Microsoft has previously stated that Windows 10 will launch sometime this summer, but AMD's president and CEO has narrowed this down to "the end of July."
Speaking during an investor call, AMD's Lisa Su let a date slip:
"What we also are factoring in is, you know, with the Windows 10 launch at the end of July, we are watching sort of the impact of that on the back-to-school season, and expect that it might have a bit of a delay to the normal back-to-school season inventory build-up."
While this date could very well be a case of misspeak, AMD is a significant cog in the PC machine, and would be privy to insider information about Microsoft's future plans.
That said, unless that date comes from Microsoft, it's still unofficial.