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Apr 7, 2025

4 Advanced Cross-Validation Techniques for Optimizing Large Language Models

Conor Bronsdon

Head of Developer Awareness

Conor Bronsdon

Head of Developer Awareness

Picture this: you're responsible for optimizing LLMs for making crucial decisions that affect thousands of users every day. How confident are you in their performance?

The truth is, traditional validation methods that work for regular machine learning models just don't cut it when dealing with generative AI.

This is where optimizing LLMs with cross-validation shines. It's not just about measuring performance—it's a comprehensive strategy to fine-tune your LLM for better generalization and reliability, helping your models perform consistently even in demanding enterprise-scale AI settings.

This article discusses four comprehensive cross-validation techniques with implementation codes to transform your approach to LLM optimization, helping your models perform consistently even in demanding enterprise settings.

We recently explored this topic on our Chain of Thought podcast, where industry experts shared practical insights and real-world implementation strategies.

What is Cross-Validation for LLMs?

Cross-validation is a fundamental technique in machine learning for assessing model performance. LLMs operate at a scale we've never seen before—models like GPTs and Claude contain hundreds of billions of parameters. This massive capacity creates a real risk of memorization instead of true learning.

With so many parameters, these models can easily overfit to their training data, making thorough validation absolutely necessary when optimizing LLMs with cross-validation to build high-quality models. Applying AI model validation best practices is critical. Adopting data-centric approaches can also help mitigate overfitting.

The stakes are particularly high with generative models compared to discriminative ones. A simple classification error might produce one wrong label, but an overfitted LLM can generate text that sounds completely plausible yet contains factual errors, also known as LLM hallucinations, across many different topics.

Distribution shifts are another critical vulnerability for LLMs. Unlike simpler models, language models must handle constantly evolving language patterns, topics, and cultural contexts. Optimizing LLMs with cross-validation helps identify how well a model manages these shifts before deployment.

Now that we understand why optimizing LLMs with cross-validation matters, let's explore practical implementation strategies. The next sections provide hands-on guidance for designing effective cross-validation frameworks and integrating them into your LLM performance optimization development pipeline.

Learn how to create powerful, reliable AI agents with our in-depth eBook.

LLM Cross-Validation Technique #1: Implementing K-Fold Cross-Validation for Optimizing LLMs

K-fold cross-validation helps ensure your LLM models work well on data they haven't seen before. Implementing it specifically for optimizing LLMs with cross-validation means addressing unique challenges related to data volume, computational needs, and model complexity.

Here's a practical approach that balances thoroughness with computational efficiency.

Creating good folds for LLM validation requires more strategic thinking than simple random splitting. For effective LLM validation, start by stratifying your folds based on prompt types, answer lengths, or domain categories.

This ensures each fold contains a representative mix of your diverse prompt-response pairs, preventing situations where performance varies wildly between folds due to ML data blindspots.

When working with fine-tuning datasets that include demographic information, ensure balanced representation across all folds to prevent biased evaluations. This is particularly important for applications where fairness across different user groups is essential.

Implement Computational Efficiency Tricks

Running full k-fold validation on large LLMs can be computationally expensive, but several techniques make it feasible. Parameter-efficient fine-tuning methods like LoRA or QLoRA dramatically reduce the computational load, cutting cross-validation overhead by up to 75% while maintaining 95% of full-parameter performance.

Also, use checkpointing strategically to optimize your validation approach. Instead of training from scratch for each fold, start from a common checkpoint and then fine-tune on each training fold. This significantly reduces total computation time while preserving the integrity of your validation.

In addition, consider using mixed precision training and appropriate batch size adjustments to maximize GPU usage. For large models, gradient accumulation lets you maintain effectively large batch sizes even on limited hardware, keeping your cross-validation runs efficient without sacrificing stability.

Here's a practical implementation of k-fold cross-validation for optimizing LLMs with cross-validation using Hugging Face Transformers:

from sklearn.model_selection import KFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import numpy as np

# Load model and tokenizer
model_name = "facebook/opt-350m"  # Use smaller model for cross validation
tokenizer = AutoTokenizer.from_pretrained(model_name)
dataset = load_your_dataset()  # Your dataset loading function

# Configure k-fold cross validation
k_folds = 5
kf = KFold(n_splits=k_folds, shuffle=True, random_state=42)

# Track metrics across folds
fold_results = []

Now, let's set up the training loop for each fold:

for fold, (train_idx, val_idx) in enumerate(kf.split(dataset)):
    print(f"Training fold {fold+1}/{k_folds}")
    
    # Split data
    train_dataset = dataset.select(train_idx)
    val_dataset = dataset.select(val_idx)
    
    # Initialize model from checkpoint (prevents memory issues)
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training with memory efficiency in mind
    training_args = TrainingArguments(
        output_dir=f"./results/fold-{fold}",
        evaluation_strategy="steps",
        eval_steps=500,
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,  # Mixed precision training
        gradient_accumulation_steps=4,  # Effective batch size = batch_size * gradient_accumulation_steps
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )

Finally, let's train the model and analyze the results:

 trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )
    
    # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    fold_results.append(results)
    
    # Clear GPU memory
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

This implementation uses cross-validation techniques from sklearn but adapts them for the memory and computation needs of LLMs. By loading models from scratch in each fold and using memory-efficient training settings, you can run comprehensive validation even with modest hardware.

