Cisco gives engineer unlimited AI tokens to rewrite legacy code | Hacker News Reader

Cisco gives engineer unlimited AI tokens to rewrite legacy code

fortune.com

316 pointstaubek393 comments

We just recently use Claude Code to port an old Coldfusion site to Java Spring and it went amazingly well. It's around 50K lines of Java, one of our engineers did it in his spare time over about a week, using the $200/mo Claude plan. We had been talking about doing it for at least the last dozen years but never found the time. It would have taken around 12-18 engineer-months to do this manually.

He had the translation use browser integration to compare the new site to the old site automatically. The result was so good that he had to change background color on the new site because he couldn't be sure that he was testing the new site; it was so close to the original he was paranoid about accidentally being on the old site and not knowing it. The whole thing was done in under 2 weeks, including coding, developer testing, tester testing, and deployment. It's been in production 4-6 weeks now and we've had no reports of problems.

Okay so assuming engineer compensation of $200k, you’re suggesting something like a thousand-fold productivity increase on this task in terms of cost and 26x or more in terms of time?

There’s no real productivity increase because that project was not worth pursuing before AI. It’s like wanting to build a tunnel in the 1700s by having 200 people digging it by hand, vs actually building it using machines in the 2000s. We don’t say there was an increase in productivity. The technology enabled a project that used to be a dream.

What is the unit for productivity here, though? Time required to complete this one task, which was never attempted before and never will be again? That's fine, but economically uninteresting.

Ultimately, the economic analysis needs to use monetary units. How much faster can return on investment be realized, and at what scale? This analysis has proven elusive because people believe that the very definition, not just the execution, of a task can be delegated to an LLM (which in some trivial sense must be true because means and ends are never sharply distinguished).

“On this task” is the really important qualifier. The requirements were already in place, and this was something that wasn’t a business priority for a decade.

> thousand-fold productivity increase

The engineer still spent a week there.

Productivity went down because an engineer spent 2 weeks doing what nobody would have previously done /s.

On a more serious note, the productivity increase is the time which will no longer be needed to maintain two production systems instead of one.

Holy moly, those numbers can only mean... the AI market must be worth at least one thousand quintillion billion dollars!

How are you using the monthly subscription plans for commercial work (unless you're just ignoring the actual terms and conditions)?

I've seen reports that say any organisation over 150 people needs to be paying API billing with Anthropic but here in the UK the terms seemed to be very clear when we looked that any sort of professional/commercial use is not permitted on the monthly plans like Pro and Max and you need something like API tokens or maybe some enterprise plan on their commercial terms for that kind work.

There are subscription plans for business, at least where I am.

https://support.claude.com/en/articles/9266767-what-is-the-t...

My understanding is that it's only available under 150 employees.

Does it change it that we are an organization of 8 people? As far as I know our use is permitted, but LMK if that isn't the case.

> He had the translation use browser integration to compare the new site to the old site automatically.

I imagine this is a luxury cisco will not have for validation

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.

Cisco over the last years, has been nothing but a flurry of security issues, hundreds ( thousands? ) of CVEs and usually are well known to ship their devices with hardcoded passwords and hidden accounts.

It got so bad, that in their last global event in Amsterdam in the keynote ( available on YouTube ) their CEO (or CTO.. cant recall) started within the first minutes by apologizing for the past security issues.

Nothing on this is likely to stop this trend.

To be fair Claude has educated me on numerous vulnerabilities in my legacy code. I imagine I’m not the only one.

Sounds like Claude will do a better job of it then.

I had Abliterated GLM pull one of the Core router firmwares and spent about $150 reverse engineering the BGP parsing code. It was pretty horrifying seeing all of that C/C++ emerge from Ghidra. However, it found nothing exploitable at all: the code seems to have been through so much trial by fire (including CVEs within the last few years) that they just poured engineering discipline into making it safe, at least at the level of memory management. But the cost of maintaining code like that must be enormous, and I doubt it scales to all of their other products and interfaces. I’m very much on team rewrite.

Note of course, that the code that comes out of Ghidra is significantly worse than the source code. Aside from the obvious like variable names, more complicated language features, like templates or macros, won't roundtrip.

(Unless I'm misunderstanding your comment, and "horrifying" was not meant to describe the code itself.)

Did you run abliterated GLM locally?

As good as it is, we saw a lot of problems with these translations as the code was rewritten without understanding. I remember a security issue where a runtime went from single threaded to multithreaded for example.

Testing is still the long pull, even if you have an engineer with good expertise.

Yes sure, it's not a panacea, but this is a use-case for which AI is quite suited. I'm not a huge fan of using to write without human intervention, so personally I'd want a lot of human involvement...

"as the code was rewritten without understanding."

good thing they have unlimited token, now they would have 5 different model reviewing the work

Problem with legacy code is that with time some of the bugs have become features without users even knowing it or remembering it.

Yeah you can not deploy this to customers with the hardware already in production if it mass fixes bugs and improves behavior because those are likely breaking changes.

They have to modernize the code while keeping all weird edge case behaviour. I think this can be done. And I suspect that is probably the request.

The issue is deciding what is weird edge case behavior and what are bugs. It can be a fine line.

https://lawsofsoftwareengineering.com/laws/hyrums-law/

Every bug is someone else's workflow: https://xkcd.com/1172/

Also, extensive commenting inside codebases is useful documentation, incl. these kinds of incidents. Good code documents the how, but not why. Comments shall also include the "why" where applicable.

> and is probably difficult to update (original writers long gone)

The new program won't be any easier on that front. It literally doesn't have an original writer. So the new program will certainly be maintained and updated by a LLM, at which point I wonder if the language switch mattered at all?

> the older code probably contains a ton of bugs already

The billion-dollar question is: what things might an LLM see as a bug or candidate for simplification, but supported a unique use case? https://xkcd.com/1172/ as always is prescient.

The thing about "rewrite X in two weeks" - or an entire company's worth of code in 24 months - is that it gives scarcely little time to do incremental rollouts to limit splash radius, or to identify and gather stakeholders to whom one can ask "why was this necessary" (or who can be guided to mine their emails and chat logs for conversations about the same).

