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

In 2020, the Postal Service issues four new stamps in a booklet of 20 available for notes, cards and letters of thanks sent to acknowledge a favor, an act of kindness, a job well done or gifts sent for any occasion. Highlighted in gold foil are the words “Thank you” in cursive script and an elegant floral design that swirls through and around the words. Each stamp features one of four background colors: blue gray, deep blue, muted green or soft maroon. Greg Breeding was the art director. Dana Tanamachi was the stamp designer and lettering artist.

These stamps will be issued Friday August 21 at Hartford, CT, planned site of Great American Stamp Show (American Philatelic Society / American Topical Association / American First Day Cover Society).

The Scott catalogue numbers for this issue are:

5519 Rose brown background
5520 Olive background
5521 Slate blue background
5522 Violet background
a. Block or 4, #5519-5522

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

Although the postmark will still say “Hartford, CT,” the issue will have a virtual first-day ceremony as part of Virtual Stamp Show, the joint venture of the American Philatelic Society, American First Day Cover Society and the American Topical Association. The latter will be the host. It will be held at 2 p.m. and is free, but to attend, you must register for the show.

Updated August 13th:
[press release]
U.S. Postal Service Premieres Two New Stamp Issuances
Stamp Show to Host Dedication Ceremonies for Innovation and Thank You Forever Stamps

WHAT: The U.S. Postal Service will dedicate stamps in two new sets, one celebrating the American spirit of innovation and the second offering expressions of thanks.

News of these Forever stamps is being shared with the hashtags #InnovationStamps and #ThankYouStamps.

WHERE:
Separate events for these designs will be held during the American Philatelic Society Virtual Stamp Show and will be posted on the Postal Service’s Facebook and Twitter pages. Please visit usps.com/innovations and usps.com/thankyou for details of the virtual stamp dedication ceremonies.

WHEN:
Thursday, Aug. 20, 2020, at 2 p.m. EDT
Innovation Forever Stamps
Dedicating official: Acting Chief Customer and Marketing Officer Steven Monteith

Friday, Aug. 21, 2020, at 2 p.m. EDT
Thank You Forever Stamps
Dedicating official: Chief Commerce and Business Solutions Officer Jacqueline Krage Strako

BACKGROUND:
Innovation stamps feature five new stamp designs in a pane of 20, showcasing fields in which U.S. scientists and engineers have made significant contributions that have touched lives around the world.

Each stamp design features a photograph of a subject representing Computing, Biomedicine, Genome Sequencing, Robotics and Solar Technology. The word INNOVATION overlays each image in a holographic foil.

Thank You stamps will add visual appeal to notes, cards and letters of thanks to acknowledge a favor, an act of kindness, a job well done or gifts received for any occasion.

The words “Thank You” are highlighted in gold foil in cursive script. An elegant floral design swirls through and around the words. Each of the four stamps features a background color of soft maroon, muted green, grayish blue and purple.

Pre-orders of Innovation and Thank You Forever Stamps can be made online at usps.com and by phone at 800-STAMP24 (800-782-6724).

Updated August 4th:
Here are the first-day cancels for this issue:The Digital Color Postmark for this issue measures 2.89″ x 1.39″ The Pictorial Postmark for this issue measures 2.74″ x 1.46″

Updated July 31st from the Postal Bulletin:

On August 21, 2020, in Hartford, CT, the United States Postal Service® will issue the Thank You stamps (Forever® priced at the First-Class Mail® rate) in four designs, in a pressure-sensitive adhesive pane of 20 stamps (Item 572900). The stamps will go on sale nationwide August 21, 2020, and must not be sold or canceled before the first-day-of-issue. The Thank You pane of 20 stamps may not be split and the stamps may not be sold individually.

In 2020, the United States Postal Service issues four new stamps in a pane of 20 available for notes, cards, and letters expressing thanks, and sent to acknowledge a favor, an act of kindness, a job well done, or gifts for any occasion. Highlighted in gold foil are the words “Thank you” in cursive script and an elegant floral design that swirls through and around the words. Each of the four stamps features one of four background colors: blue gray, purple, muted green, and soft maroon. Greg Breeding was the art director. Dana Tanamachi was the stamp designer and lettering artist.

Item 572900, Thank You (Forever Priced at the First-Class Mail Rate) Pane of 20 Stamps will not have 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 – Thank You Stamps
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 December 21, 2020.

Technical Specifications:

Issue: Thank You Stamps
Item Number: 572900
Denomination & Type of Issue: First-Class Mail Forever
Format: Pane of 20 (4 designs)
Series: N/A
Issue Date & City: August 21, 2020, Hartford, CT 06101
Art Director: Greg Breeding, Charlottesville, VA
Designer: Dana Tanamachi, Seattle, WA
Typographer: Dana Tanamachi, Seattle, WA
Modeler: Sandra Lane/Michelle Finn
Manufacturing Process: Foil Stamping, Flexographic
Printer: Banknote Corporation of America
Press Type: Gallus RCS
Stamps per Pane: 20
Print Quantity: 200,000,000 stamps
Paper Type: Phosphor, Block Tag
Adhesive Type: Pressure-sensitive
Processed at: Banknote Corporation of America
Colors: Black, Red PMS 4985, Teal PMS 4185, Green PMS 5773, Blue PMS 7545
Other: Gold Foil
Stamp Orientation: Vertical
Image Area (w x h): 0.77 x 1.050 in./ 19.558 x 26.67 mm
Overall Size (w x h): 0.91 x 1.19 in./23.114 x 30.226 mm
Full Pane Size (w x h): 5.55 x 5.76 in./140.97 x 146.304 mm
Press Sheets Size (w x h): 11.1 x 23.04 in./281.94 x 585.216 mm
Plate Size: 160 stamps per revolution
Plate Numbers: “B” followed by five (5) single digits in four corners
Marginal Markings:
Front: Plate number in four corners
Back: ©2019 USPS • USPS logo • 2 barcodes (572900) • Plate position diagram (8) • Promotional text