LLM Cross-Validation Technique #2: Implementing Time-Series Cross-Validation for Temporal Language Data

Time-series cross-validation requires a different approach than standard k-fold when working with temporal language data. The key challenge is respecting time order—future data shouldn't inform predictions about the past. This becomes especially important for optimizing LLMs with cross-validation on temporal data.

Rolling-origin cross-validation works best here. This method creates multiple training/validation splits that maintain chronological order while making the most of available data. Unlike standard k-fold, each training set includes observations from time 1 to k, while validation uses observations from time k+1 to k+n.

For an LLM trained on news articles, you'd start with older articles for initial training, then progressively add newer articles for subsequent training iterations while validating on even newer content. This preserves the temporal integrity essential for news content generation.

Here's a practical implementation of time-series cross-validation for temporal language data using pandas, numpy, torch, and transformers libraries:

import pandas as pd
import numpy as np
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
from datetime import datetime, timedelta

# Load temporal dataset (assume it has timestamps)
df = pd.read_csv("temporal_language_data.csv")
df["timestamp"] = pd.to_datetime(df["timestamp"])
df = df.sort_values("timestamp")  # Sort by time

# Convert to HF dataset
from datasets import Dataset
dataset = Dataset.from_pandas(df)

# Configure rolling window validation
window_size = timedelta(days=30)  # Training window
horizon = timedelta(days=7)      # Validation window
start_date = df["timestamp"].min()
end_date = df["timestamp"].max() - horizon  # Leave time for final validation

Next, let's set up the model and prepare for our rolling-origin validation:

fold_results = []
current_date = start_date

# Load model and tokenizer
model_name = "facebook/opt-350m"
tokenizer = AutoTokenizer.from_pretrained(model_name)

# Implement rolling-origin cross validation
fold = 0
while current_date + window_size < end_date:
    fold += 1
    print(f"Training fold {fold}")
    
    # Define training window
    train_start = start_date
    train_end = current_date + window_size
    
    # Define validation window 
    val_start = train_end
    val_end = val_start + horizon
    
    # Create training and validation masks
    train_mask = (df["timestamp"] >= train_start) & (df["timestamp"] < train_end)
    val_mask = (df["timestamp"] >= val_start) & (df["timestamp"] < val_end)
    
    train_indices = df[train_mask].index.tolist()
    val_indices = df[val_mask].index.tolist()
    
    # Skip if not enough validation data
    if len(val_indices) < 10:
        current_date += horizon
        continue

Now, let's set up the training for each time window:

# Create datasets for this fold
    train_dataset = dataset.select(train_indices)
    val_dataset = dataset.select(val_indices)
    
    # Initialize model
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training
    training_args = TrainingArguments(
        output_dir=f"./results/time_fold-{fold}",
        evaluation_strategy="epoch",
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )
    
    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )

Finally, let's train, evaluate, and analyze the results:

 # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    
    # Add timestamp info to results
    results["train_start"] = train_start
    results["train_end"] = train_end
    results["val_start"] = val_start
    results["val_end"] = val_end
    
    fold_results.append(results)
    
    # Move forward
    current_date += horizon
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Time-series cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

# Plot performance over time
import matplotlib.pyplot as plt
plt.figure(figsize=(12, 6))
plt.plot([r["val_end"] for r in fold_results], [r["eval_loss"] for r in fold_results])
plt.xlabel("Validation End Date")
plt.ylabel("Loss")
plt.title("Model Performance Over Time")
plt.savefig("temporal_performance.png")

This implementation maintains the temporal integrity of your data by ensuring that models are always trained on past data and validated on future data, simulating how they'll be used in production.

In addition, financial text analysis works particularly well with this approach. When implementing time-aware validation on financial news data, set up consistent validation windows (perhaps quarterly) that align with financial reporting cycles. This helps your model detect semantic shifts in terminology that happen during economic changes.

Time-series cross-validation teaches your model to learn from the past while being tested on the future—exactly how it will work in production. For any language model dealing with time-sensitive content, optimizing LLMs with cross-validation using this methodology should be your default rather than standard k-fold techniques.

LLM Cross-Validation Technique #3: Implementing Group K-Fold for Preventing Data Leakage in LLMs

Data leakage poses a serious challenge when evaluating language models. It happens when information sneaks between training and validation sets, artificially inflating performance metrics, including precision and recall.

