowing customizable output instructions and falling back to the raw transcript if cleanup times out. The cleanup layer improves readability rather than transcription accuracy, so specialized names, terms, and jargon should be supplied through key-term prompting, while contextual prompts can describe the expected audio domain. Dictation necessarily adds some latency because it performs a second processing pass, although both APIs typically process short clips in under a second and expose timing metrics. For recordings longer than two minutes, such as extended clinical notes, the recommended approach is chunking or streaming transcription followed by cleanup of the assembled text.

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