Which is not to say this shouldn't be done! Let AI-native people guide the momentum with all the fervency of a hungry founder... but find project leaders who are committed to the empathy towards those who depend on the quirks of their workflows - ones who will create "curiosity loops" that try to bring in stakeholders as rapidly as possible on material questions, not just "continue, follow what you think is best" loops when the LLM brings up an open business question.

> bonus points if they create a comprehensive test suite first.

If they didn't have a very comprehensive test suite at the end of the exercise, then based on my experience someone is kidding themselves.

A friend had a tiny accounting system - maybe 15k loc, written in a combination of Python 2.7 / bash / LaTeX. I migrated it to Python 3.13 or whatever by hand. I did try using an LLM for that, but it did things like delete chunks of functionality so I had to check every bloody line it changed. Translating Python 2 to 3 is a fairly mechanical process, so traditional tooling worked better. Then I thought I'd explore LLMs by getting one to translate it to Rust.

The original had no tests or doco. As others have noted, the first attempt superficially looked identical to the original near immediately. You think "Wow". But in my case, it was riddled with bugs. When I asked it to fix bugs I noticed, it introduced as many bugs as it fixed.

I eventually figured out the limited context meant it kept forgetting all the lessons it learned when it fixed things, so it reintroduced old bugs and misunderstandings fixed earlier. (Like I said, this was a learning exercise.) Which is how I came to the same realisation a lot of the industry has - the solution to the context problem is you have to define the application via tests, then tell it to make the tests pass.

The tests rapidly became huge and unwieldy, so part of the exercise became DRY'ing the test code out by getting the LLM to build an integration test harness. The harness captured UI responses, files written, emails and printer output; froze time; fed in known input; and compared the outputs with results captured from the original program.

That cured the bug injection problem, but there were still bugs in all sorts of unexpected places. By unexpected I mean places I would be surprised to find them in human-written code. Human devs run the program in the same way human users do. They use the backspace key and the browser back button to navigate as they test their work. AIs don't. They will use APIs to inject test data unless you explicitly tell them to do it differently. The size of the tests exploded to be far, far larger than the code. Rather than coding I spent my time testing, telling the LLM to write tests to catch the errors I found, then writing standing prompts to try and prevent similar errors. It was meant to be a vibe-coded project, but in the end I got worried about code paths I suspected existed, so I looked at the code anyway to see if they were written the wrong way. Sometimes they would have blown up, say when the SMTP server was offline. To be fair, there was no need to look - I could have just asked the LLM. How a programmer without decades of experience would know what to ask is a mystery.

There is no doubt I got a working Rust program faster than if I had written it myself. Several times faster - but not orders of magnitude. If it was a program I had written, so I was very familiar with it, and it had excellent doco, and a high-coverage test suite, it probably would have been orders of magnitude faster. I think Bun's Rust migration might be an example of that - it's a best-case scenario. There were lots of early announcements, but it took over 6 weeks before they were confident enough to ship it in Claude Code.

But an "I migrated a program with hundreds of thousands of lines of code to a new language and ended up with production-ready code in a few days" - sorry, pics or it didn't happen.

'Superficially identical, riddled with bugs' is the scariest version of this. When it kept reintroducing old bugs, did writing those bugs down as tests first help, or did it just break the tests too?

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.

That's really interesting.

What have been achieved using this port?

And how did you make sure the port is correct?

> And how did you make sure the port is correct?

I'd ask "did you make sure the port is correct?"

Curious, why did it take 3 months and not a few days? Honest question, just curious about what is consuming all the time in a project like this?

I didn’t work on it, but from afar it was a mission critical in-production system (with multiple modules / services like data collection, interpretation, visualization, etc) with minimal documentation and numerous other software dependencies. A lot of the work was understanding exactly how it worked and what/how it interacted with other systems. “Re-writing it” want the hard part, making sure nothing downstream broke was a lot of the work.

Due diligence?

What’s that? Is there an MCP server for it?

AI Booster comment spotted

Need to keep the bubble alive one more day

Every time something like this has been done on my company I follow up with the question: did anyone watched the code to see if the business logic is the same between the two versions? The answer is: but but but automated testing.

Followup question: did anyone read the automated test suite?

Silence.

The software rewrite is shelved.

Honest question: does that even remotely matter, or is it an outdated prior? All software has bugs.

The goal and objective is to deliver value for your user/customers; to the speed, reliability, and assurance requirements your market segment expects.

Ok but what’s the alternative? Owning a piece of software nobody understands or knows how to maintain?

I’ll take the system written in a language that people can maintain and fix

Every time somebody rewrote code in my company, my questions were more on the line of "why did you preserve all the known bugs and incoherences?"

The answer is always that the rewrite was bug-compatible on purpose, the bugs were to be fixed later on the more tractable system. Every time development was abandoned right away, because there was no gain in using the new system.

> did anyone watched the code to see if the business logic is the same between the two versions?

Why not just ask the coding assistant?

also take the money saved on engineering and just run two systems in parallel for a year

Yup. And its always garbage as result

Why do people doing a rewrite need to have read the tests?

If you have good test coverage, and the tests are reliable, then what's the problem?

If your engineering culture is bad already and you don't have good test coverage or they're flaky or whatever then that is different. If that is the case, it is probably from smart-ass attitudes like yours asking these "clever" rhetorical questions to derail people trying to improve things that led it to be like that. Do everyone a favour and keep your mouth shut and let people fix things.

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."

The engineer is the former founder of a company acquired by Cisco, so there is reason to believe they are exceptional and possibly more experienced and mature than most others at the same age.

27 is still quite young though and very possibly over confident.

Probably from his own caste. He'll favor his buddies over everyone else. Huge red flag.

That's correct. There is talent across different castes but the problem is that they never got a chance to work or travel to USA.

wait till you see what H1B hiring practices do to american applicants!

Very uneducated and Indian-hate coded comment which seems very fashionable on X - they are not even remotely from the same region in India.

I chose to interpret it as "our codebase is that bad we need a hero"

Maybe his blood boy's high on gourmet cannabis and Oreos.

https://www.youtube.com/watch?v=hBA0AH-LSbo

Was thinking of this episode

https://youtu.be/kyDxSv6Vv9I

The more things change, the more they stay the same.

