Nvidia's board approved a $150 billion buyback of its own stock, a move that rewards shareholders but adds to worries that the AI boom is being propped up by financial engineering.

• Nvidia is spending $150 billion buying back its own shares, the biggest such move any company has ever made.
• Much of that cash comes from circular deals with other AI firms, where companies swap stakes and projected revenue and both stocks jump without anything real changing hands.
• Nvidia paid roughly $19 billion in taxes last year while handing shareholders eight times that, after avoiding billions more through standard deductions and credits.
• Cities are still giving Nvidia incentives — Irving, Texas offered at least $23 million — even though it is the world's most valuable company.
• Jensen Huang insists AI safety failures are a solvable engineering problem, comparing the fix to how web browsers learned to contain risky code.

Outlook: Most observers agree this is a bubble, but nobody knows when it pops or what survives it.