Translating from one language/platform to another is something AI is very very good at, so this sounds like a good use of it, bonus points if they create a comprehensive test suite first.

Yes it will lead to new bugs, but the older code probably contains a ton of bugs already and is probably difficult to update (original writers long gone, docs out of date etc), so this is probably the best way out of that situation, as long as proper support is given afterwards so they don't end up in the same situation a year later (this is the hard bit).

The ra-ra commentary from the CEO is somewhat off-putting, but the idea is not all bad.

For me the next step is parallel businesses - that is capture the realm Im and out traffic of your company, probably easier for some than others, and then run different code bases against the same traffic, how much can be simplified, which code bases are easier to understand etc

I used claude to reverse engineer an old foxpro program. it setup a dos box and went through every screen. Looked at whatever files it could. Took a single week and it was 99% the same.

We have an embedded system in one of product offerings that was largely developed using a bunch of “antiquated” technologies (over the past twenty years) and over the past year the two software devs that maintained it have retired. This normally would have big problem, but the entire codebase was re-written, documented, and modernized in a matter of about 3 months (for about $20k in tokens, and a mid level developer spending 50% of their time on it over that period). So it doesn’t surprise me to think a company like Cisco has piles of situations like this.

AI rewrites of Cisco code? The infinite possibilities for endless backdoors is off the charts.

There also seems to be some weird hero-worship from the CEO, directed at this 27-YO engineer? Like, "he is the one who can save us."

Having to rewrite decades worth of legacy Cisco code is going to make Claude retire and start a goose farm.

As much as I dislike AI, having worked on Cisco gear for years, I can't imagine AI can put out a worse product. If the re-write is full of bugs and security holes and static SSH keys, then it has not changed at all.

Unless they also have 750K tests like sqlite do, I can't imagine this will go well, even if/especially if the legacy code warrants a refactor.

Does this one engineer have the domain knowledge to know WHY the old code was written the way it was, and what the graybeards would have done differently if they could start again now?

Otherwise he's just going to replicate all the legacy bugs and questionable design decisions.

Rewrite it in service of… what exactly?

If it isn't broken then break it!

I think Cisco is an interesting use case for AI, because it's code, probably:

-Works according to a defined specification

-Within the bounds of that specification, has a lot of code written to optimize speed, cost, latency, etc - all measureable goals

-Written in c, with all it's weakness

-Given limitless engineering work, some could be ported to better hardware

-the new system could be automatically compared to the old system for functional correctness

All those factors fit well with agent based development.

Btw, many of them are true in general to embedded systems.

There's no goal mentioned in this article as why 98% of the code needs rewriting.

Shocking to realize how many on HN do not realize that this is NOT a tall order, and has not been a feat for at least six months.

He'll pull it off, get feature complete, and spend a year or two with better models as they are released ironing it out. We just did an experiment, in four weeks generated 3500 commits, 200k sloc with a 1:1.15 ratio of production to test code and it all works very well. We are well on our way from 10x to 100x.

Well they say the last 20% of the work takes 80% of the time so if he gets the prototype in 4 weeks, which I have no doubt he will be able to do, and assuming that prototype is the first 80% of work, then he should be able to do this in 20 weeks. He even has some margin! Looking forward to seeing the results

Never thought I'd say this, but, "thank god I use unifi".

I doubt AI is gonna make or break this kind of project. It's the weird institutional knowledge that underpins a lot of these legacy code bases.

Anybody have an estimate of how much that is going to cost in token cost?

Most successful companies and innovative ideas come from middle aged founders and inventors. Silicon Valley loves the romantic notion of a contrarian young adult or even teenager "seeing what nobody else sees" , but they are the exception and not the rule.

Misleading title, someone should fix it. 98% of legacy code. Check out the full title of the article.

Don't they have no other AI news to share

I guess Cisco decided it has not alienated its customers enough till now & its finally time to get people running for the woods - at least if those peoples would like their network to continue working.

Anyone else thinking that tech and porn lingo is converging?

/r/whatcouldgowrong

Cisco that powers more than half of the backbone of all things online? Are we trying to lose control of AGI as soon as it emerges??

I mean, this is going to be easy. I've worked on Cisco gear before and this will be a simple job for AI. The big question is what the goal is... so you've rewritten new C++ code or ported to a newer version of Linux? Or you've unified the codebase of the Catalyst + Meraki switches?

