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)