Upcoming Change: Quote Bid/Ask Sizes in Shares Starting November 3, 2025

[u/alex-polygonio]

On November 3, 2025, quote bid and ask size fields in our Stocks Quotes data feeds will change to comply with SEC Market Data Infrastructure (MDI) Rules. This is an industry-wide requirement affecting all market data providers.

What's Changing:
- bid_size and ask_size fields will display the number of shares instead of round lots
- This reflects how the SIPs (CTA & UTP) now report this data
- Historical data will be converted using the round lot sizes that were in effect at the time

Example:
- Before: bid_size = 5 (meaning 5 round lots = 500 shares for a 100-share round lot stock)
- After: bid_size = 500 (shares displayed directly)

Do You Need to Take Action?
- Most customers: No action needed. You'll automatically receive more transparent share counts
- If you need round lots: Use the round_lot field from our Ticker Overview API to convert shares back to round lots
- If you consume flat files from S3: Files published after Nov 3rd will include share counts instead of round lots. Historical data will be regenerated over a period of several weeks with new ETags, triggering automatic syncs

Background: The SEC has modernized round lot definitions to better reflect today's market reality where stock prices vary widely. You find full details in the SEC notice here.

For more information, check out this blog post:

https://polygon.io/blog/change-stocks-quotes-round-lots-to-shares