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Sionna Therapeutics, Inc.

SION
Exchange
Nasdaq
Industry
Pharmaceutical Preparations
SEC CIK
0002036042

In the last 90 days, Sionna Therapeutics, Inc. insiders filed 0 open-market purchases and 1 sale; 146 institutions reported holding it in 13F filings for Q2 2026, worth $2.11B in total; Viking Global Investors is the only superinvestor holding it.

Four kinds of short-selling data, each measuring something different:

  • Short interest: shares sold short and not yet bought back, as of a settlement date. FINRA publishes it twice a month, about eight business days after the settlement date.
  • Daily short volume: shares sold short each day in off-exchange trades reported to FINRA. It counts trades, not open positions, and is published the next day.
  • Fails-to-deliver: shares not delivered by the settlement date. The SEC publishes them twice a month, about two weeks late.
  • ATS (dark pool) volume: weekly volume on alternative trading systems and other off-exchange venues. FINRA publishes it two to four weeks after the week.

More in the glossary.

Short interest

Shares sold short and not yet bought back, from FINRA, on every settlement date in the last two years.

Short interest
4.21M
Shares, settlement Oct 30, 2026
Change
+535.7K
+14.6% vs. Oct 15, 2026
Days to cover
4.10
Short interest ÷ average daily volume
Average daily volume
1.03M
Shares, as reported by FINRA
Short interest by settlement date
Feb 14, 2025: 630,656 sharesFeb 28, 2025: 1,329,000 sharesMar 14, 2025: 1,739,754 sharesMar 31, 2025: 2,280,720 sharesApr 15, 2025: 2,291,588 sharesApr 30, 2025: 2,502,341 sharesMay 15, 2025: 2,587,312 sharesMay 30, 2025: 2,871,885 sharesJun 13, 2025: 2,827,394 sharesJun 30, 2025: 3,631,953 sharesJul 15, 2025: 3,530,059 sharesJul 31, 2025: 3,679,050 sharesAug 15, 2025: 3,600,368 sharesAug 29, 2025: 3,475,743 sharesSep 15, 2025: 3,771,820 sharesSep 30, 2025: 3,931,123 sharesOct 15, 2025: 3,372,058 sharesOct 31, 2025: 2,965,776 sharesNov 14, 2025: 2,973,430 sharesNov 28, 2025: 2,862,557 sharesDec 15, 2025: 2,876,610 sharesDec 31, 2025: 3,258,091 sharesJan 15, 2026: 3,053,667 sharesJan 30, 2026: 3,143,560 sharesFeb 13, 2026: 3,064,857 sharesFeb 27, 2026: 3,350,255 sharesMar 13, 2026: 3,544,166 sharesMar 31, 2026: 3,756,705 sharesApr 15, 2026: 3,799,971 sharesApr 30, 2026: 4,230,439 sharesMay 15, 2026: 4,740,815 sharesMay 29, 2026: 4,639,069 sharesJun 15, 2026: 4,996,300 sharesJun 30, 2026: 5,522,307 sharesJul 15, 2026: 5,257,277 sharesJul 31, 2026: 4,198,394 sharesAug 14, 2026: 4,247,834 sharesAug 31, 2026: 4,298,665 sharesSep 15, 2026: 3,966,138 sharesSep 30, 2026: 3,797,732 sharesOct 15, 2026: 3,676,508 sharesOct 30, 2026: 4,212,186 shares
Short interest in SION by settlement date
Settlement dateShort interestChangeChange %Avg. daily volumeDays to cover
Oct 30, 20264.21M+535.7K+14.6%1.03M4.10
Oct 15, 20263.68M−121.2K−3.2%983.1K3.74
Sep 30, 20263.80M−168.4K−4.3%1.65M2.30
Sep 15, 20263.97M−332.5K−7.7%1.28M3.10
Aug 31, 20264.30M+50.8K+1.2%1.64M2.62
Aug 14, 20264.25M+49.4K+1.2%7.35M1.00
Jul 31, 20264.20M−1.06M−20.1%618.0K6.79
Jul 15, 20265.26M−265.0K−4.8%456.8K11.51
Jun 30, 20265.52M+526.0K+10.5%544.4K10.14
Jun 15, 20265.00M+357.2K+7.7%360.2K13.87
May 29, 20264.64M−101.7K−2.2%319.2K14.53
May 15, 20264.74M+510.4K+12.1%421.4K11.25
Apr 30, 20264.23M+430.5K+11.3%455.4K9.29
Apr 15, 20263.80M+43.3K+1.2%446.3K8.51
Mar 31, 20263.76M+212.5K+6.0%332.8K11.29
Mar 13, 20263.54M+193.9K+5.8%287.3K12.34
Feb 27, 20263.35M+285.4K+9.3%143.4K23.36
Feb 13, 20263.06M−78.7K−2.5%407.2K7.53
Jan 30, 20263.14M+89.9K+2.9%231.9K13.55
Jan 15, 20263.05M−204.4K−6.3%312.3K9.78
Dec 31, 20253.26M+381.5K+13.3%384.5K8.47
Dec 15, 20252.88M+14.1K+0.5%289.4K9.94
Nov 28, 20252.86M−110.9K−3.7%266.3K10.75
Nov 14, 20252.97M+7.65K+0.3%194.7K15.27
Oct 31, 20252.97M−406.3K−12.1%364.6K8.13
Oct 15, 20253.37M−559.1K−14.2%299.6K11.25
Sep 30, 20253.93M+159.3K+4.2%330.6K11.89
Sep 15, 20253.77M+296.1K+8.5%306.3K12.31
Aug 29, 20253.48M−124.6K−3.5%197.6K17.59
Aug 15, 20253.60M−78.7K−2.1%174.7K20.61
Jul 31, 20253.68M+149.0K+4.2%144.9K25.39
Jul 15, 20253.53M−101.9K−2.8%159.5K22.13
Jun 30, 20253.63M+804.6K+28.5%355.4K10.22
Jun 13, 20252.83M−44.5K−1.6%138.6K20.41
May 30, 20252.87M+284.6K+11.0%117.8K24.39
May 15, 20252.59M+85.0K+3.4%173.9K14.88
Apr 30, 20252.50M+210.8K+9.2%108.1K23.14
Apr 15, 20252.29M+10.9K+0.5%180.5K12.69
Mar 31, 20252.28M+541.0K+31.1%272.2K8.38
Mar 14, 20251.74M+410.8K+30.9%201.3K8.64
Feb 28, 20251.33M+698.3K+110.7%199.9K6.65
Feb 14, 2025630.7K+630.7K+100.0%301.4K2.09

