C4 Therapeutics heads into the week of May 11 with a striking divergence: short sellers are heavily dug in at more than a quarter of the free float, yet options traders are leaning bullish at a pace not seen in months.
The short position is the dominant feature of this setup. At roughly 26% of the free float — cross-confirmed by FINRA's April 30 fortnightly report at approximately 21 million shares — this is substantial bear conviction for a micro-cap biotech trading near $3.17. What makes the trajectory more notable is the pace of the build: short interest was around 17% of the float at the start of April and climbed sharply through the second half of the month, adding nearly nine percentage points in roughly three weeks. The position has since plateaued in the 26% range over the past fortnight. Days to cover come in near 11, meaning at average volume it would take more than two weeks to close the position. The ORTEX short score of 58.7 is elevated, ranking in roughly the 77th percentile of the universe.
The borrow market, however, tells a more relaxed story than the short level alone would imply. Cost to borrow is just 0.55% — barely above flat, and down around 9% on the week, even though it has risen about 38% over the past month. Availability remains wide open: the lending pool shows only around 2.7% of available shares currently lent out, against a 52-week utilization high of 80.5%. There is no squeeze pressure in the borrow market. Whoever is short has no imminent difficulty maintaining the position.
Options positioning cuts the other direction entirely. The put/call ratio has fallen to 0.22 — well below its 20-day average of 0.29 and running about 1.4 standard deviations beneath it. That makes this one of the more call-heavy readings of the past year (52-week low is 0.03, high is 0.57). Call buyers have dominated for most of May after a more balanced April, suggesting at least one cohort of market participants sees upside from the current $3.17 level despite the heavy short interest overhead.
The analyst picture is constructive in direction but the most recent changes are now roughly 76 days stale, which limits their value as a live signal. The last actions on record, from late February, saw Barclays lift its target to $7 while maintaining Overweight, and Brookline Capital raise to $30 — a number that appears out of step with the rest of the coverage universe and the current stock price, so that figure is best set aside. The broader consensus centres on Overweight and Buy ratings from Barclays, Wells Fargo, Guggenheim, and TD Cowen. The bull case rests on cemsidomide's 34% overall response rate in relapsed/refractory multiple myeloma, which compares favourably to a comparable competitor at 25%. The bear case points to pricing risks from the Inflation Reduction Act and the clinical risks inherent in targeting difficult-to-drug pathways. The price/book ratio of 5.5x has expanded meaningfully over the past month — consistent with a stock up 25% in one month — while PE and earnings yield multiples are deeply negative, reflecting that the company is pre-profitability.
Institutional ownership adds some context to the directional tug-of-war. Point72 added roughly 9.3 million shares in the period ending December 2025, making it the largest disclosed holder at 8.6% of shares outstanding. RA Capital entered with 8 million shares — a new position — in the same period. Bain Capital Life Sciences added 6 million shares. These are specialist healthcare investors taking material stakes, which partly explains why the cost to borrow remains low despite a 26% short interest level: the register is anchored by long-only biotech specialists who are not lending their shares cheaply or at all. Vanguard and BlackRock have both been adding more recently, with BlackRock last reporting through April 30.
The next confirmed earnings event is June 24. The most recent prints have delivered meaningful moves: in February, the stock rose 14% on the day following results and extended to nearly 9.4% on the five-day view. With short interest near the top of its recent range and call buyers already positioned for a move higher, the lead-up to that date is worth watching closely.
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