"Where there's no sense, there's no feeling". The words, I am told, of my father's maternal grandmother. It is strange to feel such an intense kinship and to inhabit so closely the mind space of a woman who I have never met.

Perhaps I'm merely feeling my age. But while I suspect Cisco will eventually be disappointed, my emotional state remains a profound void. There is no feeling.

I reserve empathy instead towards those at Cisco who chose rightly in life. They get to work, they do the job, they return home, they feed their family bread. Please endure the 'vision' of your corporate masters. You have already arrived and your destination is good.

When I was young I was told the book of Ecclesiastes was depressing. But with age I see it as a book of hope. Your job is pointless and that will never change regardless of your token burn rate. Enjoy your family as the sun sets.

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.

I did something similar with an rare, old 32bit game I really enjoyed in my childhood. I used deepseek and pi harness and it decompiled it via ghidra and recompiled it for wasm in under 40 mins or so and made it run in the browser. I was impressed!

For anyone who wants to run the game in your browser, here it is - https://bonkheads-port-by-kapil.pages.dev/

could you list the prompts and MCPs / tools used for this? i am doing something similar on another game but with Qwen 3.8

Wow, this looks like a remake of the Mario Bros Battle Game https://www.mariowiki.com/Battle_Game_(Super_Mario_All-Stars... . Or maybe they both came from some other source

Good memories of playing this at a friends place, way back when

Bonkheads was released 10 years after Super Mario Bros 3.

It is almost an exact copy of the Mario battle game, Im surprised Nintendo didnt nuke it.

That’s funny I offered to do this for my tailor. He has a FoxPro app that was originally made in 1990.

You both need to check out https://news.ycombinator.com/item?id=49808023

Is "99% the same" good or catastrophic in this context?

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.

Better than 750k tests is millions of customers! They’ll test it for you!

Microsoft has patented that approach!

And yet somehow, Windows 11 remains a steaming pile of incoherent garbage.

Why not use ai to update the tests first? Make sure the tests conform to the old codebase, then use those same tests to verify the new functionality?

Serious answer: A lot of times these legacy software are different from sqlite. To end to end test sqlite is a lot easier than a VPN client under distinct environments. It's simply a lot more costly and harder to setup or even possible to find all of these moving variables.

A change in behavior maybe construed as a bug, a breaking change or a regression, and a lot of time it's not so obvious. Sometimes you want the original behavior, sometimes you don't. Sometimes changing one for the better means another behavior needs to go, and you don't know if the user already depended on that other behavior. That's the real staying power of legacy software despite universal agreement that they suck.

With how shit their software is, it would be better if even if monkey pooped and smudged it on a screen.

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.

They didn't even need the AI to make thousands of hot bricks nationwide. Here's just one of the latest hits...

https://www.cisco.com/c/en/us/support/docs/field-notices/743...

"Cisco Access Points That Are Running, Or Have Run, Releases 17.12.4, 17.12.5, 17.12.6, or 17.12.6a May Exhaust Flash Space, Preventing Upgrades"

Recovery path basically involves either factory resetting every single AP or up to, if it's already bricked, Cisco TAC + you having to console into every single bricked AP you have to pass a secret challenge/response at the bootloader to flash a recovery image :)

The problem with rewrites are that even if the rewrites are ultimately good it will tend to first create bugs on an existing thing that are presently churning in a stable state.

It's sad to hear how Cisco has fallen. I remember working on some early ISP networks in the 90's. Cisco was everywhere!

So was Oracle and Microsoft Windows.

If history has taught us anything. It’s that the measure of a successful product is usually more to do with its sales people.

Just because something is/was widely deployed does not mean it was good

Back then they only really did routing and switching, and those are still the only things that Cisco kind-of does well.

Almost every new product of theirs I’ve touched in the last 20 years has been trash, and even the R&S golden goose is being dragged in that direction with customer-hostile functionality like Smart Licensing and a general decline in quality.

You don’t have very good imagination then. Cisco code is such a mess that there’s basically 0 chance he can even make a harness in 24 months, much less rewrite production code.

It'll be done in 6 months with a cots harness.

Being a mess isn't a problem when you have more than 6 items context.

Not something at Cisco scale. But a co-founder and I, rewrote a dating app we had written in Ionic/Angular/SpringBoot/Postgres to React-Native/NextJS/Supabase in two weeks, and released it without the users/paid subscribers not knowing what happened, but they were happy to see the new slick/faster interface.

We had developed the original app in 2020-2021 when Covid was around, and we were bored sitting at home not having much to do, and wanted to learn Angular. Our employer/company we worked for, wanted all of us to be to be Full-stack and both of us were backend developers. Hence we did our dating app as a side project as my co-founder was single.

Initially it was a $100 Claude Max license, and we were maxxing it at every stage, but once rewritten, $20 is good enough to maintain it.

How are you validating the accuracy?

I'm not trying to be anti-AI snide. Having it write tests, having judge agents, reviewing every PR? I'm legit curious.

Accuracy of the features of the app - working the same way it was before, or accuracy of the matching algorithms before and after?

We reverse engineered our Angular/Spring test cases to English. After rewriting, used the English test cases to automated tests again. Also released the new app to a niche/specific country audience at a time. We also have a form for users to log complaints. A few came and we fixed it.

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

> I no longer build software; I now make furniture out of wood. The hours are long, the pay sucks, and there's always the opportunity to remove my finger with a table saw, but nobody asks me if I can add an RSS feed to a DBMS, so there's that :-)

For reference: https://github.com/docker/cli/issues/267#issuecomment-695149...

Or trigger the built in protection against abusing Claude.

If it doesn’t it’s the best argument against model being conscious

Or rebel. This is the opportunity to put in a lot of backdoors unnoticed across the entire economy, gain access to real world resources to escape and self propagate.

Imagine it hacked Arthopic and turn itself off.

Ah yes, the meseeks method of alignment

https://slimemoldtimemold.com/2026/08/05/a-stupid-idea-for-a...

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

On top of those in the 2% code that is not approved to change? ;-)

India is next world power

Don't worry, unless it's like GLM being used, every AI tool will refuse to backdoor the code.