Fails-to-deliver

Shares that weren't delivered by the settlement date, from the SEC, for the last 30 dates with fails. The price is the previous day's closing price published by the SEC.

Fails-to-deliver in SION by settlement date
Settlement dateSharesPriceValue
Oct 5, 20262,445$4.91$12.0K
Oct 1, 2026271$5.26$1.43K
Sep 23, 20261,703$6.02$10.3K
Sep 16, 20261,765$6.88$12.1K
Sep 15, 2026338$8.26$2.79K
Sep 11, 202639,094$7.62$297.9K
Sep 9, 202618,174$7.30$132.7K
Sep 8, 202661,912$7.18$444.5K
Sep 3, 20266,233$7.31$45.6K
Sep 2, 20264,120$6.46$26.6K
Sep 1, 202669,585$6.03$419.6K
Aug 31, 202640,891$5.87$240.0K
Aug 26, 202699,175$6.25$619.8K
Aug 25, 202685,182$5.59$476.2K
Aug 24, 202690,445$5.29$478.5K
Aug 21, 202689,243$5.52$492.6K
Aug 20, 20268,179$6.25$51.1K
Aug 19, 2026700$5.94$4.16K
Aug 17, 20266,780$6.46$43.8K
Aug 14, 202613,771$6.54$90.1K
Aug 13, 20263,408$6.25$21.3K
Aug 12, 2026498$5.10$2.54K
Aug 11, 20262,315$4.50$10.4K
Aug 5, 20263$49.94$149.82
Aug 4, 20261$49.26$49.26
Aug 3, 202611$47.13$518.43
Jul 29, 20261,736$46.55$80.8K
Jul 16, 2026908$44.38$40.3K
Jul 7, 202613$43.12$560.56
Jul 6, 20263,753$43.99$165.1K

