This contest celebrates the society’s 25th anniversary. Their website says, “What Is Tanka Prose? If you know haibun, where prose is sprinkled with or followed by haiku, tanka prose is essentially the same except that it uses tanka instead of haiku. … Submit one tanka prose piece per contest entrant. A title and one to three tanka should be included with prose. The prose portion should not exceed 300 words.”
Value: $100, $50, $25
Deadline: 31 July 2025
Open for: All writers
Details here and here. (They also run the annual Sanford Goldstein International Tanka Contest, the deadline for which has passed.)

Deadline: July 31st, 2025