Sarah Ager
Optimizely
Jun 11, 2025
visibility 1550
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JavaScript SDK v6: Lightest, Most Efficient SDK Yet

Need a faster site and less frontend bloat? JavaScript SDK v6 is here —and it’s the lightest, smartest SDK we’ve ever released for Optimizely Feature Experimentation. 

🚀 What’s New in v6? 

  • Smaller Bundle Size: v6 slashes the bundle size down to as little as 22KB (gzipped) when configured for your needs. This means faster load times and a smoother experience for your users. 

  • Smarter Resource Management: No more manual deactivation in server-side rendering (SSR) environments. JavaScript SDK v6 manages resources more efficiently, simplifying your workflow. 

  • Advanced Decisioning Logic: Get ready for upcoming features like Contextual Bandits, async decision methods, and expanded compatibility with external datastores for sticky bucketing. 

⚠️ Before You Upgrade 

This is a major version update (v5 → v6) and includes breaking changes. 

If you rely on auto-importing the latest SDK version, now’s the time to double-check. You'll likely need to update your imports and integration logic to make the most of the improvements. 

Tip: Always pin SDK versions explicitly to avoid surprises when major updates roll out. 

🧠 Best Practices and Recommendations 

  • Avoid blindly importing packages using @latest. 

  • Review your dependencies regularly—especially SDKs that affect critical experiences. 

  • Check your SSR logic if migrating from v5—v6 simplifies it, but old patterns may conflict. 

✅ Upgrade Today! 

Ready to experience the benefits of JavaScript SDK v6? Upgrade now and enjoy a lighter, faster, and more efficient SDK for Optimizely Feature Experimentation. 

👉 Check out the JavaScript SDK upgrade guide for everything you need to make the switch. 

📚 Need Help? 

Our support docs walk you through the upgrade, step by step. Still stuck? Reach out to support or your account team. And don't forgeting to join the community Slack. 

Jun 11, 2025

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