Datadog's AI-Powered Test-Driven Migration Success

The 45-minute operation that nobody wanted to touch

Datadog's Stream Router was bleeding milliseconds. As the routing table grew, the most demanding operations ballooned to 45 minutes — executed across thousands of sequential round trips to a key-value store that was never designed to behave like a relational database. That's the kind of perf cliff where most teams start scheduling a rewrite, freeze new features, and quietly look for other jobs.

What Datadog actually did is more interesting than a rewrite. They used Claude and Cursor to accelerate a test-driven refactor of the existing codebase, kept production running on the old model while the new model landed in parallel, and shipped without a feature freeze.

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