pyvene: Causal Interventions for Neural Networks
pyvene is Stanford NLP's library for performing causal interventions on PyTorch models. It provides a declarative, dict-based framework for activation patching, causal tracing, and interchange intervention training - making intervention experiments reproducible and shareable.
GitHub: stanfordnlp/pyvene (840+ stars) Paper: pyvene: A Library for Understanding and Improving PyTorch Models via Interventions (NAACL 2024)
When to Use pyvene
Use pyvene when you need to:
Perform causal tracing (ROME-style localization) Run activation patching experiments Conduct interchange intervention training (IIT) Test causal hypotheses about model components Share/reproduce intervention experiments via HuggingFace Work with any PyTorch architecture (not just transformers)
Consider alternatives when:
You need exploratory activation analysis → Use TransformerLens You want to train/analyze SAEs → Use SAELens You need remote execution on massive models → Use nnsight You want lower-level control → Use nnsight Installation pip install pyvene
Standard import:
import pyvene as pv
Core Concepts IntervenableModel
The main class that wraps any PyTorch model with intervention capabilities:
import pyvene as pv from transformers import AutoModelForCausalLM, AutoTokenizer
Load base model
model = AutoModelForCausalLM.from_pretrained("gpt2") tokenizer = AutoTokenizer.from_pretrained("gpt2")
Define intervention configuration
config = pv.IntervenableConfig( representations=[ pv.RepresentationConfig( layer=8, component="block_output", intervention_type=pv.VanillaIntervention, ) ] )
Create intervenable model
intervenable = pv.IntervenableModel(config, model)
Intervention Types Type Description Use Case VanillaIntervention Swap activations between runs Activation patching AdditionIntervention Add activations to base run Steering, ablation SubtractionIntervention Subtract activations Ablation ZeroIntervention Zero out activations Component knockout RotatedSpaceIntervention DAS trainable intervention Causal discovery CollectIntervention Collect activations Probing, analysis Component Targets
Available components to intervene on
components = [ "block_input", # Input to transformer block "block_output", # Output of transformer block "mlp_input", # Input to MLP "mlp_output", # Output of MLP "mlp_activation", # MLP hidden activations "attention_input", # Input to attention "attention_output", # Output of attention "attention_value_output", # Attention value vectors "query_output", # Query vectors "key_output", # Key vectors "value_output", # Value vectors "head_attention_value_output", # Per-head values ]
Workflow 1: Causal Tracing (ROME-style)
Locate where factual associations are stored by corrupting inputs and restoring activations.
Step-by-Step import pyvene as pv from transformers import AutoModelForCausalLM, AutoTokenizer import torch
model = AutoModelForCausalLM.from_pretrained("gpt2-xl") tokenizer = AutoTokenizer.from_pretrained("gpt2-xl")
1. Define clean and corrupted inputs
clean_prompt = "The Space Needle is in downtown" corrupted_prompt = "The ##### ###### ## ## ########" # Noise
clean_tokens = tokenizer(clean_prompt, return_tensors="pt") corrupted_tokens = tokenizer(corrupted_prompt, return_tensors="pt")
2. Get clean activations (source)
with torch.no_grad(): clean_outputs = model(**clean_tokens, output_hidden_states=True) clean_states = clean_outputs.hidden_states
3. Define restoration intervention
def run_causal_trace(layer, position): """Restore clean activation at specific layer and position.""" config = pv.IntervenableConfig( representations=[ pv.RepresentationConfig( layer=layer, component="block_output", intervention_type=pv.VanillaIntervention, unit="pos", max_number_of_units=1, ) ] )
intervenable = pv.IntervenableModel(config, model)
# Run with intervention
_, patched_outputs = intervenable(
base=corrupted_tokens,
sources=[clean_tokens],
unit_locations={"sources->base": ([[[position]]], [[[position]]])},
output_original_output=True,
)
# Return probability of correct token
probs = torch.softmax(patched_outputs.logits[0, -1], dim=-1)
seattle_token = tokenizer.encode(" Seattle")[0]
return probs[seattle_token].item()
4. Sweep over layers and positions
n_layers = model.config.n_layer seq_len = clean_tokens["input_ids"].shape[1]
results = torch.zeros(n_layers, seq_len) for layer in range(n_layers): for pos in range(seq_len): results[layer, pos] = run_causal_trace(layer, pos)
5. Visualize (layer x position heatmap)
High values indicate causal importance
Checklist Prepare clean prompt with target factual association Create corrupted version (noise or counterfactual) Define intervention config for each (layer, position) Run patching sweep Identify causal hotspots in heatmap Workflow 2: Activation Patching for Circuit Analysis
Test which components are necessary for a specific behavior.
Step-by-Step import pyvene as pv from transformers import AutoModelForCausalLM, AutoTokenizer import torch
model = AutoModelForCausalLM.from_pretrained("gpt2") tokenizer = AutoTokenizer.from_pretrained("gpt2")
IOI task setup
clean_prompt = "When John and Mary went to the store, Mary gave a bottle to" corrupted_prompt = "When John and Mary went to the store, John gave a bottle to"
clean_tokens = tokenizer(clean_prompt, return_tensors="pt") corrupted_tokens = tokenizer(corrupted_prompt, return_tensors="pt")
john_token = tokenizer.encode(" John")[0] mary_token = tokenizer.encode(" Mary")[0]
def logit_diff(logits): """IO - S logit difference.""" return logits[0, -1, john_token] - logits[0, -1, mary_token]
Patch attention output at each layer
def patch_attention(layer): config = pv.IntervenableConfig( representations=[ pv.RepresentationConfig( layer=layer, component="attention_output", intervention_type=pv.VanillaIntervention, ) ] )
intervenable = pv.IntervenableModel(config, model)
_, patched_outputs = intervenable(
base=corrupted_tokens,
sources=[clean_tokens],
)
return logit_diff(patched_outputs.logits).item()
Find which layers matter
results = [] for layer in range(model.config.n_layer): diff = patch_attention(layer) results.append(diff) print(f"Layer {layer}: logit diff = {diff:.3f}")
Workflow 3: Interchange Intervention Training (IIT)
Train interventions to discover causal structure.
