---
title: "Blocks UI migration | Nutrient"
canonical_url: "https://www.nutrient.io/guides/web/migration-guides/2025-blocks-ui-migration/"
md_url: "https://www.nutrient.io/guides/web/migration-guides/2025-blocks-ui-migration.md"
last_updated: "2025-08-13T00:00:00.000Z"
description: "Comprehensive upgrade guide for Nutrient Web SDK covering version migrations, breaking changes, and new features."
---

This migration only affects customers who are using the private customization API via `NutrientViewer.Configuration#ui`. To continue using this, move your existing configuration inside the `_blocks` property of the `ui` configuration object. You’ll also see a warning in your console if you’re using the older API.

Earlier:

```js

NutrientViewer.load({
  ui: {
    // Your config earlier.
  },
});

```

Now:

```js

NutrientViewer.load({
  ui: {
    // your config earlier

    _blocks: {
      // Your config goes inside `_blocks` now.
    },
  },
});

```

---

## Related pages

- [Migrate to electronic signatures](/guides/web/migration-guides/migrating-to-electronic-signatures.md)
- [Aria Labels Migration Guide](/guides/web/migration-guides/aria-labels-migration-guide.md)
- [Baseline Ui Migration Guide](/guides/web/migration-guides/baseline-ui-migration-guide.md)