Massive.com Python Client (formerly Polygon.io)

2.0.0 · active · verified Sun Apr 19

Official Python client for Massive.com (formerly Polygon.io) REST and WebSocket financial data APIs. Polygon.io rebranded as Massive.com on October 30, 2025. Package renamed from polygon-api-client. Import path changed from 'polygon' to 'massive'. Both api.polygon.io and api.massive.com remain operational. Current stable version follows the polygon-api-client release cadence.

Common errors

```
ImportError: cannot import name 'RESTClient' from 'polygon'
```
cause Using old import path after upgrading to massive-api-client v2.x.

fix Change 'from polygon import RESTClient' to 'from massive import RESTClient'.
```
ModuleNotFoundError: No module named 'massive'
```
cause Still using polygon-api-client v1.x or package not installed.

fix Run 'pip install massive-api-client' to get v2.x with the new import path.
```
401 Client Error: Unauthorized for url: https://api.massive.com
```
cause API key not passed or invalid.

fix Pass API key explicitly: RESTClient(api_key=os.environ['POLYGON_API_KEY']) or set POLYGON_API_KEY env var.

Warnings

breaking Import path changed from 'polygon' to 'massive' in v2.0.0. 'from polygon import RESTClient' no longer works with the new package.
Fix: Update imports to 'from massive import RESTClient' and 'from massive.websocket import WebSocketClient'.
breaking Default API base URL changed from api.polygon.io to api.massive.com in v2.0.0. Both domains remain operational.
Fix: If you must use the old endpoint explicitly: RESTClient(API_KEY, base_url='https://api.polygon.io')
gotcha Existing POLYGON_API_KEY values continue to work with Massive.com. No key rotation needed.
Fix: No action needed. Keep using your existing API key.

Install

pip install massive-api-client Install (new name)
pip install polygon-api-client Install (old name, still works)

Imports

RESTClient
wrong:
```
from polygon import RESTClient
```
correct:
```
from massive import RESTClient
```
Import path changed from 'polygon' to 'massive' in v2.0.0 as part of the Polygon.io → Massive.com rebrand. Old import still works if using polygon-api-client v1.x.

WebSocketClient

wrong:

from polygon.websocket import WebSocketClient

correct:

from massive.websocket import WebSocketClient

Quickstart

Both POLYGON_API_KEY and MASSIVE_API_KEY env vars work. Existing API keys continue to function after rebrand.

import os
from massive import RESTClient

API_KEY = os.environ.get('POLYGON_API_KEY') or os.environ.get('MASSIVE_API_KEY')

with RESTClient(API_KEY) as client:
    resp = client.get_aggs('AAPL', 1, 'day', '2024-01-01', '2024-01-10')
    for agg in resp.results:
        print(agg)

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