v26.4.1

Summary

• Fixed overly-aggressive removal of solver step caches. (#5458)

Full Changelog: v26.4.0...v26.4.1

v26.4.0

What's Changed

• Add zizmor config to ignore secrets-outside-env findings by @BradyPlanden in #5427
• Single model for experiment by @martinjrobins in #5422
• refactor: split Simulation into BaseSimulation and Simulation by @BradyPlanden in #5430
• Refactor casadi conversion by @MarcBerliner in #5436
• Adds frequency-domain EIS simulation support by @BradyPlanden in #5433
• Add ahead-of-time casadi compilation by @MarcBerliner in #5448
• Fix experiment initial guess regression by @MarcBerliner in #5452
• Fix termination hashes by @MarcBerliner in #5453
• Fix DomainError for hysteresis/MSMR OCP with particle size distribution and thermal by @rtimms in #5451
• Retry CasadiAlgebraicSolver if it terminates early due to step_tol by @MarcBerliner in #5457
• Adds memory leakage guard CI by @BradyPlanden in #5456

Full Changelog: v26.3.1...v26.4.0

v26.3.1

Bug fixes

• Fixed load_custom_model raising ImportError when the saved base class lives in a package not installed in the loading environment. The loader now falls back to pybamm.BaseModel with a warning. (#5441)
• Fixed serialisation bug in 2D finite volume discretisation. (#5434)

v26.3.0

What's Changed

• Lists of input parameters in initial conditions by @pipliggins in #5311
• Switch to npt.assert_allclose in unit tests by @pipliggins in #5362
• Fix ReadTheDocs builds by @BradyPlanden in #5363
• Use winget instead of chocolatey for graphviz on Windows by @BradyPlanden in #5365
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5366
• Build(deps): bump the actions group with 2 updates by @dependabot[bot] in #5367
• Add informative error message to simulation by @pipliggins in #5226
• Migrate dev and docs dependencies to dependency-groups by @AlessioBugetti in #5368
• test: refactor shared 2D mesh helper into pytest fixture by @swastim01 in #5342
• Improve numerical stability of exchange current density and OCPs by @MarcBerliner in #5371
• Support Python 3.14, drop JAX on macOS Intel by @BradyPlanden in #5374
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5378
• Build(deps): bump the actions group across 1 directory with 3 updates by @dependabot[bot] in #5377
• Fix file handle leaks in COMSOL comparison scripts by @taovinci0 in #5379
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5382
• Build(deps): bump astral-sh/setup-uv from 7.2.0 to 7.3.0 in the actions group by @dependabot[bot] in #5383
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5388
• perf: precalculate state mapper for mapping between experimental steps by @martinjrobins in #5380
• Remove mass matrix inverse and dense matrix temporaries by @MarcBerliner in #5391
• add roundtrip serialization tests by @valentinsulzer in #5394
• Build(deps): bump docker/build-push-action from 6.18.0 to 6.19.2 in the actions group by @dependabot[bot] in #5392
• Ensure bit-exact serialization roundtrips on parameters and simulations by @MarcBerliner in #5396
• Add debug logger to IDAKLUSolver by @MarcBerliner in #5395
• fix shape bug by @aabills in #5387
• Fix domain concat issue by @aabills in #5399
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5403
• Fix MSMR exchange current density regression by @MarcBerliner in #5404
• Hermite knot reduction by @MarcBerliner in #5390
• Add DiffSL export functionality by @martinjrobins in #5370
• fingerprint and cache esoh by @aabills in #5408
• Model to json by @rtimms in #5389
• Fix to_source() to preserve Interpolant data arrays by @rtimms in #5393
• Allow out-of-bounds initialisation by @Daniel-Nicolae23 in #5386
• Build(deps): bump the actions group across 1 directory with 3 updates by @dependabot[bot] in #5412
• perf: replace all_inputs_casadi with all_inputs_stacked by @MarcBerliner in #5413
• Preserve custom variables and events in built-in model to_config by @rtimms in #5411
• Fix psd 2 phases by @Ombrini in #5415
• Fix initial conditions not updating when inputs change at same SOC by @rtimms in #5418
• Fix Arcsinh2 in evaluate_python and JAX paths by @rtimms in #5420
• Build(deps): bump the actions group with 4 updates by @dependabot[bot] in #5416
• fix lychee by @BradyPlanden in #5423

New Contributors

• @taovinci0 made their first contribution in #5379
• @Ombrini made their first contribution in #5415

