For some background on me to set the context for the following opinion:

- been a SRE/DevOps at banks/hedge funds for almost 20 years

- now work in L1 crypto

- have been coding since I was 12 and have also been using frontier models for the past year (including running multiple agents at the same time etc).

My thoughts:

The models are indeed amazing. They can read large codebases, find bugs, infer the root cause of an issue from partial logs etc etc.

They do still hallucinate. WAY less than they used to but it's still non-zero. In a way that's worse b/c the model will spit out a complex piece of software and say "Yep, no mistakes. I even wrote tests and they all pass!" You might think "Phew, that's great!" but in the same way we've all found bugs in production code written by smart people, there will be bugs here too.

I say this not to imply that you have to read all of the code. I say if only to underline that for big complex systems, the "let's write unit tests for the parts that ABSOLUTELY HAVE TO BE CORRECT" is still just as important as it ever was. I'm thinking of examples like:

- the order and execution handler of a trading system

- avionics flight controls

- healthcare related medical devices

- etc

As an example: I was working on a complex system. I wasn't sure if the LLM code was actually correct so I wrote up a quick script that I checked, line by line, to be 100% sure it was working as I expected. I then used that script to double check the LLM. I didn't read all of the code the LLM created. The sense of "ok, now this works" was astounding.

I'll add, a lot of the developers I work with are going this "hybrid" route too where they will have the LLM write code and tests but then go back in and double check.

In closing, a lot of these big rewrites with LLMs are possible only b/c the devs KNOW, FOR A FACT, that the unit/integration tests are correct. I'm still not convinced that you can have LLMs write all of the code and all of the unit tests and be 100% sure that it's all correct. (I will admit that this has always been difficult and even the pre-LLM days were not a guarantee that all of the code wa s correct)

You can have almost 100% tests coverage and green tests and still have a plane crash and LLMs shilling with you that everything is ok. To me it seems we havent learned yet tests coverage means nothing without solid code