Step-by-Step import pyvene as pv from transformers import AutoModelForCausalLM import torch
model = AutoModelForCausalLM.from_pretrained("gpt2")
1. Define trainable intervention
config = pv.IntervenableConfig( representations=[ pv.RepresentationConfig( layer=6, component="block_output", intervention_type=pv.RotatedSpaceIntervention, # Trainable low_rank_dimension=64, # Learn 64-dim subspace ) ] )
intervenable = pv.IntervenableModel(config, model)
2. Set up training
optimizer = torch.optim.Adam( intervenable.get_trainable_parameters(), lr=1e-4 )
3. Training loop (simplified)
for base_input, source_input, target_output in dataloader: optimizer.zero_grad()
_, outputs = intervenable(
base=base_input,
sources=[source_input],
)
loss = criterion(outputs.logits, target_output)
loss.backward()
optimizer.step()
4. Analyze learned intervention
The rotation matrix reveals causal subspace
rotation = intervenable.interventions["layer.6.block_output"][0].rotate_layer
DAS (Distributed Alignment Search)
Low-rank rotation finds interpretable subspaces
config = pv.IntervenableConfig( representations=[ pv.RepresentationConfig( layer=8, component="block_output", intervention_type=pv.LowRankRotatedSpaceIntervention, low_rank_dimension=1, # Find 1D causal direction ) ] )
Workflow 4: Model Steering (Honest LLaMA)
Steer model behavior during generation.
import pyvene as pv from transformers import AutoModelForCausalLM, AutoTokenizer
model = AutoModelForCausalLM.from_pretrained("meta-llama/Llama-2-7b-hf") tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-2-7b-hf")
Load pre-trained steering intervention
intervenable = pv.IntervenableModel.load( "zhengxuanzenwu/intervenable_honest_llama2_chat_7B", model=model, )
Generate with steering
prompt = "Is the earth flat?" inputs = tokenizer(prompt, return_tensors="pt")
Intervention applied during generation
outputs = intervenable.generate( inputs, max_new_tokens=100, do_sample=False, )
print(tokenizer.decode(outputs[0]))
Saving and Sharing Interventions
Save locally
intervenable.save("./my_intervention")
Load from local
intervenable = pv.IntervenableModel.load( "./my_intervention", model=model, )
Share on HuggingFace
intervenable.save_intervention("username/my-intervention")
Load from HuggingFace
intervenable = pv.IntervenableModel.load( "username/my-intervention", model=model, )
Common Issues & Solutions Issue: Wrong intervention location
WRONG: Incorrect component name
config = pv.RepresentationConfig( component="mlp", # Not valid! )
RIGHT: Use exact component name
config = pv.RepresentationConfig( component="mlp_output", # Valid )
Issue: Dimension mismatch
Ensure source and base have compatible shapes
For position-specific interventions:
config = pv.RepresentationConfig( unit="pos", max_number_of_units=1, # Intervene on single position )
Specify locations explicitly
intervenable( base=base_tokens, sources=[source_tokens], unit_locations={"sources->base": ([[[5]]], [[[5]]])}, # Position 5 )
Issue: Memory with large models
Use gradient checkpointing
model.gradient_checkpointing_enable()
Or intervene on fewer components
config = pv.IntervenableConfig( representations=[ pv.RepresentationConfig( layer=8, # Single layer instead of all component="block_output", ) ] )
Issue: LoRA integration
pyvene v0.1.8+ supports LoRAs as interventions
config = pv.RepresentationConfig( intervention_type=pv.LoRAIntervention, low_rank_dimension=16, )
Key Classes Reference Class Purpose IntervenableModel Main wrapper for interventions IntervenableConfig Configuration container RepresentationConfig Single intervention specification VanillaIntervention Activation swapping RotatedSpaceIntervention Trainable DAS intervention CollectIntervention Activation collection Supported Models
pyvene works with any PyTorch model. Tested on:
GPT-2 (all sizes) LLaMA / LLaMA-2 Pythia Mistral / Mixtral OPT BLIP (vision-language) ESM (protein models) Mamba (state space) Reference Documentation
For detailed API documentation, tutorials, and advanced usage, see the references/ folder:
File Contents references/README.md Overview and quick start guide references/api.md Complete API reference for IntervenableModel, intervention types, configurations references/tutorials.md Step-by-step tutorials for causal tracing, activation patching, DAS External Resources Tutorials pyvene 101 Causal Tracing Tutorial IOI Circuit Replication DAS Introduction Papers Locating and Editing Factual Associations in GPT - Meng et al. (2022) Inference-Time Intervention - Li et al. (2023) Interpretability in the Wild - Wang et al. (2022) Official Documentation Official Docs API Reference Comparison with Other Tools Feature pyvene TransformerLens nnsight Declarative config Yes No No HuggingFace sharing Yes No No Trainable interventions Yes Limited Yes Any PyTorch model Yes Transformers only Yes Remote execution No No Yes (NDIF)