The equity market structure is entering what Matt Billings, Vice President of Brokerage and President of Robinhood Financial & Robinhood Securities, called “the year of implementation”.
At SIFMA’s Market Structure Conference on November 20, the panel New Rules, New Rails: The Future of Equity Market Structure, moderated by Gregg E. Berman of Citadel Securities, revealed an industry committed to moving forward while genuinely unsure about which changes will ultimately stick.
Billings laid out the sheer scale of what’s coming. Round lot reform took effect in early November, replacing the traditional 100-share standard with a tiered system based on stock price, he said.
By early 2026, Trade Reporting Facilities will accept fractional trades, and the Securities Information Processors will post them with up to six decimal places. “That’s a big deal,” Billings said, though he acknowledged it doesn’t solve clearing and settlement challenges yet.
He said that the TRFs are pushing back their opening time from 8 AM to 4 AM, eliminating the overnight data dump; odd lots will be added to the SIP in the first half of 2026; Rule 605 disclosure reforms got pushed from December to August 2026; and the biggest changes, minimum trading increment reforms and excess fee caps, are scheduled for November 2026.
“The body of work here, of what is actually going to happen is immense,” Billings said.
But transparency comes at a cost, according to Ari Burstein, General Counsel and Chief Policy Officer, at Imperative Execution: ”When we have to implement some of these changes, go through system wide testing software changes internally, that’s taking away resources from other things like building products or improving products,” he said.
Burstein raised additional regulatory costs beyond the structural reforms, including CAT (the Consolidated Audit Trail) and Regulation SCI. “That is a huge cost for us, resources time as a small firm,” he said. “I wouldn’t forget about that when you add that to everything else that we’re going to have to do.”
Adrian Griffiths, Head of Market Structure, MEMX argued the industry may be undercounting implementation work. Beyond the technology changes, there’s extensive preparatory work through SIP operating committee meetings on how the consolidated tape will function in a 23-hour, 5-day trading environment, weekly meetings on extending investor protection regimes, and ongoing discussions about how Rule 605 reports will handle post-only and book-only order types.
“Saying we have one implementation per quarter, plus maybe one out there for 24/5, that’s probably under counting the amount of work that has to go into actually implementing all of these things,” he said.
Jessica D’Alton, Head of Americas Market Structure and Liquidity Strategy at UBS, emphasized the technology focus required. “I think the time that we’re spending on this is it’s meaningful. I think it’s driving our markets forward. I think these are all things that need to happen for us to get to that next point.”
The Uncertainty Factor
Beneath all this implementation work lies genuine uncertainty about whether these changes will proceed as planned. The new SEC administration’s focus on Order Protection Rule reform could reshape everything. Berman posed the uncomfortable question: if OPR reform eliminates protected quotes, what does it mean to put odd lots on the SIP and how do you distinguish an odd lot from a round lot if neither has protected quote status?
Burstein commented: “It would be great to know if all of these changes are going to happen, and if they’re not, then sooner than later, the better.” With the resources required, clarity on actual priorities would help enormously.
Jessica D’Alton, Head of Americas Market Structure and Liquidity Strategy, UBS, highlighted how interconnected everything is. If OPR gets repealed, routing practices need complete rethinking, she said: “It is kind of recreating our routing practices that exist today that are so clearly defined as having best price as best execution in a world where that’s not the baseline anymore.”
Griffiths added: “The order protection rule is very much the centerpiece of Reg NMS. And a lot of the other related rules are kind of offshoots of that.” Take access fees, they only exist because of OPR and technically only apply to accessing protected quotations, he said, adding that if OPR disappears, what happens to fee caps? “Do they disappear too, or get extended to cover lit ATSs, fundamentally changing competitive dynamics?” he questioned.
“What is the future end state for equity market structure, and what’s the right way to get there? Because we don’t want to see a situation where we’re implementing new rules and then pulling them back or modifying – that will be incredibly disruptive,” he said.
The conversation then shifted to the extended trading hours. “Everyone’s shrinking the down times with everything,” Billings said, adding that the SIPs and TRFs are working to support these hours, and DTCC continues shrinking its downtime. “This is really going in a positive way,” he said.
But institutional adoption remains uncertain. D’Alton said UBS is building capabilities because “it’s not an if, it’s more of a when,” driven partly by global clients wanting earlier US access. Still, nobody can predict what overnight liquidity will actually look like.
Eden Simmer, Executive Vice President, Head of Global Equity Trading, PIMCO, said: “If critical mass goes then my answer would be yes, we’re going to go where the volumes go.” But she raised real questions: Will brokers make risk overnight? What will spreads look like? “Is it a situation where this creates more liquidity in general, or are we just, you know, sort of dispersing liquidity over over a longer period of time?”
She also pointed out potential countervailing forces, like possible regulatory changes limiting earnings to twice yearly instead of quarterly—removing two major drivers of pre- and post-market volume spikes. “Just because you can, should you right?” she asked.
The panel revealed that modernization means different things to different firms. For institutional traders, it means preserving access to block liquidity, while adapting to new realities. For retail-focused firms, it means democratization and transparency. For venues, it means building infrastructure while managing regulatory uncertainty.
As D’Alton said: “The interconnectedness of it all playing together is going to be critical in how folks are responding to each one of these changes.”
