Migrate legacy COBOL to Java with agents and prove the outputs match
In a 50-minute live demo, Anthropic's Claude Code team migrated legacy code with agents: Opus 5.5 moved about 700K lines in under a day, pulled 323 business rules out of 44 COBOL programs, caught a money-moving security hole and ran COBOL and Java side by side to show the same output. They also showed a 500K-line Java 8 to 17 upgrade.
Source
@0xShoopy on X · 2026-10-02
Written in our own words. Credit to the original author. Link checked 2026-10-22.
What they did
In a 50-minute live demo, Anthropic's Claude Code team migrated legacy code with agents: Opus 5.5 moved about 700K lines in under a day, pulled 323 business rules out of 44 COBOL programs, caught a money-moving security hole and ran COBOL and Java side by side to show the same output. They also showed a 500K-line Java 8 to 17 upgrade.
Result (as claimed)
Their point: writing the code is now the easy part; finding and checking the business rules is the real job.
Tools they used
Cost: Claude Code: from $17/mo; Claude Opus 5.5: from $4 in / $20 out per 1M tokens.
Set it up
Pick a contained repo or task
Start on a branch or side project where mistakes are cheap.
Install and configure
Set up Claude Code, Claude Opus 5.5. Read what it can run on your machine and limit permissions where possible.
Run it on a real task
Give it a well-scoped issue and let it work. Review the diff like any pull request.
Add guardrails
Keep tests and CI in the loop, and never let an agent push to main or touch production secrets unattended.
Copy the full setup prompt
Paste into your agent and it will walk you through the setup, asking before anything that sends, posts or spends.
You are helping me set up this AI use case end to end in Claude Code. Goal: Migrate legacy COBOL to Java with agents and prove the outputs match What the original author did: In a 50-minute live demo, Anthropic's Claude Code team migrated legacy code with agents: Opus 5.5 moved about 700K lines in under a day, pulled 323 business rules out of 44 COBOL programs, caught a money-moving security hole and ran COBOL and Java side by side to show the same output. They also showed a 500K-line Java 8 to 17 upgrade. Reported result (as claimed by the author): Their point: writing the code is now the easy part; finding and checking the business rules is the real job. Source: https://x.com/0xShoopy/status/2106011831227539477 Tools they used: Claude Code, Claude Opus 5.5 Category: Dev & ops Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
You are helping me set up this AI use case end to end in Codex. Goal: Migrate legacy COBOL to Java with agents and prove the outputs match What the original author did: In a 50-minute live demo, Anthropic's Claude Code team migrated legacy code with agents: Opus 5.5 moved about 700K lines in under a day, pulled 323 business rules out of 44 COBOL programs, caught a money-moving security hole and ran COBOL and Java side by side to show the same output. They also showed a 500K-line Java 8 to 17 upgrade. Reported result (as claimed by the author): Their point: writing the code is now the easy part; finding and checking the business rules is the real job. Source: https://x.com/0xShoopy/status/2106011831227539477 Tools they used: Claude Code, Claude Opus 5.5 Category: Dev & ops Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
You are helping me set up this AI use case end to end in Grok Bot. Goal: Migrate legacy COBOL to Java with agents and prove the outputs match What the original author did: In a 50-minute live demo, Anthropic's Claude Code team migrated legacy code with agents: Opus 5.5 moved about 700K lines in under a day, pulled 323 business rules out of 44 COBOL programs, caught a money-moving security hole and ran COBOL and Java side by side to show the same output. They also showed a 500K-line Java 8 to 17 upgrade. Reported result (as claimed by the author): Their point: writing the code is now the easy part; finding and checking the business rules is the real job. Source: https://x.com/0xShoopy/status/2106011831227539477 Tools they used: Claude Code, Claude Opus 5.5 Category: Dev & ops Please: 1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like). 2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure. 3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data. 4. Finish with a checklist to run it again next time.
The Daily 5
Get five new use cases tomorrow morning
Free. Real sources. Unsubscribe any time.
Guides for this use case
How to port code to another language with AI · How to vibe code an app with Claude Code · How to compare AI models on the same prompt · How to secure vibe-coded apps and agents
Related use cases
Turn a spare Android TV box into an always-on host for your AI agent
A builder had Claude Code inspect the Android TV box from his TV provider from a prompt and one photo, install a Linux shell built for its chip, add a wake lock and battery whitelist so Android cannot kill the agent, and wire the agent to his own Telegram bot with no open ports.
Run cheap DeepSeek Flash workers inside Claude Code with Opus as the boss
A builder plugged DeepSeek Flash into Claude Code as the worker model and kept Opus 5.5 as the lead that plans and checks. He cites DeepSeek's own chart where Flash scored 77.0 vs 74.0 on the same agent benchmark.
Measure how much of your usage limit resuming a long session costs
A developer tested resuming long sessions in Claude Code with Opus 5.5 and in Codex with GPT-6.1 Sol, both on medium effort, and watched the usage meters. Resuming a long Claude Code session took a big chunk of the 5-hour limit, while codex resume did not show the same jump.
Fix generic, too-fast motion graphics in agent-made launch videos
When Opus 5.5 is told to make a launch video dynamic, the motion often looks generic and too fast. The fix he shares is easing: soft entrances, shorter accelerating exits and no bouncing text, written up as a reference your agent can follow.