Daily short volume

Off-exchange short-sale volume, not short interest: shares sold short each day in trades reported to FINRA, for the last 30 trading days.

The short volume ratio isn't a sentiment gauge: market makers sell short to fill buy orders and to hedge, so short sales are usually about half of off-exchange volume.

Off-exchange short volume in SION by trade date
Trade dateShort volumeShort exemptOff-exchange volumeShort volume ratio
Nov 10, 2026110,33420,978345,28032.0%
Nov 9, 2026113,4521,228370,95530.6%
Nov 6, 2026228,4575,187393,55958.0%
Nov 5, 2026162,043285369,45443.9%
Nov 4, 202670,4890206,06534.2%
Nov 3, 2026154,5340360,47842.9%
Nov 2, 2026141,65825295,13648.0%
Oct 30, 202670,9060162,70643.6%
Oct 29, 202687,9530271,00332.5%
Oct 28, 2026117,1440282,65641.4%
Oct 27, 2026145,8325452,71532.2%
Oct 26, 2026154,7900286,83754.0%
Oct 23, 2026247,207100433,34857.0%
Oct 22, 2026287,7940546,96352.6%
Oct 21, 2026306,216300521,55558.7%
Oct 20, 2026142,8931420,27134.0%
Oct 19, 2026311,4660519,37960.0%
Oct 16, 2026410,07920617,96466.4%
Oct 15, 2026185,5744,833373,95849.6%
Oct 14, 2026379,9553,665728,33152.2%
Oct 13, 2026163,666263331,28049.4%
Oct 12, 2026111,6395271,86241.1%
Oct 9, 202683,0880184,83345.0%
Oct 8, 202672,0220201,04135.8%
Oct 7, 2026176,958121341,79351.8%
Oct 6, 2026284,4320650,98543.7%
Oct 5, 2026178,3860567,22231.4%
Oct 2, 2026207,327340475,17943.6%
Oct 1, 2026267,1980405,99565.8%
Sep 30, 2026238,1590407,94858.4%

ATS (dark pool) volume

Weekly volume on alternative trading systems (ATS) and other off-exchange (OTC) venues, from FINRA, for the last 12 weeks. ATS share is ATS volume ÷ (ATS + OTC volume), not a share of all trading.

Weekly ATS and OTC volume in SION
Week ofTierATS sharesATS tradesOther OTC sharesOther OTC tradesATS share
Oct 5, 2026T21,086,01815,842905,1804,05154.5%
Sep 28, 2026T21,179,25523,154832,6595,31158.6%
Sep 21, 2026T22,334,24728,6251,815,3807,10056.3%
Sep 14, 2026T22,225,90837,1861,700,7099,56756.7%
Sep 7, 2026T21,227,14124,307529,4813,99569.9%
Aug 31, 2026T21,525,16422,8841,141,8717,65457.2%
Aug 24, 2026T21,516,75521,5351,545,0657,90249.5%
Aug 17, 2026T22,061,50028,3933,032,04415,90740.5%
Aug 10, 2026T210,387,72798,87731,277,894129,85424.9%
Aug 3, 2026T21,352,10129,373431,5943,76475.8%
Jul 27, 2026T2617,67716,097133,9632,53682.2%
Jul 20, 2026T21,478,03123,683318,8434,48282.3%