Launch HN: Hypercubic (YC F25) – AI for COBOL and Mainframes

Hi HN, we’re Sai and Aayush and we’re building Hypercubic (https://www.hypercubic.ai/)!

Hypercubic is an AI platform that helps Fortune 500 companies understand, preserve, and modernize their mainframe systems. These are the systems that run COBOL from the 1960s that still quietly power banking, insurance, airlines, and governments today.

70% of the Fortune 500 still run on mainframes, but the engineers who built and maintained them are retiring. Today, the average age of a COBOL/mainframe engineer is about 55 and rapidly increasing. What’s left behind are opaque, black box systems with almost no one who understands how they work. Modernization projects often fail, documentation is decades out of date, and critical institutional knowledge lives only in the minds of a few senior subject matter experts who are now leaving the workforce.

Current “AI for code” tools focus on codebases and repositories, so they miss the unwritten rules, historical context, and architectural reasoning that live in human minds. In the COBOL/mainframe world, that institutional knowledge is the key missing piece.

What we heard from modernization leaders is that the hard part is not the code analysis. The challenge is the institutional knowledge that never made it into code or documentation and has walked out the door. Modernization projects fail not because no one can parse COBOL, but because no one can answer “why was this billing edge case added in 1995 and what breaks if we remove it.”

Hypercubic is building an AI-native maintenance and modernization platform that learns how legacy mainframe systems actually work and captures the human reasoning behind operating them. We’re doing this with two initial tools, HyperDocs and HyperTwin.

HyperDocs ingests COBOL, JCL, and PL/I codebases to generate documentation, architecture diagrams, and dependency graphs. Enterprises currently spend months or years hiring contractors to reverse-engineer these systems; HyperDocs compresses that work to take much less time.

COBOL was designed to resemble English and business prose, making it a good fit for LLMs today. Mainframes have decades of consistent patterns (COBOL, JCL, CICS, batch jobs) and a finite set of recurring tasks (such as payroll, transaction processing, billing).

For example, here’s a billing fragment that would be run nightly in production at large insurance companies for moving money, closing accounts, and triggering downstream reports:

  EVALUATE TRUE
      WHEN PAYMENT-DUE AND NOT PAID
          PERFORM CALCULATE-LATE-FEE
          PERFORM GENERATE-NOTICE
      WHEN PAYMENT-RECEIVED AND BALANCE-DUE = 0
          MOVE "ACCOUNT CLEAR" TO STATUS
          PERFORM ARCHIVE-STATEMENT
      WHEN OTHER
          PERFORM LOG-ANOMALY
  END-EVALUATE.

Now imagine thousands of these rules, each running payrolls, processing claims, or reconciling accounts, spread across millions of lines of code written over 40+ years. HyperDocs ingests that code and reconstructs it into readable, living documentation that shows how the black box system works.

Our other tool, HyperTwin, tackles the “tribal knowledge” problem. It learns directly from subject-matter experts, observing workflows, analyzing screen interactions, and conducting AI-driven interviews to capture how they debug and reason about their systems. The goal is to build digital “twins” of the experts on how they debug, architect, and maintain these systems in practice.

Together, HyperDocs and HyperTwin form a knowledge graph of legacy systems linking code, systems, and human reasoning.

Here’s a demo video of our HyperTwin product: https://www.youtube.com/watch?v=C-tNtl9Z_jY

You can explore our documentation platform, including examples from the AWS Card Demo (a widely used COBOL codebase example) and a dummy insurance project here: https://hyperdocs-public.onrender.com/.

e.g. Developer perspective docs - High level system architecture of credit card management: https://hyperdocs-public.onrender.com/docs/aws-carddemo-with...

We’re curious to hear your thoughts and feedback, especially from anyone who’s worked with mainframes or tried to modernize legacy systems.

I'm excited for you but nervous about the kinds of bugs that might get caused

Yeah, we've heard the same "big bang" story a bunch of times as well. However, step 1 (extensive test suite) is often missing and is something you'd have to do as part of the modernization effort as well. Overall, it is a pretty hairy and difficult problem.

This is weird. Mainframes are the dinosaurs of tech. Never would I think, 'let's add some AI' to a mainframe. It would be like adding opposable thumbs to dinosaurs. You are still solving the wrong problem, but it sure will be interesting watching the systems cope.

IIUC, what's being solved here is not the mainframe, it's the lack of knowledge transfer of what the heck that software is doing and how it works. Anything that drives down the cost of answering those types of questions, whether for debugging or replacing, is going to be worth a lot to the dinosaurs running these systems.