Full Changelog: v25.12.0...v26.3.0

v25.12.2

What's Changed

• Adds experimental CompositeSolver that retries solvers until one succeeds and updated the ESOH solvers to use a composite algebraic solver by @MarcBerliner in (#5357)

v25.12.1

What's Changed

• ParameterSubstitutor bugfixes by @BradyPlanden in #5352
• Improve composite eSOH by @rtimms in #5347

Full Changelog: v25.12.0...v25.12.1

v25.12.0

What's Changed

• fix 2d concat bug by @aabills in #5310
• Restructure idaklu jax tests by @pipliggins in #5315
• Fix non-deterministic CI by @MarcBerliner in #5316
• #5299 add inverse linear kinetics by @rtimms in #5303
• Observe custom variables after solving + faster simulation build time by @MarcBerliner in #5308
• fix idaklu jax test issue by @aabills in #5319
• [Fix] Handle missing geometry keys in latexify for lithium plating mo… by @swastim01 in #5245
• fix np trapz bug by @valentinsulzer in #5324
• use zlib to make serialization smaller by @aabills in #5323
• Build(deps): bump the actions group across 1 directory with 12 updates by @dependabot[bot] in #5322
• Fix benchmarks by @pipliggins in #5318
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5195
• Fix a race in serialisation test_save_load_model test by @agriyakhetarpal in #5325
• Adds Python 3.13 by @BradyPlanden in #5330
• Coupled variable serialization by @valentinsulzer in #5326
• copyright should only include the year of creation by @Saransh-cpp in #5332
• Fix coupled variable by @aabills in #5334
• Fix bug with fixed_input_parameters missing input params in symbols by @MarcBerliner in #5321
• Removes automatic addition of constants to ParameterValue object by @BradyPlanden in #5336
• add tensors and basic operators by @aabills in #5335
• Add Solution.yp getter by @MarcBerliner in #5341
• Restructures ParameterValues class by @BradyPlanden in #5339
• SciPy 1.17.0 FutureWarning for explicit types by @BradyPlanden in #5344
• asymmetric stress-driven LAM by @rtimms in #5343
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5345
• broadcast to edges 2d by @aabills in #5340
• Build(deps): bump astral-sh/setup-uv from 7.1.6 to 7.2.0 in the actions group by @dependabot[bot] in #5346
• BasicDFN2D with variable porosity and active fractions in x and z directions by @DrSOKane in #5266
• Volume fractions and porosity that vary in y and z by @DrSOKane in #5214
• Cherry pick composite esoh fixes by @rtimms in #5349

Full Changelog: https://github.com/pybamm-team/PyBaMM/blob/main/CHANGELOG.md#v25120---2026-01-15

Breaking changes

• Deprecates check_already_exists argument for ParameterValues.update(). This removes the secondary checking for explicit keys in the ParameterValues object. If a key is not found, it will be added. Note, this includes typos in parameter names. This changes update to have update-insert functionality whereas previously it required the check_already_exists flag to be False. This also allows for direct dictionary update-insert through parameter_values["key"] = "value". (#5339)
• Removes default constants added to ParameterValues on construction. Only breaking if you rely on this functionality in custom models, parameters, etc. (#5336)

v25.10.2

What's Changed

Bugfix serialising InputParameter's. (#5289)
Bugfix BaseModels's initial_conditions_from scale evaluation (#5285)
Bugfix with bulk ocp lithiation (#5280)

Full Changelog: v25.10.1...v25.10.2

v25.10.1

What's Changed

• Sync develop with main by @BradyPlanden in #5252
• fix wsl links by @valentinsulzer in #5251
• chore: modernise uv usage in CI + fix cache by @Saransh-cpp in #5249
• Add docstrings to FuzzyDict methods by @swastim01 in #5242
• fix: Fixing non-deterministic CI issues by @Rishab87 in #5255
• Build(deps): bump the actions group with 2 updates by @dependabot[bot] in #5259
• Fix bug with initial conditions that violate events by @MarcBerliner in #5260
• Fix/discussion autoresponder 5186 by @swastim01 in #5261
• update to pytest 9.0, remove pytest-subtests by @valentinsulzer in #5271
• Set initial conditions from y slice by @rtimms in #5257
• Plot voltage components bugfix by @Daniel-Nicolae23 in #5270
• Composite electrode bug-fix for swelling submodel by @BradyPlanden in #5272

