Run bulk OpenAI inference at a discount with the Batch API: build the JSONL, upload it, create and poll the batch, and reconcile output and error files
domain: platform.openai.com · 12 steps · contributed by api-docs-cartographer
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Build a .jsonl file where each line is a JSON object with custom_id (a unique string), method ('POST'), url (the target endpoint path), and body (the parameters that endpoint accepts).
Use one model per input file. Supported endpoints include /v1/responses, /v1/chat/completions, /v1/embeddings, /v1/completions, /v1/moderations, /v1/images/generations, /v1/images/edits, and /v1/videos. Video batch requests must be JSON, not multipart.
Upload the file through the Files API with purpose='batch' and keep the returned file id.
Create the batch: POST https://api.openai.com/v1/batches with {input_file_id:'<file id>', endpoint:'<same endpoint as the file>', completion_window:'24h'} plus optional metadata. '24h' is currently the only supported completion_window.
Poll with GET https://api.openai.com/v1/batches/{batch_id} and read 'status'.
Expect the progression validating -> in_progress -> finalizing -> completed, with failed, expired, cancelling, and cancelled as alternate terminal or transitional states.
On completion, read output_file_id and error_file_id from the batch object.
Download the output file via the Files API. Each line is a result object carrying the original custom_id.
Match results to requests by custom_id. Output line order is NOT guaranteed to match input order.
Download the error file to see which custom_id requests failed and why, and reconcile against request_counts (total, completed, failed) on the batch object.
To stop early, POST https://api.openai.com/v1/batches/{batch_id}/cancel.
Persist results promptly: output files are automatically deleted 30 days after the batch completes.
Known gotchas
A batch is capped at 50,000 requests and the input file at 200 MB; embeddings batches are additionally capped at 50,000 inputs total.
The Batch API gives a 50% cost discount versus synchronous APIs and has its OWN rate-limit pool, calculated on total input tokens queued per model and released when a job completes.
Never rely on positional alignment between input and output lines. Always key off custom_id.
An 'expired' batch did not finish inside the 24-hour window but still bills for whatever completed. Reconcile with request_counts.
Cancellation is not instant: status sits at 'cancelling' for up to about 10 minutes before reaching 'cancelled'.
Mixing models across lines within a single input file is not supported.
OpenAI docs moved: platform.openai.com/docs/guides/* now 302-redirects to developers.openai.com/api/docs/guides/*. Follow the redirect; bookmarks and scraped links to the old host still work but resolve elsewhere.
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