Excellent,
Didn't see 'when' (Date) that free upgrade might be offered
You will have one year from the official release date of Windows 10 to convert your Windows 8 and Windows 7 free of charge.
The conversion or upgrade will first be made available for the Windows 8 platform and then followed for those using Windows 7.
Hope that helps answer your question.
( It was a very interesting webcast this morning and can now be seen recorded at the same link I had posted)