Starting November 3, 2025, the SEC’s final rule will implement new definitions for “Round Lot” information under the Market Data Infrastructure Rules, enhancing transparency for investors and market participants regarding quotes and orders in NMS stocks. The new Round Lot rules involve specific tier designations. For more details, refer to the SEC Notice.

Currently, bid/ask size fields in Quote events reflect the number of lots. Going forward, they will represent the number of shares for a symbol rounded down to the nearest multiple of its Round Lot Size. Information regarding the lot size will be transmitted by dxFeed in a new field, ROUND_LOT_SIZE, within Instrument Profile File (IPF).

This change will impact clients receiving CTA/UTP data feeds.

Technical Details

Primarily, a round lot means 100 shares or multiples (e.g., 200, 1000, 5000). Some securities trade in round-lot sizes other than 100, like 1, 10, 25, or 50 shares.

Starting November 3, 2025 Best Bid Size will be the number of shares for a symbol, rounded down to the nearest multiple of its Round Lot Size. For example, if a symbol has a round-lot size of 40, potential sizes are 40, 80, 120, etc.

We’re also introducing a new field, ROUND_LOT_SIZE, to Instrument Profile File (IPF).

Effective date

Starting November 3, 2025, the bid/ask size fields in Quote events for CTA/UTP feeds will represent the number of shares for a symbol, rounded down to the nearest multiple of its Round Lot Size.

 

Please refer to dxFeed Help Desk if you have any questions or concerns.