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

The Postal Service celebrates hip hop with four new stamps in a pane of 20. Since its inception more than four decades ago, the electrifying music, dance and art movement has profoundly influenced American and global popular culture. The stamp art features photographs taken by Cade Martin that depict four elements of hip hop: MCing (rapping), b-boying (breakdancing), DJing and graffiti art. The bold, digitally tinted images are intended to appear in motion. The words “Forever” and “USA,” “Hip Hop,” and the name of the element featured appear across the top of each stamp. Art director Antonio Alcalá designed the stamps, which are highlighted with a vivid yellow, green, red and black color scheme. The title of the stamps, printed in red and black, is centered on the top of the pane.

These stamps will be issued Wednesday, July 1, in New York, NY (a change from the date given in the USA Philatelic catalogue).

Here are the Scott catalogue numbers for this issue:

5480 (55¢) Hip Hop – MC with microphone rapping
5481 (55¢) Hip Hop – B-boy dancing
5482 (55¢) Hip Hop – Graffiti art
5483 (55¢) Hip Hop – DJ at turntable
a. Block or vert. strip of 4, #5480-5483

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

Updated May 28th:

The USPS says there will be no first-day ceremony for this isue, but it will till go on sale on July 1^st.

From the Postal Bulletin:

On July 1, 2020, in New York, NY, the United States Postal Service® will issue the Hip Hop stamps (Forever® priced at the First-Class Mail® rate) in four designs, in a pressure-sensitive adhesive (PSA) pane of 20 stamps (Item 476500). The stamps will go on sale nationwide July 1, 2020, and must not be sold or canceled before the first-day-of-issue. The Hip Hop pane of 20 stamps may not be split, and the stamps may not be sold individually.

The Postal Service™ celebrates hip hop with four new stamps in a pane of 20. Since its inception more than four decades ago, the electrifying music, dance, and art movement has profoundly influenced American and global popular culture. The stamp art features photographs taken by Cade Martin that depict four elements of hip hop:

• MC-ing (rapping),
• B-boying (break dancing),
• DJ-ing, and
• Graffiti art.

The bold, digitally-tinted images are intended to appear in motion. The words “Forever” and “USA,” “Hip Hop,” and the name of the element featured appear across the top of each stamp. Art director Antonio Alcalá designed the stamps, which are highlighted with a vivid yellow, green, red, and black color scheme. The title of the stamp issuance, printed in red and black, is centered on the top of the pane.

No automatic distribution to post offices.

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 – Hip Hop 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 November 1, 2020.

Technical Specifications:

Issue: Hip Hop Stamps
Item Number: 476500
Denomination & Type of Issue: First-Class Mail Forever
Format: Pane of 20 (4 designs)
Series: N/A
Issue Date & City: July 1, 2020, New York, NY 10199
Art Director: Antonio Alcalá, Alexandria, VA
Designer: Antonio Alcalá, Alexandria, VA
Typographer: Antonio Alcalá, Alexandria, VA
Photographer: Cade Martin, Bethesda, MD
Modeler: Joseph Sheeran
Manufacturing Process: Offset
Printer: Ashton Potter (USA) Ltd. (APU)
Press Type: Muller A76
Stamps per Pane: 20
Print Quantity: 20,000,000 stamps
Paper Type: Nonphosphored Type III, Block Tag
Adhesive Type: Pressure-sensitive
Processed at: Ashton Potter (USA) Ltd. (APU)
Stamp Orientation: Vertical
Image Area (w x h): 0.84 x 1.42 in./21.336 x 36.068 mm
Stamp Size (w x h): 0.98 x 1.56 in./24.892 x 39.624 mm
Full Pane Size (w x h): 5.92 x 7.45 in./150.368 x 189.23 mm
Press Sheet Size (w x h): 11.84 x 22.35 in./ 300.736 x 567.69 mm
Colors: PMS 7549 C Yellow, PMS Black 6 C, Cyan, Magenta, Yellow
Plate Size: 240 stamps per revolution
Plate Number: “P” followed by five (5) single digits
Marginal Markings:
Front: Header: Hip Hop • Plate number in bottom two corners
Back: • ©2019 USPS • USPS logo • Two barcodes (476500) • Promotional text • Plate position diagram (6)

Here are the first-day postmarks for this issue: The Digital Color Postmark for this issue measures 2.60″ x 1.31″ The pictorial postmark measures 2.70″ x 1.20″