[Users] The Thirty-First Release of the Einstein Toolkit

[Steven Brandt]

Release Announcement

Click here to read the announcement in HTML (with hyperlinks):
https://einsteintoolkit.org/about/releases/ET_2026_05_announcement.html

We are pleased to announce the thirty-first release (code name
"Hypatia") of the Einstein Toolkit, an open-source, community-developed
software infrastructure for relativistic astrophysics. The major changes
in this release include:

New thorns in this release:

  * Cottonmouth (CottonmouthBSSNOK4m, CottonmouthZ4c4m,
    CottonmouthGaugeWaveID, CottonmouthLinearWaveID) -- A new suite of
    GPU-accelerated spacetime evolution thorns for CarpetX, generated
    using the Einstein Engine code generator. CottonmouthBSSNOK4m and
    CottonmouthZ4c4m implement the BSSNOK and Z4c formulations of
    Einstein's equations with 4th-order stencils and matter support;
    CottonmouthGaugeWaveID and CottonmouthLinearWaveID provide
    corresponding test initial data.
  * CanudaX (CanudaX_BSSNMoL, CanudaX_NPScalars, CanudaX_ExactID) -- A
    new GPU-accelerated BSSN spacetime evolution suite for CarpetX,
    based on the Canuda library. Includes a BSSN evolution thorn,
    Newman-Penrose scalar Psi4 extraction, and exact initial data
    (Kerr, Teukolsky waves, Apples-with-Apples test cases).
  * TwoPuncturesX -- A new thorn providing a C++ interface to
    TwoPunctures binary black hole initial data, for use with the
    CarpetX driver.
  * ET_BHaHAHA --  A new thorn providing an Einstein Toolkit interface
    to BHaHAHA, the BlackHoles at Home Apparent Horizon Algorithm. It
    finds and tracks apparent horizons in numerical relativity
    simulations by interpolating ADMBase metric data to the spherical
    grids used by the BHaHAHA library, running the
    hyperbolic-relaxation horizon finder, and writing
    AHFinderDirect-style diagnostics.

Along with a new gallery example:
  * Black hole-neutron star merger: simulation of a black hole-neutron
    star merger using a simple equation of state and parameters
    targeted to match GW230529

Updated thorns and components:

  * CarpetX -- Added support for integer and complex grid array and
    scalar types; custom OpenMP reductions for NVIDIA HPC SDK compiler
    compatibility; named OpenMP critical sections; pinned Particles in
    interpolation.
  * GRHayL -- Added Noble2D con2prim for tabulated equations of state;
    generalized and cleaned con2prim backup strategy; new tabulated
    EOS reader; Doxygen documentation added.
  * GRHayLHD/GRHayLHDX -- Updated to use new tabulated EOS reader and
    new GRHayL API; fixed schedule to correctly use volume integrals
    group.
  * TOVola -- Bug fixes for Lagrange interpolation stability;
    regression tests made surface-aware; updated for new GRHayL API.
  * AHFinderDirect -- Fixed regex patterns in param.ccl for improved
    portability.
  * TwoPunctures -- Refactored to C++ with namespace isolation,
    enabling the new TwoPuncturesX thorn; added W-type precollapsed
    lapse option.
  * NewRadX -- Added support for CapyrX multipatch grids.
  * QuasiLocalMeasures -- Corrected sign in ADM linear momentum
    calculation.
  * SummationByParts -- Fixed duplicated switch construction and
    4th-order second derivative operator scheduling.
  * CCE_Export -- Added configurable array size parameter; minor
    documentation and portability fixes.
  * POWER -- Fixed detection of smallest timestep across radii;
    cleaned up output formatting.
  * Llama -- Fixed inconsistent volume calculation.
  * LeanBSSNMoL -- Removed explicit Cray pointer variable declarations
    for improved portability.
  * SphericalSurface -- Scheduling fix to ensure Set runs after Setup.
  * Kuibit -- Bumped to 1.6.1.

Updated external libraries:

  * AMReX -- Updated to version 25.11; added configurable CUDA
    architecture selection.
  * ADIOS2 -- Added missing stdint.h include for compatibility with
    GCC 15; improved MPI library handling.
  * Boost -- Added new external library thorn for Boost 1.84.0.
  * GSL -- Updated to GSL 2.8.
  * HDF5 -- Improved system library path detection.
  * PETSc -- Updated to PETSc 3.23.4.
  * Silo -- Build fix: disabled config-site directory reading.

In addition, bug fixes accumulated since the previous release have been
included, as well as stability and optimization improvements through
Simfactory.

