Massive Flat Files 2026: Polygon.io S3 Data by Plan

Massive (formerly Polygon.io) flat files are daily gzipped CSVs served from an S3-compatible endpoint, https://files.massive.com, bucket flatfiles, and they are included from the $29 Starter tier on every asset class. What a plan can download depends on the dataset: day and minute aggregates come with Starter, tick-level trades with the $79 Developer tier, and quotes only with the $199 Advanced tier, which also unlocks the full archive (US stocks back to September 10, 2003). Each day's files are ready by about 11:00 ET the next morning. Every entitlement below was read from Massive's plan-access tables on 2026-10-11¹².

What are Massive flat files?

They are the bulk-history channel next to REST and WebSockets. Massive's quickstart describes them as "extensive historical market data as compressed CSVs over an S3-compatible endpoint", meant for when you need bulk history "without making thousands of REST calls"¹. Files are organized by asset class and data type, one file per trading day, each with a header row. Supported clients in the docs are the AWS CLI, rclone, MinIO and boto3¹.

Flat files use their own S3 access key and secret, issued in the Massive dashboard, separate from the REST API key¹.

Which plan includes which flat files?

US stocks, from the dataset pages' plan-access and plan-history tables²:

US stock records start on September 10, 2003, so "all history" means about 23 years². Options follow the same split on a shorter archive³:

What about indices, forex, crypto and futures?

Sources: the dataset pages for each product, read 2026-10-11⁴. The futures rows show CME; Massive publishes the same dataset families for CBOT, NYMEX and COMEX. On the business side, Stocks Business, Options Business, Indices Business, Currencies Business and the per-exchange Futures Business plans include the full archive²⁴.

How do I download them?

Point any S3 client at the Massive endpoint with your flat-file credentials¹:

aws configure set aws_access_key_id "$MASSIVE_S3_KEY"
aws configure set aws_secret_access_key "$MASSIVE_S3_SECRET"

aws s3 ls s3://flatfiles/us_stocks_sip/ --endpoint-url https://files.massive.com
aws s3 cp s3://flatfiles/us_stocks_sip/trades_v1/2025/11/2025-11-05.csv.gz . \
  --endpoint-url https://files.massive.com

The documented top-level prefixes are us_stocks_sip, us_options_opra, us_indices, global_forex and global_crypto; the trades example path shows the {dataset}_v1/YYYY/MM/YYYY-MM-DD.csv.gz layout¹. With boto3, pass endpoint_url="https://files.massive.com" and signature_version="s3v4"¹.

When do flat files beat REST?

When you need many symbols over many days. A minute-bar backfill of 5,000 tickers over a year is about 250 daily files, one request each, against thousands of paginated REST calls per symbol. Flat files also never count against a REST rate limit, which matters on the free tier's 5 calls per minute, though Basic has no flat-file access at all.

REST still wins for a handful of symbols, for today's data (files land the next morning around 11:00 ET) and for endpoints with no flat-file twin, such as reference data and fundamentals¹². A common pattern is flat files for the historical backfill, then REST or WebSockets for the current session. For resumable ingestion around either, see Rate-limited, resumable market-data ingestion.

What should I check before relying on them?

• Your plan's history window. Starter's 5-year window rolls forward; a backtest that needs 2015 data needs Developer (10 years) or Advanced.
• Quotes versus trades. NBBO quotes are Advanced-only for stocks and options; a spread-aware backtest cannot be built on Developer.
• Professional status. Individual Advanced plans are sold to non-professional users only; business plans cover firms⁵.
• Storage. Trades and quotes files are large; plan local storage and decompression before you start a multi-year pull.

Connects to

• Polygon.io Pricing 2026: the plan ladder these entitlements sit on.
• Polygon.io to Massive Migration 2026: moving from files.polygon.io and the polygon SDKs.
• Best Backtesting Data Sources 2026: flat files against other history sources.
• Data Vendor TCO: cost the plan you need.

References

Footnotes

1. Massive. "Flat Files Quickstart" (S3 endpoint https://files.massive.com, bucket flatfiles, prefixes, sample path, supported clients, separate S3 credentials, data available by about 11:00 AM ET the next day). Read 2026-10-11. https://massive.com/docs/flat-files/quickstart ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

2. Massive. "Flat Files: Stocks Trades" and sibling stocks dataset pages (plan access, recency, plan history; records from September 10, 2003). Read 2026-10-11. https://massive.com/docs/flat-files/stocks/trades ↩ ↩² ↩³ ↩⁴ ↩⁵

3. Massive. "Flat Files: Options Quotes" and sibling options dataset pages (records from June 2, 2014; quotes from March 7, 2022). Read 2026-10-11. https://massive.com/docs/flat-files/options/quotes ↩

4. Massive. Flat-file dataset pages for indices, forex, crypto and futures (CME trades, quotes, minute and session aggregates), listed in the docs index. Read 2026-10-11. https://massive.com/docs/llms.txt ↩ ↩²

5. Massive. "Pricing" (Starter $29, Developer $79, Advanced $199; Indices and Currencies ladders; non-professional restriction on Advanced). Read 2026-10-11. https://massive.com/pricing ↩

Frequently asked questions

Which Massive plan includes flat files?

Flat files start at the $29 Starter tier for stocks, options and futures, and at the $49 Starter tiers for indices and currencies. Stocks Starter gets day and minute aggregates for 5 years; trades need Developer ($79) and quotes need Advanced ($199). The free Basic tier has no flat files (read 2026-10-11).

What is the Massive flat files S3 endpoint?

https://files.massive.com with the bucket flatfiles. Use the S3 access key and secret from the Massive dashboard, not the REST API key. Prefixes include us_stocks_sip, us_options_opra, us_indices, global_forex and global_crypto.

How far back do Massive flat files go?

US stocks from September 10, 2003; options trades and aggregates from June 2, 2014 and options quotes from March 7, 2022; forex from September 25, 2009; crypto from November 1, 2013; CME futures from April 3, 2017; indices from February 14, 2023. Lower tiers see a rolling window of that archive.

When are Massive flat files updated?

Each trading day's files are available by about 11:00 AM ET the following day, according to Massive's flat-files quickstart. Use REST or WebSockets for the current session.