CS PhD stipends are high because they have to be. Industry is right there, waving salaries that make any stipend look like a rounding error, and departments know it. That pressure is the whole story of CS funding, and honestly it is your leverage.
The top-paying CS programs cluster at well-funded privates and a few aggressive publics, the ones competing hardest for the same small pool of strong applicants. They are not bidding against each other so much as bidding against your job offer. Keep that in your head during every conversation with a department, because it changes the dynamic.
Which brings up negotiation. PhD offer negotiation is more normal in CS than in most fields, and departments expect strong candidates to have options. You do not need a PhD offer negotiation coaching app to do this well. You need what a coach would give you: real numbers. Walk in knowing what peer programs pay and what the local cost of living does to those numbers, and the conversation changes. Polite, specific, and backed by data beats hopeful every time.
But the same old rule applies before you compare anything. Adjust for cost of living first. CS programs concentrate in expensive tech hubs, which eats into the premium fast. The nominal gap between the highest and lowest CS stipends shrinks a lot once you subtract rent. I have seen offers that looked twenty percent apart turn into near-identical take-home after housing.
CS funding has its own quirks too. Many CS PhDs are funded as research assistants on faculty grants, which is great until a grant cycle goes badly. Programs with fellowship first years or guaranteed departmental funding give you a buffer. Ask how the money flows, not just how much there is. The flow is the part that breaks.
And have the opportunity cost conversation, the one nobody wants to have. Five years of stipend instead of five years of industry salary is an enormous gap. Worth it, for a lot of people, but only with full information. Compare the stipends, the cities, and the funding guarantees across programs at phdstipend.fyi before you decide anything.