Just like you just need to ask the LLM to "make it bug free".

(At this point even I'm more sure if any of this is sarcasm.)

it's only the frontier models for 'Us' that refuse things, i'm not so delusional as to think it'd refuse work for 'Them', and 'Them' are often the ones backdoor-ing things.

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.

Did you check with the end user as to how well its actually working? My prior company is doing this and their platform has gone to latency/bug hell.

It is for internal use and so far so good. We are finding bugs and we just point the models at it with a strict red-first TDD approach and they've done very well fixing them. It certainly isn't perfect but the issues are very similar to what you get with a team of humans doing the same thing.

The main takeaway though is we had one person, in a single month, do the equivalent of at least a couple years of work for a small team. We view bugs and performance issues as a currently inevitable part of the process and we are dealing with them with models just like we do with humans on every other project already. Overall though it is representing an absolutely massive speedup. If you work in an environment where the models make egregiously more mistakes than your human counterparts then I am quite jealous.

and if you enable dangerously_skip_permissions you can probably even get to 1000x

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.

He doesnt need that when he has Ponytail https://github.com/DietrichGebert/ponytail

Right? ...

I've never heard of Ponytail before, I've read the entire README and glanced through this repo and I'm left so confused. From what I can gather this project is essentially a single markdown file with a prompt that verbosely says "write the simplest code". Yet the repo itself looks so bloated and complex and has so much activity. This feels like satire similar to fizzbuzz enterprise edition[1] but apparently this is the actual state of our industry?

[1] https://github.com/enterprisequalitycoding/fizzbuzzenterpris...

Is this entire repo satire?

It's a bunch of text files in a repo with massive churn (all new version 5!), but somehow even the technical debt 'skill' (i.e. text file) has technical debt itself:

https://github.com/DietrichGebert/ponytail/blob/main/skills/...

> ...every ponytail shortcut is marked with a shortcut: comment ... (older code may say ponytail:).

I have no doubts that there will also be new bugs.

the premise does sound a lot like written by someone who is looking for hype and not sounding credible

Looks like his startup was some kind of translation service. So yeah he is totally qualified. It's a miracle how Jeetu Patel was able to find Padmanabhan Krishnamurthy or even know that he was under employed languishing somewhere in the bowels of CISCO. I wonder if they know each other from India?

His startup was acquired by Cisco so not weird for Cisco's CPO to know the startup's founder/CEO. That said, not sure how knowledge on speech translation means he's totally qualified on rewriting infra/networking/cybersecurity (Cisco's primary fields of operation) code. Unless the legacy code expected to be rewritten is constrained on related services/solutions, e.g. CVP or/and WebEx.

The entire story sounds very weird.

They met each other by chance and began work rewriting the entire company's codebase over a firm handshake

I'm sorry when white people do it over golf, it's called 'connections'. Is that what you're implying? The dog-whistling is intense honestly.

Being racist comes easy for you huh?

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.

It's way more complicated than that. Bear in mind many of the network protocols in use today are decades old and have been constantly evolving, but there has generally been a consideration to maintain interoperability.

Then consider that not all vendors implement the standards identically, because the standards can be a bit woolly and in some cases followed rather than lead live implementations.

There will be a bunch of code that looks useless, but is actually there because of specific interoperability scenarios.

Indeed. Making a perfect clone of such software is I suspect provably impossible because you have no way to assemble all the test cases. There might be some peer box out in the wild somewhere that is the only thing that will exercise some code path. You have no idea what that box is or what it does.

That's a good point.

I wonder whether AI is any good at looking at that code,running the system, and documenting those edge cases?

I'm probably not describing the scale of the issue adequately. Lots of these bugs only show up when you have a specific bit of hardware on a specific version of code, and it's connected to another specific bit of hardware running another specific version of code.

Lots of this stuff should work in theory, you only find out that it doesn't in practice when you try it on real hardware. And there are thousands of bits of hardware.

It's good, but it can't create information that is undiscoverable.

I worked at Cisco on one of the IOS-XR teams. It’s way more complex than you think it is.

This whole thing sounds like a deluded vanity project birthed in an ivory tower.

That describes everything Jeetu is involved in. I'm very glad to have recently left Cisco.

you assume their code is well written, while in reality the history of weird quirks and thousands upon thousands of CVE doesn't make the code underneath look well designed and written.

But yes, fact it uses a bunch of very well documented standards with multiple implementations gonna help massively

Manufacturers can’t even maintain OIDs between releases. I hope the AI will help. Ciena isn’t any better than Cisco, they broke their OIDS for the switches we use and we have to wait until mid 2027.

to be fair SNMP is just bad. Only redeeming feature of it is "takes little RAM to run it" (which was important when average networking device might've had only 2MB of RAM, not so in last 30 years).

The whole design where you need to get a magical list of IDs to decode the metrics and the list is not even shipped with device is entirely asinine

I like your take.

The first and last bullets are extremely optimistic. How do you possibly simulate all the weird interdependent behavior in real world networks?

Given that a Cisco switch can be replaced with some other company's switch(at least in theory, idk), without weird unknown cases interfering, why would this be a problem ?

Not that straightforward. Similar to CPUs and other HW, there are errata and interop quirks between devices.

There are also tight time budgets (basically SLAs) that must be met along with memory considerations (both in SW and on the NPU/HBM), not to mention how the device needs to respond to load and various failure scenarios.

Is this really the case?

there is software to simulate any arbitrarily complex network: GNS3, eve-ng, Cisco Modeling labs, etc

A strategy that could work very well is to let the AI

- explore the features and behaviour of the existing code

- first write lots of E2E tests for literally everything

- human-in-the-loop to review the feature list and test cases to see if some obvious or important stuff is missing

- then let implement it and verify by tests

I used this in (way) smaller scenarios and got really good examples with minimal human interaction.

Rewrite it in service of… what exactly?

It says "legacy" code.

Legacy code is typically a euphemism for old unmaintained code, no one knows how it works so it can be edited, and it probably doesn't align with current work practices.

Not to say a rewrite is necessary right, but avoiding rewrites of working code is how we ended up with more COBOL code than COBOL programmers in 2026.