The Einstein Toolkit is a collection of software components and tools
for simulating and analyzing general relativistic astrophysical systems.
It builds on numerous software efforts in the numerical relativity
community, including codes to compute initial data parameters, the
spacetime evolution codes Baikal, lean_public, McLachlan, CanudaX, and
Cottonmouth, analysis codes to compute horizon characteristics and
gravitational waves, and the relativistic (magneto)hydrodynamics codes
GRHayLHD, GRHayLHDX, GRHydro, and IllinoisGRMHD. Data analysis and
post-processing are handled by the kuibit library. The Einstein Toolkit
also contains a 1D self-force code. The toolkit supports two AMR
drivers: the established Carpet infrastructure, and the newer CarpetX
infrastructure built on the AMReX framework, which adds support for GPU
acceleration and block-structured adaptive mesh refinement on modern
supercomputing architectures. For parts of the toolkit, the Cactus
Framework is used as the underlying computational infrastructure,
providing large-scale parallelization, general computational components,
and a model for collaborative, portable code development.

The Einstein Toolkit uses a distributed software model. Its different
modules are developed, distributed, and supported either by the core
team of Einstein Toolkit Maintainers or by individual groups. Where
modules are provided by external groups, the Einstein Toolkit
Maintainers ensure quality control for modules included in the toolkit
and help coordinate support. The Einstein Toolkit Maintainers currently
involve staff and faculty from five different institutions and host
weekly meetings that are open to anyone.

Guiding principles for the design and implementation of the toolkit
include: open, community-driven software development; well thought-out
and stable interfaces; separation of physics software from computational
science infrastructure; provision of complete working production code;
training and education for a new generation of researchers.

For more information about using or contributing to the Einstein
Toolkit, or to join the Einstein Toolkit Consortium, please visit our
web pages at http://einsteintoolkit.org, or contact the users mailing
list users at einsteintoolkit.org.

The Einstein Toolkit is primarily supported by NSF 2411068 (E=mc2:
Enabling Multimessenger astrophysics through Community-driven
Cyberinfrastructure) and NSF
2004157/2004044/2004311/2004879/2003893/2114582/2227105 (Enabling
fundamental research in the era of multi-messenger astrophysics).

The Einstein Toolkit contains about 400 regression test cases. On a
large portion of the tested machines, almost all of these tests pass,
using both MPI and OpenMP parallelization.

Contributors

Among the many contributors to the Einstein Toolkit and to this release
in particular, important contributions to new and existing components
were made by the following authors:

  * Benjamin Meyers
  * Beyhan Karakas
  * Bruno Giacomazzo
  * Cheng-Hsin Cheng
  * Chloe B. Richards
  * David Boyer
  * Erik Schnetter
  * Gabriele Bozzola
  * Jordan Nicoules
  * Leonardo Werneck
  * Liwei Ji
  * Lucas Timotheo Sanches
  * Marco Brito
  * Maxwell Rizzo
  * Max Morris
  * Peter Diener
  * Rahime Matur
  * Roland Haas
  * Samuel Cupp
  * Samuel Tootle
  * Steven R. Brandt
  * Zachariah Etienne

How to upgrade from Martin D. Kruskal Release (ET_2025_05)

To upgrade from the previous release, use GetComponents with the new
thornlist to check out the new version.

See the Download page (http://einsteintoolkit.org/download.html) on the
Einstein Toolkit website for download instructions.

The SelfForce-1D code uses a single git repository; thus, using

git pull; git checkout ET_2026_05

will update the code.

To install Kuibit, do the following:

pip install --user -U kuibit==1.6.1

Machine notes

Supported (tested) machines include:

  * Debian, Ubuntu, Fedora, Mint, OpenSUSE, Alma, and Rocky
    installations with dependencies installed as prescribed in the
    official installation instructions
  * Anvil
  * Deep Bayou
  * Delta
  * DIRAC/Cosma 8
  * Expanse
  * Frontera
  * Queen Bee 3 and 4
  * Sunrise
  * Supermike

Note for individual machines:

  * TACC machines: defs.local.ini needs to have `sourcebasedir =
    $WORK` and `basedir = $SCRATCH/simulations` configured for this
    machine. You need to determine $WORK and $SCRATCH by logging in to
    the machine.

All repositories participating in this release carry a branch ET_2026_05
marking this release. These release branches will be updated if severe
errors are found.

The "Hypatia" Release Team on behalf of the Einstein Toolkit Consortium
(2026-07-10)

  * Steven R. Brandt (release manager)
  * Beyhan Karakas (assistant release manager)
  * Roland Haas (assistant co-chair)
  * Bing-Jyun Tsao
  * Deborah Ferguson
  * Cheng-Hsin Cheng
  * Leonardo Werneck
  * Lucas Timotheo Sanches
  * Maxwell Rizzo
  * Noora Ghadiri
  * Peter Diener
  * Rahime Matur
  * Yuvraj Sharma

July 10, 2026