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OpenAI's GPT-6.1 Sol hits 86.6% on COBOL migration test

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OpenAI's GPT-6.1 Sol hits 86.6% on COBOL migration test

3 Key Points

  1. What happened

    OpenAI said GPT-6.1 Sol scored 86.6% on its COBOL migration benchmark at a low reasoning setting, versus 5.4% for GPT-5.6 Sol, at 61% of that model's API cost; higher reasoning reached 97.9%.

  2. Why it matters

    A near-perfect score means AI can now largely automate the mechanical translation of legacy COBOL, but OpenAI still requires expert review and business-rule testing before production use, so the tool speeds the work without removing human oversight.

WHO IT HITSIT teams maintaining COBOL-based banking and ATM systems stand to gain a faster first-pass translation tool, though the body notes that production deployment still requires expert review and testing against business rules.

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Context & Analysis

OpenAI's announcement centers on two benchmarks it built to measure how well its models handle programming languages with sparse training resources. The first, MultiLangBench, asks models to build a SQLite-compatible database engine from scratch in 20 languages; there, GPT-6.1 Sol reached an average test pass rate of 87.4%, up from 26.8% for GPT-5.6 Sol, while COBOL remained the hardest language at 72.1%, up from 10.9%.

The second, the COBOL migration evaluation, tests whether a model can rewrite an existing COBOL program into another language while preserving behavior. Because COBOL is used in over 40% of online banking systems and 95% of ATM transactions, per OpenAI, the company set a strict bar: a migration counts as successful only if all outputs match byte-for-byte on a non-public test. The results show a sharp jump from GPT-5.6 Sol's 5.4% accuracy to GPT-6.1 Sol's 86.6% at low reasoning, with 97.9% at higher reasoning, nearing the benchmark's ceiling.

OpenAI frames the cost angle as well: GPT-6.1 Sol's API cost is 61% of GPT-5.6 Sol's. Even so, the company cautions that production use of AI-migrated code still requires expert review and testing against business rules and dependencies, suggesting the tool is positioned as an accelerator rather than a replacement for human verification.

FAQ
How does OpenAI grade the COBOL migration test?
The company uses a non-public test that requires observable outputs to match byte-for-byte, and a migration is judged successful only if all tests pass. Migration targets are C++, Java, Kotlin, Python, and Rust.
Why is byte-level accuracy so important for COBOL migration?
COBOL programs handle financial transactions and business records, and details like rounding rules are embedded in the code. A rewritten program that rounds differently can change monetary results even if it runs without errors.
What does OpenAI say is needed before using AI-migrated code in production?
OpenAI states that applying model-based migration to production software still requires expert review and testing against the system's business rules and dependencies.
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