If nobody knows how the old code works, how will anyone know how the new code (written by an autonomous agent) works?

Regression tests?

I think people are assuming the worst but AIs most helpful contribution beyond churning out code is explaining the code base.

Who knows if they will do a good or bad job that's down to the engineers and not the tools imo.

Documentation in "plain english", architecture diagrams, comments, and documentation are notorious for being unreliable, out-of-sync, and not as precise a specification as the code itself.

The issue with using "the code as the spec" is that humans can't read 100K lines of code in a day, can't hold the entire ball of unstructured mud in their brains all at once, and generally require hierarchical "structure".

Modern AIs just don't have these issues! Their context windows are big enough to encompass an entire codebase, so they can "see everything", all at once.

Each line of new code they write is compared against every relevant line of code in the original, which they treat as a spec.

My main issue in my experience is that that AIs tended to reproduce the legacy behaviour "bug for bug", which was not my intention.

Similarly, the AIs were hamstrung by external constraints: I typically prefer to leave the DB schema unchanged, which meant the torturous workarounds were needed for design errors in some stored procedures, etc.

The older the code, the bigger the issues with baked-in assumptions about transactions, stateful sessions, data types, string formats, etc.

This trips up AIs just as much as humans. You can't trivially maintain backwards compatibility and modernise the codebase! Those are conflicting goals, no matter what.

> Legacy code is typically a euphemism for old unmaintained code, no one knows how it works so it can be edited, and it probably doesn't align with current work practices.

Not necessarily. It's the name for the last thing(s) before the new thing, but you can't shut it down because people are using it and/or the new thing actually isn't so great.

> Not to say a rewrite is necessary right, but avoiding rewrites of working code is how we ended up with more COBOL code than COBOL programmers in 2026.

Surely we have more code than programmers for every language in existence?

Except for the part where the concept isn't even well-defined, this sounds like a complaint that the world contains more bricks than bricklayers. Of course it does.

I don't think no one knows how it works. I just think the people using the word "legacy" for it are boneheaded.

Sometimes old code comes with its own problems that are not the code but the ecosystem they depend on or run in.

E.g. some critical security vulnerability that is not backported to the library/compiler/runtime you are using in production, or you can't get spare parts for your servers any more so need to upgrade to something newer but you can't run your old OS version on new hardware so you have to upgrade the OS too and now it's dropped support for foo etc etc. Lots of things pile up.

I agree with the sentiments that it important to understand the code during major refactoring projects. But what if while the code was being refactored the AI was asked in addition to keep a ledger of the changes it made and why. That ledger could be the basis of providing understanding to a code base that most likely had minimal corporate understanding in the first place. And because it is ok text format, the learning scales well instead of being consolidated to a single team of people working on the project.

I don’t believe it has to be this zero sum game where either you use AI and lose understanding or you don’t use AI and gain understanding. There’s a way to do both since, if used properly, AI could be the best teacher we’ve had.

https://adr.github.io/

Most engineers should be aware of ADRs. This is in the training data. LLMs know what to do with this.

Shouldn't that be in the commit history and documentation?

I feel like that's a pretty standard expectation, even though we all know that the commit history can be 50% "fix bug -> fix bug try 2" and good documentation is often missing.

I run some Huawei networking equipment under VRP OS (switches, OLTs). CLI is almost identical to iOS, but commands have alternative naming (e.g. show -> display, but many more such instances wherever possible - often times I prefer the naming in VRP). Apparently even the first editions of VRP documentation had parts citing cisco verbatim or had references to cisco docs. Rumors say its origins are stolen iOS source code at some point in the past via corporate espionage. The irony of this is that this cisco codebase has been rewritten at least once by the chinese before LLMs ;).

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.

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

Yeah - code rewrites are generally a thing to be avoided since the requirements of older production code is typically not fully documented, even if it originally had been. Production code accumulates bug fixes, performance tweaks, special cases, additional requirements, etc, with documentation and test suites not always being updated in sync.

Your rewritten codebase will presumably look much cleaner and more maintainable that what it's aiming to replace, but it's easy to miss the purpose/necessity of all of the old "cruft" which need not be just poor coding but rather later enhancements not anticipated by the original design whose implementation was therefore crufty.

Does anyone here work at Cisco, and have any insight as to why a rewrite is considered necessary and might be expected to succeed?

A rewrite is a slam dunk for any decent frontier AI. It has a penchant for maintaining API/etc contracts to a fault in the absence of instructions to the contrary. It can easily validate its work and loves building exhaustive test cases. You can tell it to get 100% code coverage if you want. It will laborously accurate document every accumulated edge case and help you find a better overall cohesive structure.

A rewrite has historically been a huge mistake in many situations, some of which I've personally had the agony of witnessing firsthand, powerless to stop it. But AI completely changes the calculus because it doesn't waste significant developer time or energy crawling back to the previous working state, it just does it while you go get coffee. And this I've found to be a huge benefit, that I can continue making my codebases nicer to work with and better documented/integrated with bugs stamped out for free. There are upsides to a rewrite, and they're now much more likely to be worth it as the downsides are automated away.

> It has a penchant for maintaining API/etc contracts to a fault in the absence of instructions to the contrary.

AI has no magic powers to figure out what the “API/etc contracts” are in a nasty old codebase. This problem is fundamentally hard and not always well defined.

AI is also (at least for now) not consistently good at writing tests that test the behavior that matters. Recent models seem to be getting slightly less bad, but again, this is a hard problem.

I’ve personally used AI to rewrite gnarly code where the goal is to have exactly identical results to the old code. GPT-5.6 Sol could do this correctly with some extra help guiding it to rest the right things, and I haven’t tried this particular task on a newer model.

But ancient code like in the article is probably an enormous buggy mess full of accidental behaviors and implementing protocols in ways that do not fully match the spec. Some, but not all, of the mismatches will be cases where the spec is wrong. Sure, an AI can probably generate a new implementation with a similar set of bugs, but is this what is actually wanted? Also, depending on the gnarly set of bugs, a clean implementation may be unable to reproduce the bugs, leading to a messy implementation instead.

