Stock Exchange Fixes Order Glitch and Typos Rulebook
Published Date: 12/8/2025
Notice
Summary
Nasdaq PHLX is updating its rules to say that the “Immediate-or-Cancel” time option can’t be used with Post-Only or Midpoint Peg Post-Only orders sent through the CORE FIX system. They also fixed a small mistake about when the “Trade Now” option is allowed for Midpoint Peg Post-Only orders. This change affects traders using these order types and is effective immediately, with no extra costs involved.
Analyzed Economic Effects
2 provisions identified: 0 benefits, 2 costs, 0 mixed.
IOC Not Allowed Via CORE FIX
If you submit Post-Only or Midpoint Peg Post-Only orders through the CORE FIX protocol, you cannot use the Immediate-or-Cancel (IOC) Time-in-Force and such orders will be rejected. The rule clarifies that IOC is unavailable via CORE FIX in addition to RASH and FIX. The change was filed on November 24, 2025 and will become operative 30 days after filing (on or about December 24, 2025); the Exchange expects CORE FIX functionality to be ready in the first quarter of 2026 and will announce implementation at least 30 days prior to going live.
Trade Now Removed for Midpoint Peg Post-Only
The 'Trade Now' order attribute is not available for Midpoint Peg Post-Only orders. The Exchange previously removed 'Trade Now' for that order type in 2024 but the rulebook online mistakenly showed it; the Exchange will remove the incorrect language from its rulebook 30 days after this filing (30 days after November 24, 2025, i.e., on or about December 24, 2025).
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