Polygon.io to Massive Migration 2026: API, SDKs, Keys

Moving code from Polygon.io to Massive takes four changes: point REST calls at api.massive.com, WebSockets at socket.massive.com (or delayed.massive.com), flat-file downloads at files.massive.com, and swap the polygon SDK for the massive package. Your API key, account and plan do not change. Polygon.io became Massive on October 30, 2025, and Massive says api.polygon.io keeps working "for an extended period", with a phase-out to be announced with notice¹. Every host, package and version below was checked against Massive's docs, its GitHub READMEs and the package registries on 2026-10-11.

What changed when Polygon.io became Massive?

The brand, the domains and the SDK names. Massive's announcement lists what stayed the same: existing code, keys and logins remain valid, REST, WebSocket and flat-file products are unchanged, and polygon.io pages redirect to massive.com¹. What changed: a new primary API base at api.massive.com, emails moving to @massive.com, invoices and card statements showing Massive.com, Inc., and new branded SDKs that default to the new base¹.

Plans were reworked separately from the rename. The current ladder (free Basic with end-of-day data, $29 Starter with WebSockets and flat files, $79 Developer with trades, $199 Advanced with quotes and real-time data) is covered in Polygon.io Pricing 2026.

Which hostnames do I change?

The rebrand notice commits only to api.polygon.io by name¹. The WebSocket and flat-file docs now list only massive.com hosts²³, so treat the other polygon.io hostnames as legacy and move them in the same change.

Which SDK package replaces the Polygon client?

Versions are the latest on PyPI and npm on 2026-10-11⁵⁶. Massive's READMEs say the new SDKs default to api.massive.com and that only minor changes such as imports are needed⁴⁷. The old packages have had no release since the rebrand, so bug fixes and new endpoints land in the massive packages only.

What does the Python change look like?

# before
# pip install polygon-api-client
# from polygon import RESTClient

# after
# pip install -U massive
import os
from massive import RESTClient

client = RESTClient(api_key=os.environ["MASSIVE_API_KEY"])
for bar in client.list_aggs(ticker="AAPL", multiplier=1, timespan="day",
                            from_="2026-09-01", to="2026-09-30", limit=50000):
    print(bar.timestamp, bar.close)

The method names (list_aggs, get_last_trade, list_trades, list_snapshot_options_chain) are the ones in the massive README⁴. Massive's own guidance for agents is to keep the key in a MASSIVE_API_KEY environment variable rather than in code or chat⁸.

How do raw HTTP calls authenticate?

Two ways, unchanged from the Polygon era: an apiKey query parameter, or an Authorization: Bearer header⁹.

curl -H "Authorization: Bearer $MASSIVE_API_KEY" \
  "https://api.massive.com/v2/aggs/ticker/AAPL/range/1/day/2026-09-01/2026-09-30"

Prefer the header: query-string keys end up in proxy and server logs. Responses keep the familiar envelope with status, request_id, results and, for paginated endpoints, next_url⁹.

What changes for WebSocket clients?

Only the host, if you already authenticate by message. Connect to the feed your plan includes, send {"action":"auth","params":"YOUR_API_KEY"}, wait for auth_success, then subscribe with channel prefixes such as T. for trades². Massive's quickstart notes a default of one concurrent WebSocket connection per asset class; a second connection for the same asset class needs a request to support¹⁰. Workers that each open their own socket should share one connection and fan out internally.

What changes for flat-file downloads?

The S3 endpoint and bucket: https://files.massive.com, bucket flatfiles, with prefixes such as us_stocks_sip, us_options_opra, us_indices, global_forex and global_crypto³. Flat files use their own S3 access key and secret from the dashboard, not your REST key³.

aws s3 ls s3://flatfiles/us_stocks_sip/ --endpoint-url https://files.massive.com

Which datasets each plan can download is laid out in Massive Flat Files 2026.

What should a migration checklist cover?

