Something being simultaneously described as a "30 sheet, mind-numbingly complex Excel model" and "testable" seems somewhat unlikely, even before we get into whether Claude will be able to test such a thing before it runs into context length issues. I've seen Claude hallucinate running test suites before.

▲

martinald 7 hours ago | parent [-]

It compacted at least twice but continued with no real issues.

Anyway, please try it if you find it unbelievable. I didn't expect it to work FWIW like it did. Opus 4.5 is pretty amazing at long running tasks like this.

▲

moregrist 7 hours ago | parent | next [-]

I think the skepticism here is that without tests or a _lot_ of manual QA how would you know that it did it correctly?

Maybe you did one or the other , but “nearly one-shotted” doesn’t tend to mean that.

Claude Code more than occasionally likes to make weird assumptions, and it’s well known that it hallucinates quite a bit more near the context length, and that compaction only partially helps this issue.

▲

skybrian 3 hours ago | parent [-]

If you’re porting some formulas from one language to another, “correct” can be defined as “gets the same answers as before.” Assuming you can run both easily, this is easy to write a property test for.

Sure, maybe that’s just building something that’s bug-for-bug compatible, but it’s something Claude can work with.

	▲	gregoryl an hour ago \| parent [-]
		For starters, Python uses IEEE 754, and Excel uses IEEE 754 (with caveats). I wonder if that's being emulated.

▲

stavros 7 hours ago | parent | prev [-]

I generally agree with you, but I tried to get it to modernize a fairly old SaaS codebase, and it couldn't. It had all the code right there, all it had to do was change a few lines, upgrade a few libraries, etc, but it kept getting lots of things wrong. The HTML was wrong, the CSS was completely missing, basic views wouldn't work, things like that.

I have no idea why it had so much trouble with this generally easy task. Bizarre.