Group k-fold validation solves this by keeping related data together. With conversation data, all messages from the same conversation should stay in the same fold. For document analysis, all content from the same author should remain grouped to prevent the model from "cheating" by recognizing writing patterns.

Here's a practical implementation of group k-fold cross-validation to prevent data leakage in LLMs:

from sklearn.model_selection import GroupKFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import pandas as pd
import numpy as np

# Load dataset with group identifiers
df = pd.read_csv("conversation_dataset.csv")
# Assume df has columns: 'text', 'group_id' (conversation_id, author_id, etc.)

# Convert to HF dataset
from datasets import Dataset
dataset = Dataset.from_pandas(df)

# Configure group k-fold cross validation
k_folds = 5
group_kfold = GroupKFold(n_splits=k_folds)
groups = df['group_id'].values

# Load model and tokenizer
model_name = "facebook/opt-350m"
tokenizer = AutoTokenizer.from_pretrained(model_name)

# Track metrics across folds
fold_results = []

Now, let's implement the group k-fold validation loop:

# Implement group k-fold cross validation
for fold, (train_idx, val_idx) in enumerate(group_kfold.split(df, groups=groups)):
    print(f"Training fold {fold+1}/{k_folds}")
    
    # Split data
    train_dataset = dataset.select(train_idx)
    val_dataset = dataset.select(val_idx)
    
    # Check group distribution
    train_groups = set(df.iloc[train_idx]['group_id'])
    val_groups = set(df.iloc[val_idx]['group_id'])
    print(f"Training on {len(train_groups)} groups, validating on {len(val_groups)} groups")
    print(f"Group overlap check (should be 0): {len(train_groups.intersection(val_groups))}")
    
    # Initialize model
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training
    training_args = TrainingArguments(
        output_dir=f"./results/group_fold-{fold}",
        evaluation_strategy="steps",
        eval_steps=500,
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )

Next, let's train the model and perform group-specific analysis:

 trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )
    
    # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    fold_results.append(results)
    
    # Analyze group-specific performance
    val_groups_list = list(val_groups)
    if len(val_groups_list) > 10:  # Sample if too many groups
        val_groups_sample = np.random.choice(val_groups_list, 10, replace=False)
    else:
        val_groups_sample = val_groups_list
        
    group_performance = {}
    for group in val_groups_sample:
        group_indices = df[df['group_id'] == group].index
        group_indices = [i for i in group_indices if i in val_idx]  # Keep only validation indices
        group_dataset = dataset.select(group_indices)
        
        if len(group_dataset) > 0:
            group_results = trainer.evaluate(eval_dataset=group_dataset)
            group_performance[group] = group_results["eval_loss"]

Finally, let's analyze and summarize the results:

 print("Group-specific performance:")
    for group, loss in group_performance.items():
        print(f"Group {group}: Loss = {loss:.4f}")
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Group k-fold cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

This implementation ensures that related data points stay together in the same fold, preventing data leakage that could artificially inflate your model's performance metrics and lead to overconfidence in its capabilities.

Configuration parameters matter significantly. Choose k values (typically 5-10) that balance computational cost with statistical reliability. Ensure each fold contains samples from multiple groups to maintain representative distributions. Also, stratify within groups if class imbalance exists.

Proper cross-validation implementation requires additional effort but delivers honest performance metrics. A slight decrease in reported performance is actually good news—it means you're getting a more accurate picture of how your model will perform on genuinely new data in production.

LLM Cross-Validation Technique #4: Implementing Nested Cross-Validation for LLM Hyperparameter Tuning

Nested cross-validation provides a powerful solution when you need both accurate AI model evaluation and optimal hyperparameter selection for LLM fine-tuning. This technique is among the top AI evaluation methods for ensuring reliable performance. The technique uses two loops:

An inner loop for hyperparameter optimization
An outer loop for performance estimation, preventing the selection process from skewing your evaluations

To implement nested CV, first set up your data partitioning with an outer k-fold split (typically k=5 or k=10). For each outer fold, run a complete hyperparameter optimization using k-fold CV on the training portion.

Then evaluate the best hyperparameter configuration on the held-out test fold. This separation matters, as nested CV produces more reliable performance estimates than single-loop validation when tuning fine-tuning hyperparameters.

