Short Report: C3.AI short positioning at 2025-high

Welcome to this week’s installment of “The Short Interest Report” – The Fly’s weekly recap of short interest trends among some of the most widely followed high-short-float stocks. Using the data from our partner Ortex.com, which utilizes the latest information from stock lenders to estimate short interest changes for thousands of publicly traded companies, this report will screen for some of biggest changes in short interest as a percentage of free float and days-to-cover ratios while also considering the short interest data on some of the more volatile and heavier-traded names of the week. Based on the availability of data from Ortex, the report tracks the trading period that covers prior Friday through Thursday of this week, excluding holidays. As a basis of comparison for stocks discussed below, the S&P 500 index was up 2.1%, the Nasdaq Composite was up 2.9%, the Russell 2000 index was up 4.6%, the Russell 2000 Growth ETF (IWO) was up 4.4%, and the Russell 2000 Value ETF (IWN) was up 4.7% in the five-day trading session range through August 28.

SHORT INTEREST GAINERS

• A negative pre-announcement sending shares of C3.AI (AI) sharply lower also catalyzed a rush into bearish positioning, with Ortex-reported short interest on the name now up for the third consecutive week. Last week, the rise in shorts as a percentage of free float was especially acute, jumping from 22.5% to 27.0% – the highest level since September of 2024. As the spike in trading volume has subsided, days-to-cover on the name has also been lifted from 4.6 to 5.3 – the highest since the first week of June. The stock was up 2.7% in the five-day period covered, though share of C3.AI are still down about 22% relative to levels ahead of the pre-announcement and also down 51% year-to-date.
• Ortex-reported short interest data on Tempus AI (TEM) saw a reversal in the trend of two consecutive declining weeks against a post-earnings bounce in the stock price. Shorts as a percentage of free float rose from 20.9% to 24.1% – a record-high in bearish positioning also seen on July 24th and August 8th – just before that positive Q2 announcement. The stock fell 4% in the five-day period covered, though shares are still up 29% relative to pre-earnings levels and also up a whopping 125% year-to-date.
• Going into the company’s Q2 earnings on August 5, Ortex-reported short interest on Upstart (UPST) troughed at a four-month low of 21.5% in the final week of July, with a near-tripling in the stock price relative to Liberation Day Apil 2nd having shaken out some of the more conflicted bearish hands. Investors were unenthused by the company’s earnings however, sending shares down nearly 20% the session after results and paving the way for renewed bearish expression. This week, shorts as a percentage of free float for Upstart was up from 24.5% to 27.3% – the highest level since early July, though days-to-cover slipped from 4.3 to 4.2. The stock was also up about 16% in the five-day period covered but remains down 16% from July 31st highs.
• Ortex-reported short interest in ARS Pharmaceuticals (SPRY) troughed at 2025 low of 25.7% just three weeks ago but has since shot higher, with this week’s increase accelerating from 27.8% to a 12-week high of 34.8%. The stock had also nearly doubled from its early March lows by late July, though investors were unenthused by the company’s Q2 results and headed for the exits. Shares are down about 23% since reporting earnings on August 13, falling 13.5% in the five-day period covered through Thursday.

SHORT INTEREST DECLINERS

• Ortex-reported short interest in Sionna Therapeutics (SION) cratered last week as bears were squeezed out of their positions by the stock’s sharp post-earnings rally. Shorts as a percentage of free float fell from 32.1% all the way down to 21.5%, the lowest level since mid-June. Likewise, days-to-cover on the name are down from 27.7 to 12.9 – a four-month low. In the five-day period covered through Thursday, Sionna was up 8.3%, and the stock has now gained 45% from levels heading into Q2, when the management also signaled that it is preparing to advance its SION-719 drug into a Phase 2a proof-of-concept trial. Year-to-date however, Sionna Therapeutics is down about 2% from its February IPO price.