What geometry kernel does SolidCraft use? truck today, SolidCore under evaluation
Short answer (October 2026): SolidCraft v0.18.2 does its solid modelling through its own kernel layer, solidcraft-kernel, which is built on the open-source Rust truck crates. On 21 October 2026 (UTC) the maintainers paused new kernel work while they evaluate a different kernel: SolidCore, a Rust port of NVIDIA's SMLib B-rep library. SolidCore is not ready yet. Its own README says about a third has been ported and "nothing is usable end to end yet". No decision has been announced, and the app you download today still runs on the truck-based kernel.
What a geometry kernel does
Every solid-modelling CAD program sits on a geometry kernel. The kernel stores a part as a boundary representation (B-rep): faces, edges and vertices tied to exact curves and surfaces. It also runs the hard operations: booleans, fillets, chamfers, shells, offsets, sweeps and lofts, and STEP import and export. The triangles you see on screen are only a mesh made from that exact geometry for display. The official SolidCore page explains it the same way.
That is why kernel quality shows up directly as user experience. When a fillet or shell "operation failed", the kernel is often the layer that gave up. Several of the newest issues on SolidCraft's tracker carry titles like "FILLET: operation failed", "SHELL: operation failed" and "EXTRUDE: operation failed" (21 October 2026).
What SolidCraft uses today: a truck-based kernel
- SolidCraft's kernel crate describes itself as the "SolidCraft B-rep kernel boundary: solids, extrude/revolve/booleans/fillets, tessellation, measures and STEP, behind our own API (implemented with truck)". It depends on
truck-modeling,truck-shapeops,truck-meshalgo,truck-stepioandtruck-topology. - truck is an open-source Rust CAD kernel from RICOS (Apache-2.0, developed since 2020). SolidCraft ships a modified copy of
truck-shapeops0.4.0 and lists the changes in its NOTICE file. - SolidCraft adds its own layers on top. Its project rules say "the sketch solver and the blend operations are our own". Every call into truck goes through a guard that turns a kernel panic into an error instead of a crash.
- Design files store the parametric timeline and, since 0.17, a compressed copy of the evaluated model, which makes reopening faster. The documented body format ("Native B-rep, schema 3") "has no modelling-backend dependency". The same document notes that some intersection curves "a different kernel must trace … again".
What changed on 20–21 October 2026
In an announcement posted at 03:11 UTC on 21 October (21:11 MDT on 20 October), the maintainers wrote that they are "evaluating a new geometry kernel for SolidCraft: solidcore, a safe, deterministic, wasm-friendly Rust B-rep kernel". Until a decision is made:
- They ask people not to open new issues, pull requests or discussions about kernel work: booleans, fillets, chamfers, shell, offsets, sweeps and lofts, threads and holes, STEP/IGES import and export, tessellation, or anything that changes
crates/kernel/. New ones get akernel-pausedlabel and an answer. - Open kernel pull requests were set to draft. Nothing was deleted, and the test cases people found "are going into the new kernel's regression suite".
- Everything outside the kernel carries on: UI, sketching, drawings, assemblies, rendering, docs, translations, tests and CI.
- Crashes and data loss are still welcome as issues and come first.
Tracking issue: #3992.
What SolidCore is
| SolidCore (as of 2026-10-21) | |
|---|---|
| What | A Rust port of SMLib, the B-rep kernel in NVIDIA's open-source USD BRep library (C++/Python, Apache-2.0) |
| Licence | Apache-2.0; the official page notes it is "not affiliated with or endorsed by NVIDIA" |
| Scope | NURBS maths, curves and surfaces, B-rep topology, intersections, booleans, fillets and chamfers, offset and shell, sweeps and skins, primitives, healing, mass properties. Upstream's OCCT translators, USD/Hydra integration and Python bindings are out of scope |
| Goals | No unsafe, no panics on bad input, deterministic results, no global state, builds for WebAssembly, and numerical agreement with the C++ original to 1e-9 (relative) with identical topology, checked unit by unit with a Rust-vs-C++ "difftest" |
| Status | "About a third ported and verified against the C++: the math, NURBS and curve layers, with surfaces and topology under way." "Nothing is usable end to end yet (no primitives, booleans or fillets)." |
| Progress | A public dashboard lists every unit's port status and test results |
The goals explain the appeal. A kernel that never panics, gives the same result every time and compiles to WebAssembly suits an app that also runs in the browser and is driven by AI agents.
What this means if you use SolidCraft
- Nothing changes in the app today. v0.18.2, the current release, models with the truck-based kernel, and so does the web app.
- Kernel fixes are on hold for now. Kernel pull requests are in draft and new kernel work is paused, so don't expect boolean or fillet fixes to land in the current kernel during the evaluation. This is our reading of the announcement, not a promise either way.
- Report crashes and lost work. The maintainers still put them first.
- Your files. The project has not said how designs will move if the kernel changes. The timeline is stored as commands and the cached body format is documented as backend-independent, but there is no official compatibility statement yet. Keep STEP exports of important parts, which is good practice anyway.
How this compares with other CAD programs
| Program | Kernel |
|---|---|
| SolidCraft 0.18.2 | Own kernel layer on the truck Rust crates (Apache-2.0); SolidCore under evaluation |
| FreeCAD | Open CASCADE Technology (OCCT), a long-standing C++ kernel (LGPL-2.1) |
| Many commercial CAD programs | Licensed commercial kernels such as Siemens Parasolid |
Writing a production-grade B-rep kernel is famously hard. At SolidCraft's Show HN launch a commenter pointed out the truck dependency and wrote that "creating a b-rep kernel is a phenomenal amount of work". More on the two open-source programs in SolidCraft vs FreeCAD.
Quick answers
Is SolidCraft switching to SolidCore? It is being evaluated. No decision has been announced (21 October 2026).
Is SolidCraft development paused? Only kernel work. The UI, sketching, assemblies, drawings, docs and translations continue.
Can I use SolidCore today? Not as a modelling kernel. It has no primitives, booleans or fillets yet.
Does SolidCraft use OpenCASCADE? No. The project's rules forbid reading or linking GPL/LGPL CAD code such as OpenCASCADE and FreeCAD. FreeCAD is only run as a separate program to compute reference values for tests.
Sources (checked 2026-10-21)
- Announcement: "Kernel work is paused while we evaluate a new geometry kernel", tangency-labs/solidcraft discussion #3993, and tracking issue #3992 — https://github.com/tangency-labs/solidcraft/discussions/3993
crates/kernel/Cargo.toml,NOTICE,AGENTS.md,docs/native-brep.md— https://github.com/tangency-labs/solidcraft- SolidCore README and progress site — https://github.com/tangency-labs/solidcore · https://tangency-labs.github.io/solidcore/
- Official SolidCore page — https://solidcraft.io/solidcore/
- NVIDIA USD BRep — https://github.com/NVIDIA-Omniverse/usd-brep
- truck — https://github.com/ricosjp/truck
- FreeCAD and OpenCASCADE — https://wiki.freecad.org/OpenCASCADE
- Parasolid — https://plm.sw.siemens.com/en-US/plm-components/parasolid/
- Show HN thread — https://news.ycombinator.com/item?id=50064840
More articles: SolidCraft blog · Not affiliated with SolidCraft or Tangency Labs (about this site).