Putting Three AIs to the Test: ISO/AMT Tax Scenarios

Exercising Incentive Stock Options (ISOs) can get complicated fast, especially when it comes to the Alternative Minimum Tax (AMT). Curious to see how different AI assistants would handle this, I asked three of them—ChatGPT 5 Pro, Claude, and Manus—the same question: What’s the AMT impact if I exercise and sell ISOs?

Here’s how they stacked up.

Here’s how they stacked up.

🏆 ChatGPT 5 Pro: Clear Winner

ChatGPT broke the problem down in a way that made sense. It separated Federal vs. State impacts, provided detailed calculations, and even offered minimum and maximum ranges. Most importantly, it sounded confident and logical—exactly what you want when dealing with numbers that can have big consequences.

🤔 Claude: Too Generic

Claude’s answer felt a little surface-level. It gave a generic calculation but didn’t probe for key missing details (like Fair Market Value). The tone leaned cautious, with repeated reminders to consult a tax professional. While that’s fair advice, the lack of depth left me wanting more.

🕒 Manus: Methodical but Confused

Manus took its signature structured approach, first outlining the steps it would take:

1. Research AMT rules and thresholds

2. Calculate implications

3. Provide analysis and recommendations

   
   

It also showed the sites it was crawling in real time, which was interesting to watch while you wait. It definitely took much longer time for it to provide me the initial response. But the follow-up questions (about FMV and vesting/exercise dates) muddied things. It seemed to mix up exercising, selling, and vesting—three scenarios with very different tax outcomes. In the end, like Claude, it pointed me back to a tax professional.

Final Takeaway

I wouldn’t rely on any AI alone for major ISO decisions (too much money at stake). But in this test, ChatGPT 5 Pro was the clear standout—it gave me the most structured, confident, and useful analysis of the three.