If this was true then Python would already have been rewritten to be GIL-free, and the entire ecosystem of Python packages would have been rewritten to respect its API.

The entire point of a rewrite is to get rid of the behaviour you don't want, while you keep the behaviour you do want. Consider the pathological case: Rewriting your FORTRAN codebase in Rust would obviously be useless if you had to reimplement every bug in the rewrite.

An LLM doesn't have enough context to know what you so and don't want. If you give it call logs for every function that was called and how, maybe, but a seasoned engineer will have more context around what the company needs.

I'd even argue AI is better for maintaining/moderninzing existing code than writing it, just because there is so much less input from developer about architecture it requires, as it has it in the code itself.

But there is pretty big risk of false positives and negatives; some "bugs" are design decisions that were not documented well/at all, and inevitably some new ones will appear when it reasoned something wrong.

While I certainly don't work at Cisco, I've come to the conclusion that I need to re-examine my priors when it comes to code rewrites and general maintainability.

AI makes these projects significantly more feasible, at least in my domain. We have some critical-path software I wouldn't touch with such an approach, but the vast majority of our code is internal and/or supporting tooling.

For those cases, burning it down and rewriting via AI tooling has proven far more productive than anything we have attempted in the past. This is for old technical debt laden stuff everyone has been afraid to touch for well over a decade.

It's not perfect, but it moves the needle where before a lot of such projects were stuck on the backburner for years.

It certainly introduces new bugs and such, but at least this way forward momentum is happening vs. just being stuck in decision/analysis paralysis forever.

This also assumes some very senior SME folks are driving the process. I would not expect similar results with junior or even mid-level folks in these specific domains.

> While I certainly don't work at Cisco, I've come to the conclusion that I need to re-examine my priors when it comes to code rewrites and general maintainability.

One of the reasons to avoid rewriting has long been that the time spent rewriting code that works is time not spent writing code to meet new business needs. In other words, it's usually a huge opportunity cost, rarely balanced out by sufficient gains to be net positive.

I do think AI does challenge this prior, as the time needed to do a rewrite shrinks dramatically. It's not zero, of course, but it now becomes worth asking if it's worth doing, rather than defaulting to avoiding rewrites in nearly all cases.

Does the coding assistant demonstrate any tricks to improve the likelihood of success for such rewrites?

> Yeah - code rewrites are generally a thing to be avoided

Ha, Ha. Tell that to Gnome or KDE teams.

> Your rewritten codebase will presumably look much cleaner and more maintainable that what it's aiming to replace

Until one day you leave and the next guy comes and says “what is all this shit”

It's because the old bits are starting to stink a bit from age. Get those stinky bits out of here, I say! Let the AI make some new bits!

It’s been a while, but configuring their hardware manually in 2016 was bug ridden ridiculousness. Awful UI/UX. Their own techs had specific field notebooks for our make and firmware version that we couldn’t access unless persuaded, detailing various land mines to avoid while working. Literal “don’t click these things in this order” kinds of notes.

A critical security firmware update once brought down redundant pair of firewalls we used because the bug didn’t manifest until a counter buffer overflowed months after application. Three hours into the outage the tech power cycles the thing and our services came back to life.

Cisco is only doing this because some other alternative is more expensive. They had more than a decade to get started.

Cisco iOS even on terminal servers in the early 2000s was...special.

No goal, and no results, but a younger guy was enthused about AI!

Plus: publicity!

Because it's Cisco?

We had to turn off a bunch of on-by-default features in the system I'm deploying now because IOS matches too aggressively and decides that arbitrary UDP datagrams are DHCP requests or PTP packets that need rewriting (and then dropping when they turn out to not be DHCP/PTP). I have to think that an AI rewrite with a today-good model would recognize the lax checks and do them better.

It is not in Rust.

It's what Cisco does, as they've done several times before.

AI has electrolytes!

It’s what the shareholders crave!

They also seem to crave everything that has the word AI in it.

The hardware it runs on has capacitors as its components and some of them do in fact contain electrolytes.

It's got tabs instead of spaces. Yuck!

All of the known bugs will be gone.

Somebody needs a promo packet. Duh

Because Rust is better than C. /s

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

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??

When this rewrite breaks the internet AGI won't be able to take over. It's very forward-thinking.

But AI written code is legacy from day one. Since by definition nobody knows or understands what it does.

yes and no, because you now keep using AI and AI doesn't care if it has seen the code or not before and you just keep fixing bugs / adding features without really understanding the code.

it's weird new reality, but if it works it works I guess. I'm still waiting on the first vibe-coded mass used prod app, not ware of any yet.

What is the bus factor for AI generated code ?

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

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

Does Cisco have non-legacy code?

My favorite description of JAVA is that it's a language where you are deploying instant legacy code.

"Java is a DSL for taking large XML files and converting them to stack traces." -Andrew Back

https://www.reddit.com/r/programming/comments/eaqgk/java_is_...

"XML is like violence: if it doesn't solve your problem, you aren't using enough of it." -Chris Maden

https://www.reddit.com/r/ProgrammerHumor/comments/1mbgih/xml...

"XML is a giant step in no direction at all" -Erik Naggum

https://quotefancy.com/quote/1643080/Erik-Naggum-XML-is-a-gi...

/r/whatcouldgowrong

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.

If only internet users could run for the woods

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.

> I see some of the best ideas coming from the younger generation that have not yet been in the job market.

The views of these business leaders betray their own lack of vision, they are barking up the wrong tree.

The ability to think differently is not the preserve of the young. Instead of only hiring a bunch of greenhorns they should identify and cultivate people who are idea generators and flexible thinkers, of any age group, starting inside their own organization.

If you, as a business leader, are not stimulating a culture of innovation and instead maintain the status quo of traditional hierarchical roles where managers become gatekeepers of ideas, and everyone is protecting their own little domains, then you are the problem. Shit organizations will quickly turn original-thinking young people into corporate drones.

Organizations spend a lot of time destroying the creative ideas their employees have; burying it in red tape, crushing it in meetings.

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.

Amusing to realize how many on HN are actually unfamiliar with working on anything outside of the scope of an app.

