Obamacare got some very good news on Thursday.

In 2009, the Congressional Budget Office predicted that a medium-level “silver” plan — which covers 70 percent of a beneficiary’s expected health costs — on the California health exchange would cost $5,200 annually. More recently, a report from the consulting firm Milliman predicted it would carry a $450 monthly premium. Yesterday, we got the real numbers. And they’re lower than anyone thought.

…The California exchange will have 13 insurance options, and the heavy competition appears to be driving down prices. The most affordable silver-level plan is charging $276-a-month. The second-most affordable plan is charging $294. And all this is before subsidies. Someone making twice the poverty line, say, will only pay $104-a-month.

Sparer plans are even cheaper. A young person buying the cheapest “bronze”-level plan will pay $172 — and that, again, is before any subsidies.

California is a particularly important test for Obamacare. It’s not just the largest state in the nation. It’s also one of the states most committed to implementing Obamacare effectively. Under Gov. Arnold Schwarzenegger — remember how that really happened? — California was the first state to begin building its insurance exchanges. The state’s outreach efforts are unparalleled. Its insurance regulators are working hard to bring in good plans and make sure they’re playing fair. If California can’t make the law work, perhaps no one can. But if California can make the law work, it shows that others can, too.

And perhaps others will. We’re beginning to see competition drive down proposed rates in some exchanges around the country. Remember Maryland, where CareFirst grabbed headlines with a shocking 25 percent proposed increase in rates? More plans have streamed in with lower bids. Kaiser Permanente, for instance, is only increasing its rates next year by 4.3 percent — a modest increase that will make CareFirst’s proposal almost impossible to sustain. My guess is when the exchange actually opens in October, CareFirst will have dropped its price substantially. If they don’t, then Kaiser and others will grab all the market share.