Python function bundles now include precompiled bytecode
2.8s to 1.3s. Vercel just cut Python cold starts in half with precompiled bytecode.
Why it matters
Vercel's bytecode precompilation is a meaningful infrastructure optimization for AI/ML workloads running on serverless. For teams deploying inference functions or data pipelines, 53% cold-start reduction directly impacts latency-sensitive applications and operational costs.
The key facts
11 to knowCold start time reduced from 2.8s to 1.3s (53% improvement)
Precompilation happens at build time, not runtime
Applies to both application code and dependencies
.pyc files bundled automatically
No code changes required from developers
Larger functions near bundle size limit see smaller gains
Cold start reduction: 2.8s → 1.3s (53% improvement for median-sized functions)
Feature: Automatic .pyc bytecode compilation at build time for application code and dependencies
No code changes required for developers
Functions near size limits see smaller gains due to bundle constraints
Published July 20, 2026
Go to the source
Vercel Blogvercel.com
Publisher excerpt: Vercel now compiles Python functions to bytecode at build time. In our benchmarks, cold starts for the median-sized function dropped from .2.8s to 1.3s When Python imports a module without cached bytecode, it parses and compiles the source before executing it. That compilation step adds startup…