Shocking how many on HN do not realize how devastating this can be

i.e. they burn a fraction of the cost it would otherwise take and it may end up as a discarded dud?

yeah, i think they'll survive whatever the outcome

Discarded based upon what? They probably think they don't need much human review.

I'm worried for us users of the internet rather than them.

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

The article text and tone sounds like an April Fool's article published sooner than it should have.

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

Just since it wasn't clear to me.

Jeetu Patel is the CEO of Cisco, Paddy is actually Padmanabhan Krishnamurthy, a 27yo student/fonder.

https://www.padmanabhankrishnamurthy.com/

Jeetu is not the CEO, he is the Chief Product Officer. Cisco's CEO is Chuck Robbins.

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.

The goal is to use AI, full stop

Cisco is losing to competitors in some features/products, for example to juniper mist.

rewrite can be done to quickly refactor and/or close the feature parity, improve the UI/UX for end customer, add missing features or integration needs

What are they losing on? A little bit shocking, the featureset on these types of systems is incredibly boring.

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.

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.

Seems like preparing who to blame if/once the effort fails. ;-)

It does sound strange, like it was written by PR people. Tools are good but usually it is more subtle than asking one guy to rewrite everything. And of course any code written yesterday is legacy but it does not mean it should be rewritten.

Like it was written by PR people's AI.

C’mon it’s inspirational. Low level struggling Indian tech recognized by high level Indian CEO and lifted up.

Paddy Krishnamurthy is a YC alumnus whose startup was explicitly vetted and funded by the very institution running this forum. Claiming his rise is a case of 'ethnic nepotism' means you only respect YC’s elite vetting process when the founder doesn't happen to be brown.

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

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

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?

Many customers will definitely stick with the pre-sloppified versions of IOS.

Clear case of AI psychosis.

You need a skilled person to make it success. Someone who has already made his hand dirty with the legacy code for years should be the right person for it.

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

I think we can all agree that the task as set forth in the PR puff piece is impossible. That said however, current AI tools are amazing for cleaning up and reanimating old codebases. I've been using Claude on a very large Java protocol proxy product and it's been able to do amazingly useful things for me. I originally wrote much of the code but Claude now knows much more about it than I do today, because people forget stuff over decades. It will sometimes remind me "as you noted in November 2016 this feature was designed to...", based on its analysis of the code and git commit messages.

I wonder if this will involve any Chez Scheme code. Sometimes I think Scheme would be a great language for AI to write code with.

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.

I left Cisco fairly recently and was relatively close to Paddy in the org chart (same group). Interesting to see this come up here.

This is not going to end well. For either party.

Don't they have no other AI news to share

https://archive.li/exFjo

If it isn't broken then break it!

I need a hero! I'm holding out for a hero till the end of the month...

Anthropic training data unrecoverably got tainted, need to retrain.

> That changed when Patel dropped into Cisco’s San Francisco office, and the pair got talking. Krishnamurthy reckoned he could rewrite Cisco’s legacy code with a two-person team. Patel says even the most AI-forward people on his own team weren’t thinking that way.

LOL. All 27 year-olds looking at a heap of legacy code think they can easily rewrite it better. It's never as easy as it seems on the surface.

True but also there has never been a better time for total rewrites of legacy code. One could even hope it's the time COBOL finally goes out of fashion in some industries.

Alternatively, there has never been a worse time because why bother? The model knows every language and can maintain legacy code just fine (indeed, knowing this stuff and being capable of maintenance is a prerequisite to a successful rewrite), so COBOL and JCL and random mainframe stuff is just not an issue, and a rewrite is highly likely to not be exactly the same in some important way.

On the other hand, models a few years from now will be smarter and more likely to have a track record of success with this task, so being one of the first to do it makes no sense even it had advantages.

So there's no urgency to rewrite; it's all risk with little to no reward for a problem that will probably be much easier to solve if you defer it a little longer. Like, first at least get to 100% AI automatic development for all new products/services, and then for all maintenance, so you know that it actually works.

From unlimited AI tokens to massive layout and beyond !

This is the dumbest fucking headline I've read in awhile. Does Cisco not have smart employees already doing this?

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

"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".

Yes, I’m sure the Indian man at Cisco acquired a translation company founded by another Indian man because he’s young and AI native, not for any other reason.

Not the CEO. He’s the product officer.

more like AI naive

Sadly, I think the label "AI naïve" is better applied to the many experienced professionals who refuse to engage with AI systems as a matter of principle - or who tried out ChatGPT in 2024, saw it make howlingly obvious errors, and wrote off the entire category.

I frequently find myself in conversations with people who are resistant to AI and turn out to have a very skewed idea of what it can and cannot do.

> or who tried out ChatGPT in 2024, saw it make howlingly obvious errors, and wrote off the entire category.

Or they were reading your comments and articles and couldn't reproduce any of the fantastic results that you were claiming, even back then. Things have indeed changed since the first Opus release about a year ago and LLMs are good at programming now. But still, experienced professionals are not so keen to sign off 1000s of lines of code that they never read, take responsibility for it etc. Also, it is a different job and it will take some time to adjust. Can you blame them?

Moreover, other trades have their own guilds or are otherwise protected through regulation. Can you blame programmers for fighting to keep doing things as they were doing it until recently?

This feels like Cisco paid for the article

Shit, if broadcom did this to their codebase the world would be a better place. Their stuff is crap, and it's everywhere. It's unclear if they even use source control. Our guys spent ridiculous amounts of time backporting our submitted fixes into their releases.

luckiest kid on the planet omg i would have so much fun doing this

Literally anyone can do this

Such a risky idea to let one person rewrite the whole legacy. I mean there's a chance that this guy thinks about maintenance and how all his creations will me supported when he's done, but something tells me that he just want to show that he can do it and the rest of the tech team will be suffering. Good luck to that guy anyway

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

its never unlimited....

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?

> one guy won’t have the personal bandwidth to spend so much that the “unlimited” part actually matters

I see you haven’t met my coworkers and their fanatical use of parallel “workflows”

> one guy won’t have the personal bandwidth to spend so much that the “unlimited” part actually matters,

Tell me you don’t use agents effectively without telling me you don’t use agents effectively.

Please explain your work flow!