Here's a practical implementation of nested cross-validation for LLM hyperparameter tuning using Optuna:

from sklearn.model_selection import KFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import numpy as np
import optuna
from datasets import Dataset
import pandas as pd

# Load dataset
df = pd.read_csv("your_dataset.csv")
dataset = Dataset.from_pandas(df)

# Configure outer cross validation
outer_k = 5
outer_kf = KFold(n_splits=outer_k, shuffle=True, random_state=42)

# Configure inner cross validation
inner_k = 3  # Use fewer folds for inner loop to save computation

Next, let's define the objective function for hyperparameter optimization:

# Define hyperparameter search space
def create_optuna_objective(train_dataset, inner_kf):
    def objective(trial):
        # Define hyperparameter search space
        learning_rate = trial.suggest_float("learning_rate", 1e-6, 1e-4, log=True)
        weight_decay = trial.suggest_float("weight_decay", 1e-3, 1e-1, log=True)
        batch_size = trial.suggest_categorical("batch_size", [4, 8, 16])
        
        # Define model and tokenizer
        model_name = "facebook/opt-350m"
        tokenizer = AutoTokenizer.from_pretrained(model_name)
        
        # Inner k-fold for hyperparameter tuning
        inner_fold_results = []
        
        for inner_fold, (inner_train_idx, inner_val_idx) in enumerate(inner_kf.split(train_dataset)):
            # Only run a subset of inner folds if trial is not promising
            if inner_fold > 0 and np.mean(inner_fold_results) > trial.study.best_value * 1.2:
                # Early stopping if performance is significantly worse than best so far
                break
                
            inner_train_data = train_dataset.select(inner_train_idx)
            inner_val_data = train_dataset.select(inner_val_idx)
            
            # Initialize model
            model = AutoModelForCausalLM.from_pretrained(model_name)
            
            # Configure training with trial hyperparameters
            training_args = TrainingArguments(
                output_dir=f"./results/trial-{trial.number}/fold-{inner_fold}",
                evaluation_strategy="epoch",
                learning_rate=learning_rate,
                weight_decay=weight_decay,
                per_device_train_batch_size=batch_size,
                per_device_eval_batch_size=batch_size,
                num_train_epochs=1,
                fp16=True,
                save_total_limit=1,
                load_best_model_at_end=True,
            )
            
            trainer = Trainer(
                model=model,
                args=training_args,
                train_dataset=inner_train_data,
                eval_dataset=inner_val_data,
            )
            
            # Train and evaluate
            trainer.train()
            results = trainer.evaluate()
            inner_fold_results.append(results["eval_loss"])
            
            # Clean up
            del model, trainer
            torch.cuda.empty_cache()
        
        # Return mean loss across inner folds
        mean_inner_loss = np.mean(inner_fold_results)
        return mean_inner_loss
    
    return objective

Now, let's implement the outer loop of our nested cross-validation:

# Store outer fold results
outer_fold_results = []

# Implement nested cross validation
for outer_fold, (outer_train_idx, outer_test_idx) in enumerate(outer_kf.split(dataset)):
    print(f"Outer fold {outer_fold+1}/{outer_k}")
    
    # Split data for this outer fold
    outer_train_dataset = dataset.select(outer_train_idx)
    outer_test_dataset = dataset.select(outer_test_idx)
    
    # Create inner k-fold splits on the outer training data
    inner_kf = KFold(n_splits=inner_k, shuffle=True, random_state=43)
    
    # Create Optuna study for hyperparameter optimization
    objective = create_optuna_objective(outer_train_dataset, inner_kf)
    study = optuna.create_study(direction="minimize")
    study.optimize(objective, n_trials=20)  # Adjust number of trials based on computation budget
    
    # Get best hyperparameters
    best_params = study.best_params
    print(f"Best hyperparameters: {best_params}")

Finally, let's train the final model with the best hyperparameters and evaluate results:

# Train final model with best hyperparameters on the entire outer training set
    model_name = "facebook/opt-350m"
    tokenizer = AutoTokenizer.from_pretrained(model_name)
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    training_args = TrainingArguments(
        output_dir=f"./results/outer_fold-{outer_fold}",
        evaluation_strategy="epoch",
        learning_rate=best_params["learning_rate"],
        weight_decay=best_params["weight_decay"],
        per_device_train_batch_size=best_params["batch_size"],
        per_device_eval_batch_size=best_params["batch_size"],
        num_train_epochs=2,  # Train longer for final model
        fp16=True,
    )
    
    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=outer_train_dataset,
        eval_dataset=outer_test_dataset,
    )
    
    # Train and evaluate final model on this outer fold
    trainer.train()
    results = trainer.evaluate()
    
    # Store results
    results["best_params"] = best_params
    outer_fold_results.append(results)
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze nested cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in outer_fold_results])
std_loss = np.std([r["eval_loss"] for r in outer_fold_results])
print(f"Nested cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

# Analyze best hyperparameters
for i, result in enumerate(outer_fold_results):
    print(f"Fold {i+1} best hyperparameters: {result['best_params']}")

This implementation efficiently finds optimal hyperparameters while providing unbiased estimates of model performance. The nested structure ensures that hyperparameter selection doesn't contaminate your final performance assessment, giving you more reliable insights into how your model will perform in production.

Focus your hyperparameter tuning where it counts most. Learning rate typically affects LLM fine-tuning performance the most, followed by batch size and training steps

For computational efficiency, try implementing early stopping in your inner loop to cut off unpromising hyperparameter combinations. Progressive pruning approaches, where you evaluate candidates on smaller data subsets first, can dramatically reduce computation time.

