DUBOW ADAM (Gen Counsel & Secretary) sold 6.5% of their position (4.32K shares) of DAY ONE BIOPHARMACEUTICALS, INC. on the open market

Open‑market sale worth $38.5K — a moderate reduction. Review remaining holdings and any 10b5‑1 plan disclosures.

S · 1 sale

DUBOW ADAM

Filed: 11/18/2025ACC: 0001744507-25-000006

InsiderDUBOW ADAMCIK 1744507

→

IssuerDAY ONE BIOPHARMACEUTICALS, INC.CIK 1845337

Officer· Gen Counsel & Secretary

Since Feb 2026

-4.32K

Net shares

Net seller

$38.5K

Total sold

Open market trades

0B · 1S

Total transactions

12.09K acquired · 16.41K disposed

Non-Derivative Transactions5

Common Stock

Direct

M · Option Exercise

+2.96K

Price / share

—

Trade value

—

% of position

5.4%

11/15/2025

54.86K→57.82K

Common Stock

Direct

M · Option Exercise

+1.75K

Price / share

—

Trade value

—

% of position

3.0%

11/15/2025

57.82K→59.57K

Common Stock

Direct

M · Option Exercise

+3.69K

Price / share

—

Trade value

—

% of position

6.2%

11/15/2025

59.57K→63.26K

Common Stock

Direct

M · Option Exercise

+3.69K

Price / share

—

Trade value

—

% of position

5.8%

11/15/2025

63.26K→66.94K

Common Stock

Direct

S · Sale

−4.32K

Price / share

$8.91

Trade value

$38.50K

% of position

6.5%

11/17/2025

66.94K→62.63K

Total

Net shares

+7.77K

Net value

-$38.50K

Security	Date	Type	Shares	Price / Share	Trade Value	% of Position	Held Before	Held After
Common Stock Direct	11/15/2025	M · Option Exercise	+2.96K	—	—	5.4%	54.86K	57.82K
Common Stock Direct	11/15/2025	M · Option Exercise	+1.75K	—	—	3.0%	57.82K	59.57K
Common Stock Direct	11/15/2025	M · Option Exercise	+3.69K	—	—	6.2%	59.57K	63.26K
Common Stock Direct	11/15/2025	M · Option Exercise	+3.69K	—	—	5.8%	63.26K	66.94K
Common Stock Direct	11/17/2025	S · Sale	−4.32K	$8.91	$38.50K	6.5%	66.94K	62.63K
Total			+7.77K		-$38.50K

Derivative Transactions4

Restricted Stock Unit (RSU)

Direct

M · Option Exercise

Converts to

Common Stock

2.96K shares

−2.96K

Strike price

Held after

11.85K

Exercisable

—

11/15/2025

Restricted Stock Unit (RSU)

Direct

M · Option Exercise

Converts to

Common Stock

1.75K shares

−1.75K

Strike price

Held after

Exercisable

—

11/15/2025

Restricted Stock Unit (RSU)

Direct

M · Option Exercise

Converts to

Common Stock

3.69K shares

−3.69K

Strike price

Held after

29.50K

Exercisable

—

11/15/2025

Restricted Stock Unit (RSU)

Direct

M · Option Exercise

Converts to

Common Stock

3.69K shares

−3.69K

Strike price

Held after

44.25K

Exercisable

—

11/15/2025

Security	Converts To	Date	Type	Shares	Exercisable	Held After
Restricted Stock Unit (RSU) Direct	Common Stock2.96K shares	11/15/2025	M · Option Exercise	−2.96K	—	11.85K
Restricted Stock Unit (RSU) Direct	Common Stock1.75K shares	11/15/2025	M · Option Exercise	−1.75K	—	7K
Restricted Stock Unit (RSU) Direct	Common Stock3.69K shares	11/15/2025	M · Option Exercise	−3.69K	—	29.50K
Restricted Stock Unit (RSU) Direct	Common Stock3.69K shares	11/15/2025	M · Option Exercise	−3.69K	—	44.25K