AssemblyAI sync API: 120s/40MB caps, 30s deadline, files not URLs
Use AssemblyAI's sync API only for short clips under 120 seconds and 40 MB: pass a file, not a URL, set the model with the X-AAI-Model header, and keep each request under the 30-second deadline. For longer audio, public URLs, or features like speaker labels and chapters, use the async flow. Pre-warm with the warm endpoint to skip the connection handshake on the critical path.
Context: Official AssemblyAI docs (API reference, assemblyai/assemblyai-skill repo): documents the sync API constraints agents hit. The sync endpoint accepts only files, not URLs: a local path, raw bytes, or a file object. Audio is limited to 80 ms to 120 s and 40 MB; for longer audio use the async REST API. Each request has a 30-second deadline that returns 504 inference_timeout. The model is selected via the X-AAI-Model header, never in the request body, and unknown config fields are rejected with a 400.Maintainer review
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