Not clear to me what he's doing. Re-implement switching? Simplify features? Reduce LoC? Add test coverage? Either way, AI in that world will be helpful. I'm sure it'll spot all kinds of problems in opaque drivers that are hard to follow from MF specs.

ha ha .. that sounds like an Onion article. To be fair - if they did a narrow refactor to focus on fixing only obvious and known issues, they probably might be able to pull it off because a ton of that code is hairballs.

Is this like a PR piece for the guy? It's odd to see him singled out in a piece that would be normally be about the company, the CEO or the decision itself.

Claude make the Cisco ACI webui load in less than 10 minutes, make no mistakes

What's so special about the other 2%, is it good?

This decision is about so many things except the code that it deserves some kind of award.

Demonstrates fanatical devotion to capital’s golden idol - “yes, all of the code; yes, unlimited budget”. Doesn’t actually cost the company anything - only one engineer off task, any nuggets of value can be harvested as it progresses but any costs or big changes can be deferred until completion of the impossibly large open-ended mandate (ie never), one guy won’t have the personal bandwidth to spend so much that the “unlimited” part actually matters, and in case of emergency it only costs six months severance to make it all go away. It even rescues a fellow national from the ignominy of being employed so far below his previous station, there’s so much to like about it. Hmm? The code? What about it?

Literally anyone can do this

They need to cut cost & to figure out productivity per engineer. They're doing this b/c they are going to significantly cut their engineer workforce.

its never unlimited....

"According to a report by Fortune" - here's that report: https://fortune.com/2026/10/30/cisco-president-jeetu-patel-g...

Fortune's source was the CEO himself:

> “I’ve given him unlimited tokens because he’s going to refactor code,” Patel told Fortune at a small roundtable dinner. “So I’m like, you can go, you can go nuts.”

I think that Fortune story is better than the Tom's Hardware one. It ties the Cisco anecdote into a larger trend of some people deliberately hiring younger, less experienced developers for their AI projects - because they are more likely to be "AI native".

If i was an ex founder and having a low profile in a big company, I am doing it on purpose, either to have a peaceful life or heal from a burnout, definitely I don’t want to be on the spot like that, especially when I am not innovating anything new nor I will take any meaningful credit after since it will mostly go to AI, worse, if it didn’t work out I will have my career ruined being known to had an unlimited supply of tokens and still failed.

Source: https://fortune.com/2026/10/30/cisco-president-jeetu-patel-g... (https://news.ycombinator.com/item?id=50303001)

Maybe Stanford found some more of their stolen code being used by Cisco. /s Cisco origins is a fascinating subject.

"At most companies, only someone with decades of experience under their belt would be trusted with a project this size. Patel thinks that’s a problem.

“If you don’t hire the early-in-career [workers], and you just let your workforce continue the way that they were, where do fresh ideas get injected? How do you challenge the status quo?” he said."

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This would be an interesting approach for a bleeding edge startup that's betting big on producing something novel or going bankrupt. If you're going to bet the company on one guy and some AI, that's bold. He'd better have some serious chops and not be merely a slick salesman.

However, Cisco is an infrastructure company. Status quo is what most people want from an infrastructure company. You don't want your Cisco stuff to suddenly start doing new, innovative things that require a complete redux of everything built on top of it. This, of course, assumes that having one guy do a refactor of your entire code-base produces something "innovative" rather than a cavalcade of snafu's.

It's probably not the best time to be holding CSCO.

So there's a real risk that Cisco might become history in just a few years. Taking that kind of risk with a rather unproven technology has to be psychosis. Or is that kind of belief a form of Religion?

rewriting code is the easy part

it's the testing in real world usage to shake out all the edge cases and bugs that's hard and that you can't just write unit tests for

First LLM PTSD case coming soon. You heard it here first, folks.

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I suspect we are approaching a world where this makes sense to do annually. Opus 5.5 is good enough to improve on most codebases, and Opus 7 will no doubt be good enough to improve on that.

'98% of the company's legacy code' is very vague. How many code bases? How each code base is connected to any supported Cisco product? How many KLOC the company's legacy code?

What a mess of an article. Hard to read. Chasing the jabs and the stabs for clicks.

A lot of the commenters here are still living in early 2026. Late 2026 AI can absolutely demolish this kind of job. It can clone photoshop! You think this is going to be harder than that?