The German manufacturer, which is set to supply the project with its 3.6MW turbines, told Bloomberg News that the construction of components has begun in time for the ITC and PTC deadline at the end of the year.
There have been serious questions over whether the 468MW project off the coast of Massachusetts would meet the criteria for the subsidy, therefore threatening its viability.
Siemens wind CEO Markus Tacke told Bloomberg that work on the foundations for the project's turbines has begun, saying that he is convinced it would qualify for the tax credit.
The ITC, which along with the production tax credit (PTC) expires on 1 January, reimburses developers as much as 30% of the initial capital costs and could mean $780 million for Cape Wind.
Even more hangs on the qualification, with Danish pension fund PensionDanmark warning that a $200 million loan it has offered Cape Wind is dependent on the project obtaining tax credit support.
Cape Wind signed a $15 million pre-cabling works contract in July but has not made any statements regarding solid progress on the project since.
To qualify for both tax credits, construction must have started at projects by 31 December. Developers can show this by starting "physical work of a significant nature" at the site or at a factory that is making equipment for the project.
Another option is to demonstrate that the developer has incurred at least 5% of the total project cost.
The project has state and federal permits and National Grid and utility Nstar have agreed to buy the power under a power purchase agreement.