glTF 2.1

# glTF 2.1

glTF 2.1 is a focused, backwards-compatible revision of the core spec. It does not break existing glTF 2.0 content. Its goals are:

- Extend the format to support large-scale, complex, and production 3D workflows that are not well served today
- Lay a rigorous foundation — spatial primitives and multi-file composition — that extensions and future spec work can build on reliably

Every feature is being developed using a Design First process: explainers define purpose, scope, behavior, and inter-feature relationships before any schema or normative text is written.

## Core Features
The following features are confirmed for inclusion in the glTF 2.1 core. Each has a dedicated explainer linked below.

**Complex Scenes**
- *External Assets* - Standardized mechanism for a glTF file to reference external glTF files and assets as part of its scene graph, enabling multi-file scene composition
- *Bounding Volume Hierarchy* - Per-node bounding volume definitions using implicit shape types
- *Shapes* - Includes implicit geometric primitives (box, sphere, capsule, cylinder, and others) to core, enabling physics, collision, and procedural workflows without explicit mesh geometry
- *Packaging External Assets* - Allows a glTF file to act as a virtual package for a complex scene: embedded external assets resolve URIs through the host file's files array, enabling shared buffers, textures, and resources across nested glTF files without modifying original data
- *Unified File References* - A single array of file references for all future external content types referenced within a glTF file; ships as part of External Assets
- *Multiple Scene Deprecation* - Formally deprecates the multiple-scenes pattern; glTF files are expected to contain a single scene going forward

**Quality of Life improvements**
- *Promoted Extension Functionality* - Promotes the functionality of these specific extensions ratified in glTF 2.0 to required status in glTF 2.1:
[EXT_texture_webp](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Vendor/EXT_texture_webp)
[KHR_materials_emissive_strength](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_emissive_strength)
[KHR_mesh_quantization](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_mesh_quantization)
[KHR_node_visibility](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_node_visibility)
- *Thumbnails* - Embed standardized preview images directly in a glTF file for use in file browsers, asset managers, and pipelines without requiring a renderer
- *64-Bit Binary File Format* - Upgrades GLB chunk length fields from 32-bit to 64-bit, removing the ~4 GB per-chunk size ceiling
- *Non-Sequential Attributes* - Relaxes the requirement that indexed attribute semantics such as TEXCOORD_* and COLOR_* must start from zero and be consecutive, simplifying conversion workflows
- *Accessor Component Type Definitions* - Added commonly used type definitions for convenience of extension development
- *Unique IDs* - String identifiers scoped to a glTF file, providing stable, addressable identity for cross-file referencing and toolchain interoperability

## Status and Participation
The specification is under active development. Feature explainers are the current stable reference; schema and normative text to follow.

The glTF 2.1 specification progress will be openly available. Community feedback is encouraged. Organizations seeking a direct role in shaping the spec are welcome to [join the Khronos Group](https://www.khronos.org/members) and participate in the 3D Formats Working Group glTF 2.1 DTSG.

Start with the feature explainers referenced in the issue, then review how their scopes and relationships fit the proposed glTF 2.1 core revision. The issue is a broad design roadmap; a concrete implementation target and definition of done are not specified here.

Written by the indexing model from the issue text.