From the U.S. Postal Service announcement on October 22, 2019:

In 2020, the Postal Service issues Let’s Celebrate!, a new stamp that adds fun to celebratory greeting cards, invitations and gift-bearing envelopes and packages. No matter the occasion — birthday, anniversary, holiday, engagement, new job, retirement — Let’s Celebrate! helps send cheer along with well wishes. The stamp features an array of colorful circles in varying sizes arranged in a random pattern. The letters in the word “celebrate,” cast in a dark green hue, appear inside several brightly colored circles on a white background. Art director Antonio Alcalá designed the stamp.

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

This stamp will be issued Friday, February 14th, in Mesa, Arizona. That coincides with the ARIPEX stamp show in Mesa.

The Scott catalogue number is 5434.

January 21st: The “killerbar” postmark is also available for this issue, similar to this mock-up: The other two first-day postmarks are shown below.

Updated January 19:
[press release]
A New Stamp to Celebrate
U.S. Postal Service Says “Let’s Celebrate!” with Forever Stamp

What: In February 2020, the U.S. Postal Service will issue the Let’s Celebrate! stamp for any joyous occasion. Whether celebrating a birthday, an anniversary, a new job or retirement, this stamp will help mark the occasion.

News of the stamp is being shared with the hashtag #CelebrationStamp.

Who: Janice Walker, vice president, Corporate Communications, U.S. Postal Service

When: Friday, Feb. 14, 2020, 1 p.m. Mountain Time

Where: Aripex 2020 Stamp Show
Mesa Convention Center
263 North Center Street
Mesa, AZ 85201-6628

RSVP: Dedication ceremony attendees are encouraged to RSVP atusps.com/celebrationstamps

Background:.

Like a burst of confetti, Let’s Celebrate! adds an extra dash of color to celebratory greeting cards, invitations and gift-bearing envelopes and packages.

The Let’s Celebrate! stamp features colorful circles in varying sizes arranged in a random pattern. The letters in “celebrate,” cast in a dark green hue, appear inside several brightly colored circles. Art director Antonio Alcalá designed the stamp.

Let’s Celebrate! is being issued as a Forever stamp, which will always be equal in value to the current First-Class Mail 1-ounce price.

Updated January 2 from the Postal Bulletin:

On February 14, 2020, in Mesa, AZ, the United States Postal Service will issue the Let’s Celebrate! stamp (Forever priced at the First-Class Mail rate) in one design, in a pressure-sensitive adhesive (PSA) pane of 20 stamps (Item 572500). The stamp will go on sale nationwide February 14, 2020, and must not be sold or canceled before the first-day-of-issue.

The Postal Service is pleased to issue Let’s Celebrate!, a new stamp that adds an extra dash of fun to celebratory greeting cards, invitations, and gift-bearing envelopes and packages. No matter the occasion — birthday, anniversary, holiday, engagement, new job, retirement — Let‘s Celebrate! will help send cheer to those deserving of well wishes. The stamp art features an array of colorful circles in varying sizes arranged in a random pattern. The letters in the word “celebrate,” cast in a dark green hue, appear inside several brightly colored circles on a white background. Art director Antonio Alcalá designed the stamp.

Item 572500, Let’s Celebrate! (Forever Priced at the First-Class Mail Rate) PSA Pane of 20 Stamps: Automatic Distribution

How to Order the First-Day-of-Issue Postmark:
Customers have 120 days to obtain the first-day-of-issue postmark by mail. They may purchase new stamps at their local Post Office or at The Postal Store website at usps.com/shop. They must affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:

FDOI – Let’s Celebrate! Stamp
USPS Stamp Fulfillment Services
8300 NE Underground Drive, Suite 300
Kansas City, MO 64144-9900

After applying the first-day-of-issue postmark, the Postal Service will return the envelopes through the mail. There is no charge for the postmark up to a quantity of 50. There is a 5-cent charge for each additional postmark over 50. All orders must be postmarked by June 14, 2020.

Technical Specifications:

Issue: Let’s Celebrate! Stamp
Item Number: 572500
Denomination & Type of Issue: First-Class Mail Forever
Format: Pane of 20 (1 design)
Series: N/A
Issue Date & City: February 14, 2020, Mesa, AZ 85201
Art Director: Antonio Alcalá, Alexandria, VA
Designer: Antonio Alcalá, Alexandria, VA
Typographer: Antonio Alcalá, Alexandria, VA
Modeler: Sandra Lane/Michelle Finn
Manufacturing Process: Foil Stamping, Offset, Flexographic, Microprint
Printer: Banknote Corporation of America
Press Type: Gallus RCS
Stamps per Pane: 20
Print Quantity: 300,000,000 stamps
Paper Type: Phosphor Tagged Paper, Block
Adhesive Type: Pressure-sensitive
Processed at: Banknote Corporation of America
Colors: Cyan, Magenta, Yellow, Black, Pantone Cool Gray 7
Other: Magenta Foil Luxor 28612, Teal Foil Luxor 361, Orange Foil Luxor 404
Stamp Orientation: Horizontal
Image Area (w x h): 1.42 x 0.84 in./ 36.068 x 21.336 mm
Overall Size (w x h): 1.56 x 0.98 in./39.624 x 24.892 mm
Full Pane Size (w x h): 6 x 7.24 in./152.4 x 183.896 mm
Plate Size: 160 stamps per revolution
Plate Numbers: “B” followed by five (5) single digits
Marginal Markings:
Front: Plate number in four corners
Back: ©2019 USPS • USPS logo • 2 barcodes (572500) • Plate position diagram (8) • Promotional text

Here are the first-day cancels for this issue: The Digital Color Postmark measures 2.67″ x 1.26″ The B&W pictorial measures 2.62″ x 1.23″