The vast majority of that money will go to hire more staff to pursue multi-millionaire tax dodgers, not to modernise the tech, so the previous comment was pretty misleading.
The tech modernisation is supposed to cost about $2.5 billion over a decade or so. Just for rough numbers that's about what 1,000 developers would cost. That sounds like a lot but the IRS claims they need to rewrite 600 different applications, most of which are at least 20 years old. And the Individual Master File (IMF) is 60 years old.
No idea what the systems are and I doubt each one of those 600 will take the full 5+ years. But you could see how they could pretty quickly get to needing hundreds and hundreds of developers for years at a stretch.
Looking over their tech modernisation plan ("Objective 4") in Publication 3744 they have a lot of work so the number is high but not like insanely impossibly high.
The original comment was confusing - they're getting $60B, and also have a mandate to modernize. Only a minority of that money is actually being spent on the modernization. Most of it is being spent on additional auditing of tax returns - it's well known that every $1 spent on audits brings in more than $1 of additional revenue, and we're nowhere near the breakeven point. It's expected that the additional auditing will pay for itself several times over - even if you count the modernization spend against it as well, the government will see a large ROI on this $60B (they're expecting additional revenue of over $200B from the extra auditing).
