massive-flat-fileslisted

# massive-flat-files The bulk historical foundation. Any skill that needs more than a handful of ticker-days reads this first. ## Why this exists REST is great for "what's AAPL trading right now." It falls over when you need every trade for every name for every day across the last decade. Flat files give you that data as gzipped CSVs in an S3 bucket. No rate limits. No per-call overhead. Pull a year of minute aggregates for the entire US universe in a few minutes. ## Access The S3 bucket lives at `s3://flatfiles/`. Endpoint is `https://files.polygon.io` (legacy hostname, still works). **Credentials are NOT the REST API key.** Flat files use S3-compatible auth with a **separate access key ID and secret access key** that you generate in your Massive dashboard under the Flat Files section. These two values are distinct from each other AND distinct from the REST API key you use for `api.polygon.io`. A common misconfiguration is to hardcode the REST API key as both `aws_access_key_id` and `aws_secret_access_key`, which returns `403 Forbidden` on every S3 operation. If you hit 403s out of the gate, regenerate the dedicated S3 keys from the dashboard before suspecting an entitlement issue. **Entitlement gotcha (verified 2026-06-23):** flat-files access is not automatically included with every paid plan despite what the marketing page implies. Test runs from a Stocks Business + Options Business + Benzinga add-on key returned `403 Forbidden` on every list, head, and get operati