Unfortunately limited to $10k per year, but at that rate everyone should be buying up to the limit.

Limited to 10k/year

$15k; you can buy $5k with your tax return. $30k if you've a spouse.

Ha ha, what tax return? Thanks, though. Setting up an account today.

If you want, you can overpay taxes by $5k to get a refund to put into I Bonds.