When implementing the outer loop, keep preprocessing consistent across all folds. Any transformations like normalization or tokenization must be performed independently within each fold to prevent data leakage. This detail is easy to overlook but critical for valid performance estimates.

Track your results systematically across both loops, recording not just final performance but also training dynamics. This comprehensive approach gives valuable insights into your model's behavior across different hyperparameter configurations and data splits, helping you build more robust LLMs for your specific applications.

Elevate Your LLM Performance With Galileo

Effective cross-validation for LLMs requires a comprehensive approach combining careful data splitting, domain-specific benchmarking, and continuous monitoring of model performance across various dimensions.

Galileo tackles the unique challenges of optimizing LLMs with cross-validation by providing an end-to-end solution that connects experimental evaluation with production-ready AI systems:

Get started with Galileo today to see how our tools can help you build more robust, reliable, and effective language models.

Picture this: you're responsible for optimizing LLMs for making crucial decisions that affect thousands of users every day. How confident are you in their performance?

The truth is, traditional validation methods that work for regular machine learning models just don't cut it when dealing with generative AI.

We recently explored this topic on our Chain of Thought podcast, where industry experts shared practical insights and real-world implementation strategies.

What is Cross-Validation for LLMs?

LLM Cross-Validation Technique #1: Implementing K-Fold Cross-Validation for Optimizing LLMs

Here's a practical approach that balances thoroughness with computational efficiency.

This ensures each fold contains a representative mix of your diverse prompt-response pairs, preventing situations where performance varies wildly between folds due to ML data blindspots.

Implement Computational Efficiency Tricks

Here's a practical implementation of k-fold cross-validation for optimizing LLMs with cross-validation using Hugging Face Transformers:

from sklearn.model_selection import KFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import numpy as np

# Load model and tokenizer
model_name = "facebook/opt-350m"  # Use smaller model for cross validation
tokenizer = AutoTokenizer.from_pretrained(model_name)
dataset = load_your_dataset()  # Your dataset loading function

# Configure k-fold cross validation
k_folds = 5
kf = KFold(n_splits=k_folds, shuffle=True, random_state=42)

# Track metrics across folds
fold_results = []

Now, let's set up the training loop for each fold:

for fold, (train_idx, val_idx) in enumerate(kf.split(dataset)):
    print(f"Training fold {fold+1}/{k_folds}")
    
    # Split data
    train_dataset = dataset.select(train_idx)
    val_dataset = dataset.select(val_idx)
    
    # Initialize model from checkpoint (prevents memory issues)
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training with memory efficiency in mind
    training_args = TrainingArguments(
        output_dir=f"./results/fold-{fold}",
        evaluation_strategy="steps",
        eval_steps=500,
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,  # Mixed precision training
        gradient_accumulation_steps=4,  # Effective batch size = batch_size * gradient_accumulation_steps
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )

Finally, let's train the model and analyze the results:

 trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )
    
    # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    fold_results.append(results)
    
    # Clear GPU memory
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

LLM Cross-Validation Technique #2: Implementing Time-Series Cross-Validation for Temporal Language Data

Here's a practical implementation of time-series cross-validation for temporal language data using pandas, numpy, torch, and transformers libraries:

import pandas as pd
import numpy as np
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
from datetime import datetime, timedelta

# Load temporal dataset (assume it has timestamps)
df = pd.read_csv("temporal_language_data.csv")
df["timestamp"] = pd.to_datetime(df["timestamp"])
df = df.sort_values("timestamp")  # Sort by time

# Convert to HF dataset
from datasets import Dataset
dataset = Dataset.from_pandas(df)

# Configure rolling window validation
window_size = timedelta(days=30)  # Training window
horizon = timedelta(days=7)      # Validation window
start_date = df["timestamp"].min()
end_date = df["timestamp"].max() - horizon  # Leave time for final validation

Next, let's set up the model and prepare for our rolling-origin validation:

fold_results = []
current_date = start_date

# Load model and tokenizer
model_name = "facebook/opt-350m"
tokenizer = AutoTokenizer.from_pretrained(model_name)

# Implement rolling-origin cross validation
fold = 0
while current_date + window_size < end_date:
    fold += 1
    print(f"Training fold {fold}")
    
    # Define training window
    train_start = start_date
    train_end = current_date + window_size
    
    # Define validation window 
    val_start = train_end
    val_end = val_start + horizon
    
    # Create training and validation masks
    train_mask = (df["timestamp"] >= train_start) & (df["timestamp"] < train_end)
    val_mask = (df["timestamp"] >= val_start) & (df["timestamp"] < val_end)
    
    train_indices = df[train_mask].index.tolist()
    val_indices = df[val_mask].index.tolist()
    
    # Skip if not enough validation data
    if len(val_indices) < 10:
        current_date += horizon
        continue

Now, let's set up the training for each time window:

