YORK CHARLES N II (COO, CFO and Secretary) sold 1.9% of their position (6.07K shares) of DAY ONE BIOPHARMACEUTICALS, INC. on the open market

Open‑market sale worth $70.4K — a minor trim. Review remaining holdings and any 10b5‑1 plan disclosures.

S · 1 sale

YORK CHARLES N II

Filed: 2/18/2026ACC: 0001655962-26-000004

InsiderYORK CHARLES N IICIK 1655962

→

IssuerDAY ONE BIOPHARMACEUTICALS, INC.CIK 1845337

Officer· COO, CFO and Secretary

Since May 2021

-6.07K

Net shares

Net seller

$70.4K

Total sold

Open market trades

0B · 1S

Total transactions

23.38K acquired · 29.44K disposed

Non-Derivative Transactions5

Common Stock

Direct

M · Option Exercise

+2.25K

Price / share

—

Trade value

—

% of position

0.8%

2/15/2026

294.71K→296.96K

Common Stock

Direct

M · Option Exercise

+6.63K

Price / share

—

Trade value

—

% of position

2.2%

2/15/2026

296.96K→303.59K

Common Stock

Direct

M · Option Exercise

+6.63K

Price / share

—

Trade value

—

% of position

2.2%

2/15/2026

303.59K→310.21K

Common Stock

Direct

M · Option Exercise

+7.88K

Price / share

—

Trade value

—

% of position

2.5%

2/15/2026

310.21K→318.09K

Common Stock

Direct

S · Sale

−6.07K

Price / share

$11.60

Trade value

$70.36K

% of position

1.9%

2/17/2026

318.09K→312.02K

Total

Net shares

+17.31K

Net value

-$70.36K

Security	Date	Type	Shares	Price / Share	Trade Value	% of Position	Held Before	Held After
Common Stock Direct	2/15/2026	M · Option Exercise	+2.25K	—	—	0.8%	294.71K	296.96K
Common Stock Direct	2/15/2026	M · Option Exercise	+6.63K	—	—	2.2%	296.96K	303.59K
Common Stock Direct	2/15/2026	M · Option Exercise	+6.63K	—	—	2.2%	303.59K	310.21K
Common Stock Direct	2/15/2026	M · Option Exercise	+7.88K	—	—	2.5%	310.21K	318.09K
Common Stock Direct	2/17/2026	S · Sale	−6.07K	$11.60	$70.36K	1.9%	318.09K	312.02K
Total			+17.31K		-$70.36K

Derivative Transactions4

Restricted Stock Unit (RSU)

Direct

M · Option Exercise

Converts to

Common Stock

2.25K shares

−2.25K

Strike price

Held after

6.75K

Exercisable

—

2/15/2026

Restricted Stock Unit (RSU)

Direct

M · Option Exercise

Converts to

Common Stock

6.63K shares

−6.63K

Strike price

Held after

46.38K

Exercisable

—

2/15/2026

Restricted Stock Unit (RSU)

Direct

M · Option Exercise

Converts to

Common Stock

6.63K shares

−6.63K

Strike price

Held after

72.88K

Exercisable

—

2/15/2026

Restricted Stock Unit (RSU)

Direct

M · Option Exercise

Converts to

Common Stock

7.88K shares

−7.88K

Strike price

Held after

118.13K

Exercisable

—

2/15/2026

Security	Converts To	Date	Type	Shares	Exercisable	Held After
Restricted Stock Unit (RSU) Direct	Common Stock2.25K shares	2/15/2026	M · Option Exercise	−2.25K	—	6.75K
Restricted Stock Unit (RSU) Direct	Common Stock6.63K shares	2/15/2026	M · Option Exercise	−6.63K	—	46.38K
Restricted Stock Unit (RSU) Direct	Common Stock6.63K shares	2/15/2026	M · Option Exercise	−6.63K	—	72.88K
Restricted Stock Unit (RSU) Direct	Common Stock7.88K shares	2/15/2026	M · Option Exercise	−7.88K	—	118.13K