transformer_lens.model_bridge.compat module

Compatibility shims for transformers version differences.

These patches are applied lazily (only when missing) so they’re safe to call from multiple adapters — the first caller wins, subsequent calls are no-ops.

WARNING: patches here mutate classes from the installed transformers package in place. They are process-global and persist for the entire Python session — every model loaded afterward, including ones unrelated to the caller, sees the patched class. This is acceptable because the shims only add v4-era methods that v5 removed; they do not change v5 behavior. But it means a bug in a shim affects the whole session, not just the adapter that invoked it.

REMOVAL: drop the corresponding block (and its call sites) once the minimum supported transformers version provides the method natively, or once all remote-code models we support have been updated for v5. Track upstream status against transformers.cache_utils.DynamicCache — when from_legacy_cache, to_legacy_cache, and get_usable_length are restored or no longer needed, patch_dynamic_cache_v5 can be deleted outright.

transformer_lens.model_bridge.compat.patch_dynamic_cache_v5() → None

Backfill DynamicCache methods removed in transformers v5.

Remote-code models written for transformers v4 call from_legacy_cache, to_legacy_cache, and get_usable_length which were removed in v5. Call this from any adapter’s prepare_loading() that needs them.

Side effect: mutates transformers.cache_utils.DynamicCache for the whole process. See module docstring.