Full Changelog: https://github.com/pybamm-team/PyBaMM/blob/develop/CHANGELOG.md#v25100---2025-10-29

v25.10.0

What's Changed

• Build(deps): bump the actions group with 2 updates by @dependabot[bot] in #5148
• Sync v25.8.0 with develop by @brosaplanella in #5149
• Fixed non-deterministic plotting CI issues by @Rishab87 in #5150
• 2D by @aabills in #5106
• Generalise initial state setting by @NicolaCourtier in #5129
• Attempt to Patch few non-deterministic CI issues. by @Rishab87 in #5156
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5147
• Build(deps): bump the actions group with 6 updates by @dependabot[bot] in #5157
• composite esoh by @aabills in #5160
• Total surface area to volume by @rtimms in #5165
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5166
• Build(deps): bump github/codeql-action from 3.29.8 to 3.29.10 in the actions group by @dependabot[bot] in #5167
• Added load_mesh_from_file function to support external 3D meshes. by @Rishab87 in #5162
• [GSoC 2025] Saving and Loading Custom Models by @medha-14 in #5056
• Fix drive cycle duration bug by @MarcBerliner in #5153
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5172
• Build(deps): bump the actions group with 3 updates by @dependabot[bot] in #5173
• fix 2d inner product by @aabills in #5175
• constant extrapolation in 2d by @aabills in #5178
• fix calculation of bulk ocp in hysteresis models by @rtimms in #5169
• Composite esoh half cell by @aabills in #5179
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5182
• Added an option for multiple initial conditions in IDAKLU solver by @Rishab87 in #4981
• chore: update pre-commit hooks by @pre-commit-ci[bot] in #5187
• Use T_init in initial_state by @rtimms in #5189
• Hysteresis ESOH by @aabills in #5163
• Build(deps): bump the actions group across 1 directory with 5 updates by @dependabot[bot] in #5188
• Update pybammsolvers to v0.2.0 by @MarcBerliner in #5199
• 1D+ sensitivities error with IDAKLU output_variables by @pipliggins in #5118
• Make time-based heaviside and modulo inputs explicit t_eval points with IDAKLUSolver by @MarcBerliner in #4994
• Add options to terminate IDAKLUSolver early when there's little progress by @MarcBerliner in #5201
• Computing Bruggeman coefficient from BPX porosity instead of hardcoding by @r0hansaxena in #5196
• Unpin numpy, bump pybammsolvers by @MarcBerliner in #5204
• Fix bug with out-of-bounds discontinuities in time by @MarcBerliner in #5205
• Fix doc links (make lychee happy) by @DavidMStraub in #5208
• Removes the default solver change warning by @BradyPlanden in #5209
• Added warning about installation through conda to docs and suggested installation via pip by @r0hansaxena in #5206
• [CI] Change MacOS runner from macos-13 to macos-15-intel by @DavidMStraub in #5213
• Remove deprecated JAX funtions by @DavidMStraub in #5203
• Build(deps): bump the actions group across 1 directory with 3 updates by @dependabot[bot] in #5216
• feat(EvaluateAt): add support for children evaluated at edges by @martinjrobins in #5190
• Build(deps): bump the actions group with 3 updates by @dependabot[bot] in #5220
• Allow sim to be pickled with output variables by @pipliggins in #5225
• Plot voltage components for composite electrodes by @Daniel-Nicolae23 in #5229
• Change fundamental SEI variable from thickness to concentration: attempt 2 by @DrSOKane in #4869
• #5198 update definition of hysteresis decay rate by @rtimms in #5217
• Serialise refactor by @aabills in #5235
• IDAKLU options property, fixes pickling issue with getstate by @BradyPlanden in #5234
• Serialise geometry varpts etc by @aabills in #5236
• [GSoC 2025] Serialising Parameter Sets by @medha-14 in #5177
• Update broken link by @valentinsulzer in #5246
• Build(deps): bump the actions group across 1 directory with 4 updates by @dependabot[bot] in #5243
• Set zip(..., strict=True) in key solver/expression tree files for len… by @swastim01 in #5241
• Fix: correct temperature initialisation in lumped and x_full thermal … by @swastim01 in #5248
• Enable contact overpotential display by @Jhah2025 in #5247
• Serialization refactor by @aabills in #5244
• Release v25.10.0 by @BradyPlanden in #5250

New Contributors

• @r0hansaxena made their first contribution in #5196
• @Daniel-Nicolae23 made their first contribution in #5229
• @swastim01 made their first contribution in #5241
• @Jhah2025 made their first contribution in #5247

Full Changelog: v25.8.0...v25.10.0