New features:

• Added jax.thread_guard, a context manager that detects when devices are used by multiple threads in multi-controller JAX.

Bug fixes:

• Fixed a workspace size calculation error for pivoted QR (magma_zgeqp3_gpu) in MAGMA 2.9.0 when using use_magma=True and pivoting=True. (#34145).

Deprecations:

• The flag jax_collectives_common_channel_id was removed.
• The jax_pmap_no_rank_reduction config state has been removed. The no-rank-reduction behavior is now the only supported behavior: a jax.pmapped function f sees inputs of the same rank as the input to jax.pmap(f). For example, if jax.pmap(f) receives shape (8, 128) on 8 devices, then f receives shape (1, 128).
• Setting the jax_pmap_shmap_merge config state is deprecated in JAX v0.9.0 and will be removed in JAX v0.10.0.
• jax.numpy.fix is deprecated, anticipating the deprecation of numpy.fix in NumPy v2.5.0. jax.numpy.trunc is a drop-in replacement.

Changes:

• jax.export now supports explicit sharding. This required a new export serialization format version that includes the NamedSharding, including the abstract mesh, and the partition spec. As part of this change we have added a restriction in the use of exported modules: when calling them the abstract mesh must match the one used at export time, including the axis names. Previously, only the number of the devices mattered.