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

v25.8.0

Features

• Added plot_3d_cross_section & plot_3d_heatmap functions to support plotting for 3D thermal simulations. (#5130)
• Added a Basic3DThermalSPM with two way coupling. (#5112)
• Enables the passing of inputs throughout set_initial_soc. (#5122)
• Adds on_failure option to BaseSolver with options for "warn", "ignore", and "raise" to change behaviour on solver failure. Defaults to "raise" to retain historic functionality. (#5105)
• Creates a boundary mesh size object that returns the distance from the center of the leftmost/rightmost control volume to the boundary of the domain (#5108)
• Introduced entry points for models, similar to parameter sets, and moved entry point handling to pybamm.dispatch.entry_points. There is now experimental support for loading third-party models outside of the PyBaMM framework via pybamm.Model("model_name"). This API is currently unstable until further notice and may be subject to change without warning. (#4490)
• Allow for overriding the spatial method's extrapolation and for using constant extrapolation of boundary values (#5107)
• Creates BaseProcessedVariable to enable object combination when adding solutions together (#5076)
• Added a Constant symbol for named constants. This is a subclass of Scalar and is used to represent named constants such as the gas constant. This avoids constants being simplified out when constructing expressions. (#5070)
• Generalise pybamm.DiscreteTimeSum to allow it to be embedded in other expressions (#5044)
• Adds all key-value pair to output_variables sensitivity dictionaries, accessible through solution[var].sensitivities['all']. Aligns shape with conventional solution sensitivities object. (#5067)
• Added a new BaseHysteresisOpenCircuitPotential class that sets variables for the lithiation and delithiation OCP and the hysteresis voltage (H = U_lith - U_delith). Allow the initial hysteresis state to be a function of position through the electrode. Allow the hysteresis decay rates of the Axen and Wycisk models to be a function of stoichiometry and temperature. Added a heat source term in each active material phase Q_hys = i_vol * (U - U_eq) where i_vol is the volumetric interfacial current density, U is the OCP (i.e. includes hysteresis), and U_eq is the "equilibrium OCP". Renamed the open-circuit potential models to be more descriptive. The options "Axen" and "Wycisk" are now "one-state hysteresis" and "one-state differential capacity hysteresis". The old option names still work but will raise a warning. (#4893)
• Add support for output_variables to pybamm.DiscreteTimeSum and pybamm.ExplicitTimeIntegral expressions. (#5071)
• Added 3D FEM and meshes supporting rectangular and cylindrical geometries (#5009)

Bug fixes

• Fix non-deterministic ShapeError in 3D FEM gradient method (#5143)
• Fixes negative electrode boundary values for half-cell voltage contributions. (#5139)
• Makes A_cc L_z * L_y * number of layers (#5138)
• Fixes TimeIntegral expression node summation when dependent on an input parameter. (#5119)
• Fixed a bug that ignored the default duration of drive cycles for CRate steps and a bug that overwrote custom period arguments for drive cycles. (#5090)
• Converts sensitivities to numpy objects, fixing bug in DiscreteTimeSum sensitivity calculation (#5037)
• Raises error if pybamm.Interpolant given 1D x values that are not strictly increasing (#5061)
• Fixes inconsistency of the returned shape of a pybamm.DiscreteTimeSum variable depending on output_variables being set or not. (#5098)
• Fixed a bug where simplifications cause heavisides to evaluate as booleans (#4893)
• Fixed a bug in the WyciskOpenCircuitPotential model where the differential capacity was not being evaluated correctly. (#4893)

Breaking changes

• Changed behavior of drive cycle steps in pybamm.Experiments to treat each time point as a discontinuity, consistent with how input interpolants work. This ensures more accurate simulation of drive cycles with rapid changes. (#5141)
• Removed the IREE code from the IDAKLU solver (#5080)
• Removed support for Python 3.9 (#5052)
• In OCP hysteresis models, users need to explicitly give the equilibrium, delithiation, and lithiation OCPs when using a hysteresis model. E.g., you must provide all three of "Negative electrode OCP [V]", "Negative electrode delithiation OCP [V]", and "Negative electrode lithiation OCP [V]". (#4893)

v25.6.0

Features

• Renamed MSMR parameters from symbols to written out names with units as a non-breaking change with a deprecation warning. (#5027)

Optimizations

• Update docs, examples and tests to use IDAKLUSolver. (#4996)
• Add a solver option to change on_extrapolation behavior to "error", "warn", or "ignore" on extrapolation events. (#4993)
• Improve reliability of CasadiAlgebraicSolver and added an option for the step_tol of the Newton iteration. (#4985)
• Speed up calculation of variable sensitivities in ProcessedVariable (#5000)

