AI companies don't buy government bonds, but some AI companies sell their own bonds. Google and Oracle for example and I believe SoftFail is also looking to sell bonds so they can refinance a loan they used to get a stake in ClosedAI.

Google's most egregious bond is one that matures in 2126. You'll only be paid interest until a century from now when you'll get the principal back. A ridiculous investment if you ask me, but they say it's fine because thanks to AI they'll earn a gazillion dollars by then and surely won't go bankrupt.

It should also be mentioned that a large proportion of bonds aren't government bonds at all, companies selling bonds isn't anything new, there's basically two ways for a company to raise funds: Sell bonds or sell equity. Bonds are preferable if you know you can pay them back easily because nobody gives up any shares.