It'll keep accepting the registered warrants for another week, to July 24. This is the second IOU extension (most of the other big banks stopped accepting IOUs last week). From Citi's press release (h/t to Chris Sieroty):

"With the state so close to reaching an agreement, we believe the right course of action is to stand by our customers by providing them with all the resources they need to run their households and their businesses," said Citi California President Rebecca Macieira-Kaufmann in a press release. "We will continue to evaluate the budget situation and monitor our position daily as the negotiations progress."

From AP:

The move gives individuals and businesses receiving the IOUs more time to cash them as Gov. Arnold Schwarzenegger and lawmakers try to break an impasse on the state's $26.3 billion shortfall. California began printing IOUs earlier this month to conserve cash, sending them to thousands of state contractors and vendors.