Updating to latest 3D Gaussian Extensions and deprecating initial experimental version

[weegeekps]

Summary

We are updating Cesium JS to support the latest version of the glTF extensions for 3D Gaussian Splatting. Support for the extension version from initial release is now deprecated and will be removed with the November 2025 release of CesiumJS.

Deprecation Plan

While the 3D Gaussian splatting feature is currently experimental, we want to give people time to retile their content with the new tiler that will be released at the same time as these changes to CesiumJS.

September 2025 Release

Support for the version of the glTF extension, KHR_spz_gaussian_splats_compression, released in June 2025 is now deprecated, but users can still load 3D Tiles tilesets using this version of the extension.

The 3D Gaussian splatting tiler in ion has been updated and outputs 3D Tiles tilesets using the current version of the glTF extension specifications: KHR_gaussian_splatting and KHR_gaussian_splatting_compression_spz_2.

The 3D Gaussian splatting support within this release is still experimental and there may be changes again in the future, but we are hopeful that future changes will be less impactful.

We advise that during this time before the November 2025 release, you retile your data using the latest version of the tiler.

November 2025 Release

Support for the original KHR_spz_gaussian_splats_compression extension will be removed, and only 3D Tiles tilesets using the KHR_gaussian_splatting and KHR_gaussian_splatting_compression_spz_2 tilesets will be supported.

The why

Since the initial release of the 3D Gaussian Splatting for 3D Tiles support in CesiumJS, there have been significant updates to the glTF extensions that we need to implement. The changes include:

• Splitting the extension from a singular extension, KHR_spz_gaussian_splats_compression, to two extensions: KHR_gaussian_splatting and KHR_gaussian_splatting_compression_spz_2.
• Adding namespaces to the custom attribute semantics defined by the glTF extension.
• Handling the SPZ extension as a child of the base 3DGS extension.

[weegeekps]

cc: @shehzan10, @ggetz, @keyboardspecialist

[shehzan10]

@weegeekps Thanks for communicating this.

Lets make sure that when tilesets with the deprecated extensions are detected, we communicate sufficient warnings to educate users on the steps to be taken.

[weegeekps]

Lets make sure that when tilesets with the deprecated extensions are detected, we communicate sufficient warnings to educate users on the steps to be taken.

We will log a warning in the console explaining that the data needs to be retiled before November 2025.

[weegeekps]

I opened #12842 to track the removal of the KHR_spz_gaussian_splats_compression extension support in the 1.135 release slated for November.

[jo-chemla]

That's great news to see this PR upgrading from the original extension draft to the v2!

Does this mean that you deem the extensions (base and spz) is stable enough following community feedback and that it will probably be merged as-is - with only eventually a few minor upgrades - in the glTF repo? Thanks!

[ggetz]

@weegeekps Would you be able to answer this question? You're more in the know on this than I am 🙂 .

[weegeekps]

Oops, I actually meant to reply to this, but it got lost in the shuffle. Sorry, @jo-chemla!

To answer your question, there is one more set of changes incoming based on the recent feedback post-SIGGRAPH that I am currently working on with the plan of posting the updates this week. Those changes are largely around additional metadata that others have requested regarding kernel shapes, cut-offs, fall-off densities, and small adjustments to allow for quantization by other extensions.

I don't expect any of the changes that are incoming should impact what is currently in use. With the exception of expanding the datatypes for a few of the attribute accessors, the rest are changes to the renderingHints block.

[wula-lalala]

How can i use KHR_gaussian_splatting and KHR_gaussian_splatting_compression_spz_2 to convert a PLY file to GLB file