"The September 2013 Standard arena rotation is now online. On the first Monday of each month, we will be cycling the Standard arena pool. Rather than only having access to the same standard arenas day in and day out, each month we will now feature 25 arenas selected as playable for Standard-level matches.
Newly released arenas will remain exclusive for at least three months, but every other arena is eligible to be included in the cycle."
Standard Map Pool:
Start date: September 2, 2013
End date: October 7, 2013
Asylum
Arcane Citadel
Battleforged
Blood Run
Cold War
Concrete Palace
Courtyard (CTF)
Dreadful Place
Eye to Eye
Fatal Instinct
Gothic Rage
Hidden Fortress
Industrial Accident (CTF)
Ironworks (CTF)
Japanese Castles (CTF)
Lost World
Overlord (CTF)
Reflux (CTF)
Retribution
Scornforge (CTF)
Space CTF (CTF)
Theatre of Pain
The Edge
Trinity
Hell's Gate
links: Official Announcement