Casdin Partners Master Fund's recent Form 4 filings paint a picture of a manager running in two directions at once. Across 42 reported transactions in just two tickers, the fund recorded open-market purchases of roughly $22.1 million against open-market sales of $73.4 million. That sell-side figure is driven almost entirely by block disposals of BioLife Solutions (BLFS): a $21.4 million sale on October 15, 2025, followed by $6.8 million, $5.9 million, and $15.4 million sales on May 19, 20, and 21, 2026, respectively. The buy-side activity, by contrast, is concentrated in Standard BioTools (LAB), where 21 of the fund's 25 most recent trades were open-market purchases of that single ticker.
LAB accumulation ran from late August 2025 through early December 2025 in a steady, stepped pattern. Most of the buys were modest—ranging from roughly $108,000 to $586,000—but Casdin stepped up on November 25, 2025, with a single $9.8 million purchase. Smaller buys clustered through mid-November, including $541,395 on November 13 and $445,838 on November 12, while September and August saw a handful of low-six-figure additions. Across all reporting codes, the fund also showed $131.1 million in total acquired value, a figure that includes non-discretionary events such as grants and option exercises alongside the open-market buys.
The most recent direction, however, has shifted to the sell side. The three May 2026 BLFS sales alone total $28.1 million, and the last LAB purchase occurred on December 4, 2025, a $217,020 buy. In aggregate, the fund remains a net seller in dollar terms due to the much larger BLFS exits, but the transaction count reveals a clear buy bias in LAB throughout the second half of 2025.
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