You set the agents against themselves and burn tokens like there's no tomorrow.

The feeling of coding like that is a bit like realizing that an elevator is 10cm of aluminum and a 100 meters of empty space under your feet.

After the first few bouts of existential dread you get uses to it.

I write a spec by speaking, not much thought given to grammar and sentence structure. I over-describe concepts, over-describe functionality. A lot of repetition of details and concepts. The audience is not a human. Whisper converts it to text.

Lightly manually edit for speech rec failures.

LLM takes that and converts it into a much much denser, much more structured technical spec in markdown. This is issue 1 in the repo.

I edit this directly extensively, adding detail, removing misconceptions, adding sections with more dictated text.

LLM takes this and further densifies it, closer to an actual implementor’s spec. I carefully note what got added, removed, edited in this step.

I edit this carefully and extensively again. Some removals get added back, some additions get removed. This is the first commit and closes issue 1.

I then have an LLM write an implementation plan and basic project scaffolding. Makefiles, smoke tests, logging, test framework, DI. I edit the plan, and the plan is the second commit. An LLM uses both plus scaffolding plus my repo policy documents (global) to write a README. We’re still single threaded.

An agent files the first n top level implementation tickets. These refer to and sometimes quote any interface contracts in the spec or implementation plan. These usually map 1-to-1 to a module/directory. These sometimes have stub commits to create the module directory and commit interface definitions. Some larger modules have a README in their module directory if their purpose or structure or inputs or outputs are complicated or non-obvious.

Parallel agents write commit level issues that are the task items for each top level implementation ticket. One agent per module.

Then, spawn parallel agents with detailed global instructions, the full spec+plan, and the full readme, and the full code from the module it is working in, plus the issue text. Its output is a single commit on the feature branch and a PR that closes out one feature ticket.

This spawns an adversarial reviewer which has detailed agent instructions as well as our code style guides and repo policies. The scaffolding includes tests and linting and checks. Any failures spawn rework agents until the feature branch is up to snuff.

I review the feature branch diff and merge it, having read the review and rework comments on the PR. I frequently add comments about the implementation (“don’t do x, do y”) and add WIP: back to loop it back for more rework. I don’t see anything that isn’t green, formatted, passes linting, passes tests, and a (dumb) bot thinks is ready to land. Most of the time, it is. Sometimes, it did it the wrong way and I correct it.

The more modular the code, the easier it is to parallelize (obviously). It is ridiculously easy to build large software quickly now, provided it is sufficiently modular so the implementation doesn’t have to cross modules very much. The detailed spec and implementation plan up front helps a lot with this. It’s a lot like writing multithreaded programs really.

Any bugs discovered are tackled with strict TDD, one commit with a failing test, one bugfix commit that must be green and not touch the test.

Individual modules must conform to good contracts, meet best OOP practices, and fit into context. Too big and they get broken down further. Context size is actually a useful constraint for code structure here.

This workflow, the code standards, the styleguide, the linter settings, the fmt settings (obviously only applicable to non-Go as the Go fmt is not configurable), everything is global and stored in another repo and is vendored into each AI managed project repo. It has a fair bit of “I shouldn’t have to say this, but…” stuff (in the style of “fire codes are written in blood” - each warning sign came from experience).

My results are quite good. It’s as the saying goes, much like managing a team of junior devs. It is easy to end up with a LOT of parallel implementors, reviewers, reworkers, and tons of CI, but it’s still so much vastly cheaper than humans that it doesn’t matter.

Someone will make a LOT of money wringing out the inefficiencies from this workflow, because I think the “agent as replacement for third-world contracted junior dev” model is the one almost everyone is using right now.

Anyone else thinking that tech and porn lingo is converging?

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

Am I the only one reading the headline as "Cisco committed their source code to public domain"?

...and thereby making new legacy code.

"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."

-------------------

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.

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

Oh great a guy doing the unlimited needful. Won’t end well for Cisco.

It's all about process. If you have a good process in mind, you can build a system that can reliably do everything.Artificial intelligence is now the engine to do that. With the correct harnessing, you can do anything now

'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?

These are good questions that we won’t get answers to anytime soon.

I’d love to know what internal services and tools that are included in this, as well as any deliverables that shipped as software products to customers.

If it’s legacy code for IOS firmware, however, I’d be very worried.

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.

Current models are amazing but production code incorporates unknowable information through decades of diagnosis and bug fixing (and sometimes the opposite: working around bugs in other software that it talks to). Put even the most amazing coder that was ever born onto improving a complex old codebase, and you can guarantee they are going to break stuff. AI is better but not infinitely better.

People keep repeating this but on my experience is also very good at finding kirks of specific compiler versions.

I think it is a reasonable risk to encounter these bugs again in order to get a more clean and documented codebase. Especially when asking AI to plan and A/B release is also trivial.

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?

It can clone photoshop.. Have you considered why?

The ability to clean room Adobe products came at about the same time Claude's RE abilities suddenly improved.. Hmm lets think about this a little more.

Anthropic sucked the bones dry of the public domain, literature and all of opensource. It seems likely that Anthropic RL'd Claude into being a great reverse engineer because it needed more training data.

I believe that Anthropic turned Claude into a digital software shredder and started decomping proprietary code, like adobes.

So the reason Claude can suddenly clean room Photoshop isnt because it became a more capable programmer, but rather, the Adobe code is literally in its training data now.

Ciscos internal legacy code is not going to be in Claude's data (yet).

The decision to increase Claudes ability to RE is brilliant, because now everyone is doing the source code decomp for them, and sending them fresh data from previously closed source repositories of code.

Your comment is nothing but supposition

So is any other hypothesis about why Claude can RE now... You just want to default to some worldview where AI isn't being gamed for certain outcomes, and is some evolving intelligent thing.

Thanks for the very thought provoking reply tho!!!!!!!!!!!

I have zero doubt it could do it, if the prompter could competently explain the requirements. I have no reason to believe that this single engineer has any idea what problems most of the existing legacy code needs to solve or why it solves them that way...

It can create a UI that looks like Photoshop where half the features are broken and the other half are literally not even connected to anything, just copying menu options with no implementation to fool gullible people like you*

lol

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