Bug fixes

• Fixed a bug in the QuickPlot which would return empty values for 1D variables at the beginning and end of a timespan. (#4991)
• Fixed a bug in the Exponential1DSubMesh where the mesh was not being created correctly for non-zero minimum values. (#4989)
• Fixed sensitivity calculation for pybamm.DiscreteTimeSum. (#5007)

Breaking changes

• Remove sensitivity functionality for Casadi and Scipy solvers, only pybamm.IDAKLU solver can calculate sensitivities. (#4975)

v25.4.2

Bug fixes

• Improve reliability of AlgebraicSolver and change ElectrodeSOHHalfCell solver to a Trust-Region method. (#4982)

v25.4.1

Bug fixes

• Remove a regularization term in the harmonic mean. (#4977)

Breaking changes

• Changed default solver to pybamm.IDAKLUSolver. (#4915)

v25.4.0

Features

• Revision of the hysteresis notebook to include the method implemented in the module axen_ocp. (#4880)
• Added axen_ocp module within submodel interface.open_circuit_potential to handle an OCP with hysteresis. (#4816)
• Creates a 'calc_esoh' property in battery models (#4825)
• Added 'get_summary_variables' to return dictionary of computed summary variables (#4824)
• Added support for particle size distributions combined with particle mechanics. (#4807)
• Added InputParameter support in PyBamm experiments (#4826)
• Added support for the "pchip" interpolator using the CasADI backend. (#4871)

Breaking changes

• Added skip_ok option to step to allow for steps to be skipped if they are infeasible at initial conditions. (#4839)
• Deprecated CrateTermination and renamed it to CRateTermination. (#4834)

Bug fixes

• Fixed a bug with observing the outputs of 2D FEM simulations. (#4912)
• Fixed a bug in simulating FEM models with the IDAKLUSolver. (#4879)
• Moved concentration inside x-averaged when calculating LLI due to LAM variables (#4858)
• Fixed a bug that caused the variable "Loss of lithium due to {domain} lithium plating"to have the domain "current collector" (should not have any domain at all) if the "x-average side reactions" option was set to "true". (#4844)
• Fixed interpolation bug in pybamm.QuickPlot with spatial variables. (#4841)

Optimizations

• Performance improvements to IDAKLUSolver initialization and processed variables. (#4878)
• Improved search to handle cases with shorter input strings and provide more relevant results. (#4735)

v25.1.1

Features

• Added Operators to current and voltage termination events. (#4770)

Bug fixes

• Fixed a bug which caused the ec-reaction limited SEI model to give
  incorrect results (#4774)

v25.1.0

Features

• Added a dt_min option to the (IDAKLUSolver). (#4736)
• Automatically add state variables of the model to the output variables if they are not already present (#4700)
• Enabled using SEI models with particle size distributions. (#4693)
• Added symbolic mesh which allows for using InputParameters for geometric parameters (#4665)
• Enhanced the search method to accept multiple search terms in the form of a string or a list. (#4650)
• Made composite electrode model compatible with particle size distribution (#4687)
• Added Symbol.post_order() method to return an iterable that steps through the tree in post-order fashion. (#4684)
• Porosity change now works for composite electrode (#4417)
• Added two more submodels (options) for the SEI: Lars von Kolzenberg (2020) model and Tunneling Limit model (#4394)

Breaking changes

• Updated BPX to v0.5.0 and made changes for the switch to Pydantic V2 (#4701)
• Summary variables now calculated only when called, accessed via a class in the same manner as other variables rather than a dictionary. (#4621)
• The conda distribution (pybamm) now installs all optional dependencies available on conda-forge. Use the new pybamm-base conda
  package to install PyBaMM with only the required dependencies. (conda-forge/pybamm-feedstock#70)
• Separated extrapolation options for pybamm.BoundaryValue and pybamm.BoundaryGradient, and updated the default to be "linear" for the value and "quadratic" for the gradient. (#4614)
• Double-layer SEI models have been removed (with the corresponding parameters). All models assume now a single SEI layer. (#4470)
• Moved the IDAKLU solver to a standalone pybammsolvers package. This will
  make PyBaMM a pure Python package and make installing and using the solver
  easier. (#4487)
• Wycisk OCP model now requires an parameter to set the initial condition. (#4374)

Bug fixes

• Fixed bug when using stoichiometry-dependent diffusivity with the DFN model with a particle size distribution. (#4726)
• Remove internal use of deprecated set_parameters function in the Simulation class which caused warnings. (#4638)
• Provide default value for Symbol.mesh attribute to avoid errors when adding variables after discretisation. (#4644)