Multimodal inputs

	Chat Completions	Responses	Messages
Image	`{"type": "image_url", "image_url": {"url"}}` with an `https` URL or a data URI	`{"type": "input_image", "image_url"}`	`{"type": "image", "source"}` with `base64` or `url`
File or PDF	`{"type": "file", "file": {"filename", "file_data"}}` with a data URI, or `{"file_url"}`	`{"type": "input_file", "filename", "file_data"}` or `file_url`	`{"type": "document", "source"}` with `base64`, `url` or `text`
Audio	`{"type": "input_audio", "input_audio": {"data", "format"}}`	`{"type": "input_audio", ...}`	Not accepted

Rules

Check what the model accepts. architecture.input_modalities in /v1/models lists text, image, audio and file. Sending another type fails with 400 unsupported_modality before the request reaches a provider.
Size. One inline image, file or audio part can be up to 20 MiB, and the whole request up to 32 MiB.
Files by value or by link. Send files as base64 or as an https link. NagaAI has no Files API, so a file_id fails with 400 file_id_unsupported. Models without native file input receive the text of the file.
Audio formats. input_audio.data is raw base64. A data: prefix fails with 400. format is one of wav, mp3, aiff, aac, ogg, flac, m4a, pcm16, pcm24.
Messages documents. NagaAI drops a document with a content source. Use base64, url or text.