144 0002063775 XXXXXXXX LIVE 0001288847 Five9, Inc. 001-36383 3001 Bishop Dr. Suite 350 San Ramon CA 94583 925-201-2000 Bryan Lee Officer Common Morgan Stanley Smith Barney LLC

Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004

1835 48333.9 77262690 09/04/2025 Nasdaq Common 09/03/2025 RSU Issuer N 1835 09/03/2025 Not Applicable N Bryan Lee

3001 Bishop Dr. Suite 350 San Ramon CA 94583

Common 06/04/2025 1798 50847.44 The sale reported on this Form 144 represents an Issuermandated sale by the Reporting Person to cover taxwithholding obligations in connection with the vesting andsettlement of Restricted Stock Units, and it does notrepresent a discretionary trade by the Reporting Person. 09/03/2025 Bryan Lee