Let's take a step back and check on the key market drivers this week. The US-Iran conflict is still raging on and geopolitical tensions remain high. So, that is underpinning oil prices once again with WTI crude breaching $100 and Brent crude hitting $114 - its highest since May.Now, that sounds like a familiar backdrop for the bond market, doesn't it? Higher oil prices mean stronger inflation pressures, which should normally push up Treasury yields. Well, that has not been the case this week.Instead, Treasury yields have fallen sharply, with 10-year yields even slipping back below the 5% threshold in overnight trading and holding thereabouts since. But wait a second, shouldn't falling yields then buy some relief for stocks?You would certainly think so, especially when surging Treasury yields have been such a major bane for equities over the past two months. And yet stocks have been battered this week, with AI names in particular bearing the brunt of the pain. So, what gives?It's one thing to suggest that investors are perhaps starting to worry about growth conditions again. But considering how long that narrative has been brushed aside and the extent of the damage we are seeing in AI stocks, I think there is perhaps a rather different problem brewing beneath the surface.Let's jump straight into it and start with CoreWeave, shall we?That's not the most familiar name in the AI space. However, CoreWeave might well have been the stone that started an avalanche of worries about debt financing in the entire sector.Just take a look at the chart below, which shows how the cost of insuring against defaults among major AI-related companies has surged over the past year i.e. change in CDS spreads.The chart might seem complicated at first glance but the underlying message is quite straightforward. And that is investors are becoming more nervous about lending money to companies involved in the AI boom.CoreWeave stands out like a sore thumb, with its CDS spread widening by more than 500 basis points over the observed period. But what exactly does that mean?The simple way to think about it is to picture CDS as an insurance that investors can buy to protect themselves against a company failing to repay its debt. So, a five-year CDS provides that protection over five years and the spread simply reflects the cost of obtaining it. To give more context, 100 bps equals to 1% annually.As such, when CoreWeave's actual five-year CDS spread surged to above 1,000 bps last week, that implied roughly $100,000 annually to insure $1 million of debt. Now, that's an enormous premium to pay just to protect yourself against a potential default.And while CoreWeave is clearly the standout, the chart also shows that the worries aren't confined to just one company. Oracle's five-year CDS has climbed towards 300 bps, while Meta and Nvidia have seen theirs approach 100 bps.In the case of Oracle, it is being traded like junk credit due to aggressive debt-fueled infrastructure loans. Meanwhile, the five-year CDS level for Meta is near its historic peak so that helps to put things into better perspective. Having said that, I wouldn't put all these companies in the same risk category. Meta and Nvidia clearly have much stronger financial positions and liquidity than CoreWeave for example.However, it is clear that investors are beginning to question something bigger. And that brings us back to the same question we've been asking all year, that is who is going to pay for the enormous AI infrastructure boom, and how long before those investments generate sufficient returns?CoreWeave relies heavily on debt to finance data centres and computing infrastructure. Meanwhile, Oracle is also committing massive sums to AI expansion and Meta is also pouring billions into infrastructure. As for Nvidia, their fortunes are very much closely tied to that spending cycle.The major concern here is that if financing becomes more expensive or AI investment slows, the consequences could spread across companies that depend on one another for revenues, financing and growth.So, what does this have to do with the bond market and Treasury yields?Considering the backdrop above, investors are essentially growing more uncomfortable in wanting to hold riskier corporate debt and equities. So, what other options do they have left that pays a safe and good return in this market? Well, the answer is quite simply government bonds. And that pushes Treasury prices higher and yields lower as the demand flows in.But then, here's the catch though. Even if Treasury yields fall, corporate borrowing costs can still rise when investors demand a bigger premium for taking on credit risk. In other words, safer money is getting cheaper while riskier money is becoming more expensive.And that might explain why tech stocks aren't able to celebrate the sharp fall in Treasury yields. Investors may be worrying more about financing risks and future profits than the immediate benefit of cheaper government borrowing.With all that said, AI credit concerns aren't necessarily the only reason Treasuries are rallying. However, they are likely one part of the picture that could be helpful in explaining the market moves we're seeing this week.I mean, with inflation risks still lingering and oil prices elevated, falling Treasury yields aren't exactly hinting at better economic conditions. It could simply be investors starting to worry that something else might break first instead. This article was written by Justin Low at investinglive.com.