The million dollar (perhaps literally) question is – could @kentonv have written this library quicker by himself without any AI help?
I estimate it would have taken a few weeks, maybe months to write by hand.
That said, this is a pretty ideal use case: implementing a well-known standard on a well-known platform with a clear API spec.
In my attempts to make changes to the Workers Runtime itself using AI, I've generally not felt like it saved much time. Though, people who don't know the codebase as well as I do have reported it helped them a lot.
I have found AI incredibly useful when I jump into other people's complex codebases, that I'm not familiar with. I now feel like I'm comfortable doing that, since AI can help me find my way around very quickly, whereas previously I generally shied away from jumping in and would instead try to get someone on the team to make whatever change I needed.
Maybe because (and I'm quoting that article) it is still lacking in what it should have that you managed to accomplish this task in "few days" instead of "a few weeks, maybe months".
Maybe the bottleneck was not your typing speed, but the [specific knowledge] to build that system. Because if you know something well enough, you can build it way faster, like rebuilding something from scratch, you will be faster as you already know the paths. In which case, my question would be: would not be writing this as fast, or maybe at least more secure and reasonable, if you had the complete knowledge of the system first.
Because contrary to LLMs, humans can actually improve and learn when they do things, and they don't whey they don't do things. Not knowing the code to the full extent is worth the time "gained" by using the LLM to write it?
I think it's very hard to estimate those other aspects of the thing.