MIAX Shorts Up 22% in a Month, Options Calm Before Tomorrow's Print

MIAX reports Q3 results after the close tomorrow with short interest running at its highest level in months, even as options traders show little sign of concern.

Short sellers have added roughly 22% to their positions over the past month, lifting the SI to 9.95% of free float, around 8.1 million shares. That is a material build for an exchange operator of this size. Yet the borrow market tells a different story: cost to borrow is just 0.45%, one of the lowest readings in the past six weeks, and availability is at 615%, meaning lenders are sitting on roughly six shares available to borrow for every share already shorted. The lending pool is loose. Whatever is driving the short build, it is not a crowded or expensive trade to carry, and there is no squeeze pressure in the market.

Options positioning is similarly relaxed. The put/call ratio is running at 0.50, barely a tenth of a standard deviation above its 20-day average of 0.50, and well below the 52-week high of 1.16 seen earlier this year. That is not the setup of a market preparing for a sharp move in either direction.

The analyst picture is more divided. Rosenblatt trimmed its target to $60 from $62 yesterday while keeping its Buy, and Morgan Stanley cut to $43 from $50 earlier this month while staying at Equal-Weight. The consensus mean sits at $45.80 against a current price of $32.53, implying roughly 41% upside on paper, though the range between Rosenblatt's $60 and Morgan Stanley's $43 reflects a genuine disagreement about trajectory. The bull case rests on compounding options market share: OCC data reportedly showed MIAX at 17.4% of the market in Q3 with 11.1 million average daily contracts, even as the broader market contracted 4% quarter over quarter. Q2 adjusted EBITDA rose 57% year on year, with margins reaching 54%. Bears point to dependence on volatile trading volumes and the structural pressure from CBOE, NYSE, and Nasdaq, which have resources MIAX cannot match. The EV/EBITDA multiple near 9.6x is not an obvious bargain for a business in this competitive position, but it is also not stretched by the standards of smaller exchange operators with genuine share-gain stories.

Insider activity on ORTEX's first-party SEC EDGAR data is all pre-arranged plan selling. The EVP and General Counsel, the CIO, and the Chief Strategy Officer have all sold shares under 10b5-1 plans over the past six weeks, with net insider activity amounting to roughly $24.4 million of net sales over 90 days. None of the trades appear to be discretionary; all are plan-driven, which limits the signal they carry. More interesting is the activist register: both Thomas Gallagher (Chairman and CEO) and Horizon Kinetics Asset Management hold 13D filings on the stock, making them the highest-profile investors in MIAX with active activist registrations. Horizon Kinetics has trimmed its stake from 12.2% to 7.8% since its first filing in August 2025, while Gallagher's stake slipped just below the 5% disclosure threshold as of his last filing in August 2025. As always with 13D/G positions, these are as-last-disclosed around the 5% threshold, and a holder can drop below without filing again. Retail attention spiked sharply ahead of the print: an ORTEX alt-data signal tracking Wikipedia views and ORTEX page traffic registered a z-score of 4.9 on October 23, unusually high relative to the company's own 90-day history.

The print will test whether the Q3 market share and volume data justify the recovery in adjusted EBITDA margins that the bull case requires, at a valuation that leaves modest room for disappointment and a short base that has been building steadily for four weeks.