# Create datasets for this fold
    train_dataset = dataset.select(train_indices)
    val_dataset = dataset.select(val_indices)
    
    # Initialize model
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training
    training_args = TrainingArguments(
        output_dir=f"./results/time_fold-{fold}",
        evaluation_strategy="epoch",
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )
    
    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )

Finally, let's train, evaluate, and analyze the results:

 # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    
    # Add timestamp info to results
    results["train_start"] = train_start
    results["train_end"] = train_end
    results["val_start"] = val_start
    results["val_end"] = val_end
    
    fold_results.append(results)
    
    # Move forward
    current_date += horizon
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Time-series cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

# Plot performance over time
import matplotlib.pyplot as plt
plt.figure(figsize=(12, 6))
plt.plot([r["val_end"] for r in fold_results], [r["eval_loss"] for r in fold_results])
plt.xlabel("Validation End Date")
plt.ylabel("Loss")
plt.title("Model Performance Over Time")
plt.savefig("temporal_performance.png")

This implementation maintains the temporal integrity of your data by ensuring that models are always trained on past data and validated on future data, simulating how they'll be used in production.

LLM Cross-Validation Technique #3: Implementing Group K-Fold for Preventing Data Leakage in LLMs

Here's a practical implementation of group k-fold cross-validation to prevent data leakage in LLMs:

from sklearn.model_selection import GroupKFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import pandas as pd
import numpy as np

# Load dataset with group identifiers
df = pd.read_csv("conversation_dataset.csv")
# Assume df has columns: 'text', 'group_id' (conversation_id, author_id, etc.)

# Convert to HF dataset
from datasets import Dataset
dataset = Dataset.from_pandas(df)

# Configure group k-fold cross validation
k_folds = 5
group_kfold = GroupKFold(n_splits=k_folds)
groups = df['group_id'].values

# Load model and tokenizer
model_name = "facebook/opt-350m"
tokenizer = AutoTokenizer.from_pretrained(model_name)

# Track metrics across folds
fold_results = []

Now, let's implement the group k-fold validation loop:

# Implement group k-fold cross validation
for fold, (train_idx, val_idx) in enumerate(group_kfold.split(df, groups=groups)):
    print(f"Training fold {fold+1}/{k_folds}")
    
    # Split data
    train_dataset = dataset.select(train_idx)
    val_dataset = dataset.select(val_idx)
    
    # Check group distribution
    train_groups = set(df.iloc[train_idx]['group_id'])
    val_groups = set(df.iloc[val_idx]['group_id'])
    print(f"Training on {len(train_groups)} groups, validating on {len(val_groups)} groups")
    print(f"Group overlap check (should be 0): {len(train_groups.intersection(val_groups))}")
    
    # Initialize model
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training
    training_args = TrainingArguments(
        output_dir=f"./results/group_fold-{fold}",
        evaluation_strategy="steps",
        eval_steps=500,
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )

Next, let's train the model and perform group-specific analysis:

 trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )
    
    # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    fold_results.append(results)
    
    # Analyze group-specific performance
    val_groups_list = list(val_groups)
    if len(val_groups_list) > 10:  # Sample if too many groups
        val_groups_sample = np.random.choice(val_groups_list, 10, replace=False)
    else:
        val_groups_sample = val_groups_list
        
    group_performance = {}
    for group in val_groups_sample:
        group_indices = df[df['group_id'] == group].index
        group_indices = [i for i in group_indices if i in val_idx]  # Keep only validation indices
        group_dataset = dataset.select(group_indices)
        
        if len(group_dataset) > 0:
            group_results = trainer.evaluate(eval_dataset=group_dataset)
            group_performance[group] = group_results["eval_loss"]

Finally, let's analyze and summarize the results:

 print("Group-specific performance:")
    for group, loss in group_performance.items():
        print(f"Group {group}: Loss = {loss:.4f}")
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Group k-fold cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

LLM Cross-Validation Technique #4: Implementing Nested Cross-Validation for LLM Hyperparameter Tuning

An inner loop for hyperparameter optimization
An outer loop for performance estimation, preventing the selection process from skewing your evaluations

Here's a practical implementation of nested cross-validation for LLM hyperparameter tuning using Optuna:

from sklearn.model_selection import KFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import numpy as np
import optuna
from datasets import Dataset
import pandas as pd

# Load dataset
df = pd.read_csv("your_dataset.csv")
dataset = Dataset.from_pandas(df)

# Configure outer cross validation
outer_k = 5
outer_kf = KFold(n_splits=outer_k, shuffle=True, random_state=42)

# Configure inner cross validation
inner_k = 3  # Use fewer folds for inner loop to save computation

Next, let's define the objective function for hyperparameter optimization:

# Define hyperparameter search space
def create_optuna_objective(train_dataset, inner_kf):
    def objective(trial):
        # Define hyperparameter search space
        learning_rate = trial.suggest_float("learning_rate", 1e-6, 1e-4, log=True)
        weight_decay = trial.suggest_float("weight_decay", 1e-3, 1e-1, log=True)
        batch_size = trial.suggest_categorical("batch_size", [4, 8, 16])
        
        # Define model and tokenizer
        model_name = "facebook/opt-350m"
        tokenizer = AutoTokenizer.from_pretrained(model_name)
        
        # Inner k-fold for hyperparameter tuning
        inner_fold_results = []
        
        for inner_fold, (inner_train_idx, inner_val_idx) in enumerate(inner_kf.split(train_dataset)):
            # Only run a subset of inner folds if trial is not promising
            if inner_fold > 0 and np.mean(inner_fold_results) > trial.study.best_value * 1.2:
                # Early stopping if performance is significantly worse than best so far
                break
                
            inner_train_data = train_dataset.select(inner_train_idx)
            inner_val_data = train_dataset.select(inner_val_idx)
            
            # Initialize model
            model = AutoModelForCausalLM.from_pretrained(model_name)
            
            # Configure training with trial hyperparameters
            training_args = TrainingArguments(
                output_dir=f"./results/trial-{trial.number}/fold-{inner_fold}",
                evaluation_strategy="epoch",
                learning_rate=learning_rate,
                weight_decay=weight_decay,
                per_device_train_batch_size=batch_size,
                per_device_eval_batch_size=batch_size,
                num_train_epochs=1,
                fp16=True,
                save_total_limit=1,
                load_best_model_at_end=True,
            )
            
            trainer = Trainer(
                model=model,
                args=training_args,
                train_dataset=inner_train_data,
                eval_dataset=inner_val_data,
            )
            
            # Train and evaluate
            trainer.train()
            results = trainer.evaluate()
            inner_fold_results.append(results["eval_loss"])
            
            # Clean up
            del model, trainer
            torch.cuda.empty_cache()
        
        # Return mean loss across inner folds
        mean_inner_loss = np.mean(inner_fold_results)
        return mean_inner_loss
    
    return objective

Now, let's implement the outer loop of our nested cross-validation:

# Store outer fold results
outer_fold_results = []

# Implement nested cross validation
for outer_fold, (outer_train_idx, outer_test_idx) in enumerate(outer_kf.split(dataset)):
    print(f"Outer fold {outer_fold+1}/{outer_k}")
    
    # Split data for this outer fold
    outer_train_dataset = dataset.select(outer_train_idx)
    outer_test_dataset = dataset.select(outer_test_idx)
    
    # Create inner k-fold splits on the outer training data
    inner_kf = KFold(n_splits=inner_k, shuffle=True, random_state=43)
    
    # Create Optuna study for hyperparameter optimization
    objective = create_optuna_objective(outer_train_dataset, inner_kf)
    study = optuna.create_study(direction="minimize")
    study.optimize(objective, n_trials=20)  # Adjust number of trials based on computation budget
    
    # Get best hyperparameters
    best_params = study.best_params
    print(f"Best hyperparameters: {best_params}")

Finally, let's train the final model with the best hyperparameters and evaluate results:

# Train final model with best hyperparameters on the entire outer training set
    model_name = "facebook/opt-350m"
    tokenizer = AutoTokenizer.from_pretrained(model_name)
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    training_args = TrainingArguments(
        output_dir=f"./results/outer_fold-{outer_fold}",
        evaluation_strategy="epoch",
        learning_rate=best_params["learning_rate"],
        weight_decay=best_params["weight_decay"],
        per_device_train_batch_size=best_params["batch_size"],
        per_device_eval_batch_size=best_params["batch_size"],
        num_train_epochs=2,  # Train longer for final model
        fp16=True,
    )
    
    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=outer_train_dataset,
        eval_dataset=outer_test_dataset,
    )
    
    # Train and evaluate final model on this outer fold
    trainer.train()
    results = trainer.evaluate()
    
    # Store results
    results["best_params"] = best_params
    outer_fold_results.append(results)
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze nested cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in outer_fold_results])
std_loss = np.std([r["eval_loss"] for r in outer_fold_results])
print(f"Nested cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

# Analyze best hyperparameters
for i, result in enumerate(outer_fold_results):
    print(f"Fold {i+1} best hyperparameters: {result['best_params']}")

Focus your hyperparameter tuning where it counts most. Learning rate typically affects LLM fine-tuning performance the most, followed by batch size and training steps

Elevate Your LLM Performance With Galileo

Galileo tackles the unique challenges of optimizing LLMs with cross-validation by providing an end-to-end solution that connects experimental evaluation with production-ready AI systems:

Get started with Galileo today to see how our tools can help you build more robust, reliable, and effective language models.

Picture this: you're responsible for optimizing LLMs for making crucial decisions that affect thousands of users every day. How confident are you in their performance?

The truth is, traditional validation methods that work for regular machine learning models just don't cut it when dealing with generative AI.

