From the U.S. Postal Service announcement on November 17, 2020:From the USPS: This Happy Birthday stamp conveys exuberant greetings by calling to mind the childhood excitement of a birthday party. Each of the five letters in the word “HAPPY” is inspired by a different party decoration in the midst of a flurry of multicolored ribbons and confetti. This stamp was designed by Lisa Catalone Castro and Rodolfo Castro, featuring a digital illustration by the latter. Ethel Kessler served as art director.

This stamp will be issued September 9th in Toast, N.C., but without a first-day ceremony.

The Scott catalogue number for this issue is 5635.

Additional information will be posted below the line, with the most recent at the top.

Updated August 25th:
Here are the first-day postmarks for this issue:The Digital Color Postmark measures 2.54″ x 1.45″The pictorial postmark measures 2.39″ x 1.15″

Updated July 30th from the Postal Bulletin:

On September 9, 2021, in Toast, NC, the United States Postal Service® will issue the Happy Birthday stamp (Forever® priced at the First-Class Mail® rate) in one design, in a pressure-sensitive adhesive (PSA) pane of 20 stamps (Item 577700). This stamp will go on sale nationwide September 9, 2021, and must not be sold or canceled before the first-day-of-issue.

This Happy Birthday stamp conveys exuberant greetings by calling to mind the childhood excitement of a birthday party. Each of the five letters in the word “HAPPY” is inspired by a different party decoration in the midst of a flurry of multicolored ribbons and confetti. Featuring a digital illustration by Rodolfo Castro, this stamp was designed by Lisa Catalone Castro and Rodolfo Castro. Ethel Kessler served as art director.