1. Replace api.polygon.io with api.massive.com in config, not in scattered string literals.
2. Move WebSocket URLs to socket.massive.com or delayed.massive.com and confirm your plan's feed.
3. Move flat-file jobs to files.massive.com and rotate the S3 credentials into your secret store.
4. Swap SDK packages and fix imports; pin versions in lockfiles.
5. Rename the environment variable to MASSIVE_API_KEY so logs and runbooks match current docs.
6. Allow massive.com and api.massive.com in egress firewalls and CSP rules before cutting over.
7. Re-run integration tests against the new hosts; the key itself does not change.

If an agent is the consumer, Massive also offers a hosted MCP server and per-request x402 access; see Massive for AI Agents 2026.

Connects to

• Polygon.io Pricing 2026: the current plan ladder.
• Massive Flat Files 2026: bulk downloads by plan.
• Polygon.io Free Tier Limits 2026: what a free key can do.
• Rate-limited, resumable market-data ingestion: ingestion patterns that survive a host change.

References

Footnotes

1. Massive. "Polygon.io is Now Massive" (October 30, 2025; api.massive.com in parallel with api.polygon.io; keys and logins unchanged; phase-out of old endpoints to be announced with notice). Read 2026-10-11. https://massive.com/blog/polygon-is-now-massive ↩ ↩² ↩³ ↩⁴ ↩⁵

2. Massive. "WebSocket: Stocks Trades" (delayed feed wss://delayed.massive.com/stocks, real-time wss://socket.massive.com/stocks; auth message; T. channel). Read 2026-10-11. https://massive.com/docs/websocket/stocks/trades ↩ ↩² ↩³ ↩⁴

3. Massive. "Flat Files Quickstart" (endpoint https://files.massive.com, bucket flatfiles, prefixes, S3 keys from the dashboard). Read 2026-10-11. https://massive.com/docs/flat-files/quickstart ↩ ↩² ↩³ ↩⁴

4. Massive. "Massive (formerly Polygon.io) Python Client" README (pip install -U massive; RESTClient and WebSocketClient; default base api.massive.com). Read 2026-10-11. https://github.com/massive-com/client-python ↩ ↩² ↩³

5. PyPI. "massive" (2.8.0) and "polygon-api-client" (1.16.3, uploaded 2025-10-30). Read 2026-10-11. https://pypi.org/project/massive/ ↩

6. npm. "@massive.com/client-js" (10.8.0) and "@polygon.io/client-js" (8.2.0, 2025-08-13). Read 2026-10-11. https://www.npmjs.com/package/@massive.com/client-js ↩

7. Massive. "Massive JS Client" README (npm install @massive.com/client-js; restClient(process.env.MASSIVE_API_KEY)). Read 2026-10-11. https://github.com/massive-com/client-js ↩

8. Massive. "llms.txt" documentation index (store the key in MASSIVE_API_KEY; key at massive.com/dashboard/keys). Read 2026-10-11. https://massive.com/docs/llms.txt ↩

9. Massive. "REST Quickstart" (apiKey query parameter or Authorization Bearer header; response envelope). Read 2026-10-11. https://massive.com/docs/rest/quickstart ↩ ↩²

10. Massive. "WebSocket Quickstart" (one concurrent WebSocket connection per asset class by default). Read 2026-10-11. https://massive.com/docs/websocket/quickstart ↩

Frequently asked questions

Do I need a new API key after the Polygon.io to Massive rebrand?

No. Massive's October 30, 2025 announcement says existing keys, accounts and logins remain valid. Keys are now managed at massive.com/dashboard/keys, but the key value works against both api.polygon.io and api.massive.com.

Does api.polygon.io still work in 2026?

Massive said at the rebrand that api.polygon.io continues to work for an extended period and that it would give notice before phasing out the old endpoints. Its current SDKs default to api.massive.com, so new code should use the new base.

What is the Python package for Massive?

pip install -U massive, then from massive import RESTClient (2.8.0 on PyPI as of 2026-10-11). The old polygon-api-client package has had no release since 1.16.3 on 2025-10-30.

What are the Massive WebSocket and flat-file hosts?

WebSockets connect to wss://socket.massive.com/{asset} for real-time or wss://delayed.massive.com/{asset} for delayed data. Flat files are an S3-compatible endpoint at https://files.massive.com with the bucket flatfiles and separate S3 credentials.