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The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell and are not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

Filed pursuant to Rule 424(b)(5)

Registration No. 333-277609

SUBJECT TO COMPLETION, DATED SEPTEMBER 10, 2026

PRELIMINARY PROSPECTUS SUPPLEMENT
(To Prospectus Dated August 19, 2026)

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Shares of Common Stock

Pre-funded Warrants to Purchase Shares of Common Stock

We are offering shares of our common stock and, in lieu of common stock to certain investors that so choose, pre-funded warrants to purchase shares of our common stock. The purchase price of each pre-funded warrant will equal the price per share at which shares of our common stock are being sold to the public in this offering, minus $0.0001 per share of common stock, the exercise price of each pre-funded warrant. The public offering price for each share of common stock is $ . We are also offering the shares of our common stock that are issuable from time to time upon exercise of the pre-funded warrants. Our common stock trades on the Nasdaq Capital Market (“Nasdaq”) under the symbol “YARW.” On September 9, 2026, the last reported sale price for our common stock on Nasdaq was $29.11 per share.

There is no established public trading market for the pre-funded warrants, and we do not expect a market to develop. We do not intend to apply for listing of the pre-funded warrants on Nasdaq or any securities exchange or nationally recognized trading system. Without an active trading market, the liquidity of the pre-funded warrants will be limited.

Investing in our securities involves risks. See the section titled “Risk Factors” beginning on page S-6 of this prospectus supplement and page 4 of the accompanying prospectus, as well as in the documents incorporated by reference herein and therein, to read about factors you should consider before buying our securities.

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved these securities, or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

PER SHARE

PER
PRE-FUNDED
WARRANT

TOTAL

Public Offering Price

Underwriting Discounts and Commissions(1)

Proceeds, Before Expenses, to Yarrow Bioscience, Inc.

(1)

See the section titled “Underwriting” for additional information regarding underwriting compensation.

Delivery of the shares of common stock and pre-funded warrants is expected to be made on or about , 2026.

We have granted the underwriters an option for a period of 30 days to purchase up to an additional shares of our common stock. If the underwriters exercise the option in full, the total underwriting discounts and commissions payable by us will be $ and the total proceeds to us, before expenses, will be $ .

Joint Book-Running Managers

Jefferies

TD Cowen

Guggenheim Securities

Lead Manager

LifeSci Capital

Prospectus supplement, dated , 2026

	Page
ABOUT THIS PROSPECTUS SUPPLEMENT		S-1
PROSPECTUS SUPPLEMENT SUMMARY		S-2
THE OFFERING		S-4
RISK FACTORS		S-6
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		S-9
USE OF PROCEEDS		S-11
DILUTION		S-12
DESCRIPTION OF SECURITIES WE ARE OFFERING		S-14
U.S. FEDERAL INCOME TAX CONSIDERATIONS		S-16
UNDERWRITING		S-21
LEGAL MATTERS		S-30
EXPERTS		S-31
WHERE YOU CAN FIND MORE INFORMATION		S-32
INCORPORATION BY REFERENCE		S-33

	Page
ABOUT THIS PROSPECTUS		ii
SUMMARY		1
RISK FACTORS		4
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		5
USE OF PROCEEDS		7
SECURITIES WE MAY OFFER		8
PLAN OF DISTRIBUTION		14
LEGAL MATTERS		17
EXPERTS		17
WHERE YOU CAN FIND MORE INFORMATION		18
INCORPORATION BY REFERENCE		19

Public offering price per share			$
Pro forma net tangible book value per share as of June 30, 2026	$	39.92
Increase in pro forma net tangible book value per share attributable to this offering	$
As adjusted pro forma net tangible book value per share immediately after this offering			$
Dilution in pro forma net tangible book value per share to new investors in this offering			$