We recently explored this topic on our Chain of Thought podcast, where industry experts shared practical insights and real-world implementation strategies.

What is Cross-Validation for LLMs?

LLM Cross-Validation Technique #1: Implementing K-Fold Cross-Validation for Optimizing LLMs

Here's a practical approach that balances thoroughness with computational efficiency.

This ensures each fold contains a representative mix of your diverse prompt-response pairs, preventing situations where performance varies wildly between folds due to ML data blindspots.

Implement Computational Efficiency Tricks

Here's a practical implementation of k-fold cross-validation for optimizing LLMs with cross-validation using Hugging Face Transformers:

from sklearn.model_selection import KFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import numpy as np

# Load model and tokenizer
model_name = "facebook/opt-350m"  # Use smaller model for cross validation
tokenizer = AutoTokenizer.from_pretrained(model_name)
dataset = load_your_dataset()  # Your dataset loading function

# Configure k-fold cross validation
k_folds = 5
kf = KFold(n_splits=k_folds, shuffle=True, random_state=42)

# Track metrics across folds
fold_results = []

Now, let's set up the training loop for each fold:

for fold, (train_idx, val_idx) in enumerate(kf.split(dataset)):
    print(f"Training fold {fold+1}/{k_folds}")
    
    # Split data
    train_dataset = dataset.select(train_idx)
    val_dataset = dataset.select(val_idx)
    
    # Initialize model from checkpoint (prevents memory issues)
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training with memory efficiency in mind
    training_args = TrainingArguments(
        output_dir=f"./results/fold-{fold}",
        evaluation_strategy="steps",
        eval_steps=500,
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,  # Mixed precision training
        gradient_accumulation_steps=4,  # Effective batch size = batch_size * gradient_accumulation_steps
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )

Finally, let's train the model and analyze the results:

 trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )
    
    # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    fold_results.append(results)
    
    # Clear GPU memory
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

LLM Cross-Validation Technique #2: Implementing Time-Series Cross-Validation for Temporal Language Data

Here's a practical implementation of time-series cross-validation for temporal language data using pandas, numpy, torch, and transformers libraries:

import pandas as pd
import numpy as np
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
from datetime import datetime, timedelta

# Load temporal dataset (assume it has timestamps)
df = pd.read_csv("temporal_language_data.csv")
df["timestamp"] = pd.to_datetime(df["timestamp"])
df = df.sort_values("timestamp")  # Sort by time

# Convert to HF dataset
from datasets import Dataset
dataset = Dataset.from_pandas(df)

# Configure rolling window validation
window_size = timedelta(days=30)  # Training window
horizon = timedelta(days=7)      # Validation window
start_date = df["timestamp"].min()
end_date = df["timestamp"].max() - horizon  # Leave time for final validation

Next, let's set up the model and prepare for our rolling-origin validation:

fold_results = []
current_date = start_date

# Load model and tokenizer
model_name = "facebook/opt-350m"
tokenizer = AutoTokenizer.from_pretrained(model_name)

# Implement rolling-origin cross validation
fold = 0
while current_date + window_size < end_date:
    fold += 1
    print(f"Training fold {fold}")
    
    # Define training window
    train_start = start_date
    train_end = current_date + window_size
    
    # Define validation window 
    val_start = train_end
    val_end = val_start + horizon
    
    # Create training and validation masks
    train_mask = (df["timestamp"] >= train_start) & (df["timestamp"] < train_end)
    val_mask = (df["timestamp"] >= val_start) & (df["timestamp"] < val_end)
    
    train_indices = df[train_mask].index.tolist()
    val_indices = df[val_mask].index.tolist()
    
    # Skip if not enough validation data
    if len(val_indices) < 10:
        current_date += horizon
        continue

Now, let's set up the training for each time window:

# Create datasets for this fold
    train_dataset = dataset.select(train_indices)
    val_dataset = dataset.select(val_indices)
    
    # Initialize model
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training
    training_args = TrainingArguments(
        output_dir=f"./results/time_fold-{fold}",
        evaluation_strategy="epoch",
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )
    
    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )

Finally, let's train, evaluate, and analyze the results:

 # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    
    # Add timestamp info to results
    results["train_start"] = train_start
    results["train_end"] = train_end
    results["val_start"] = val_start
    results["val_end"] = val_end
    
    fold_results.append(results)
    
    # Move forward
    current_date += horizon
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Time-series cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

# Plot performance over time
import matplotlib.pyplot as plt
plt.figure(figsize=(12, 6))
plt.plot([r["val_end"] for r in fold_results], [r["eval_loss"] for r in fold_results])
plt.xlabel("Validation End Date")
plt.ylabel("Loss")
plt.title("Model Performance Over Time")
plt.savefig("temporal_performance.png")

This implementation maintains the temporal integrity of your data by ensuring that models are always trained on past data and validated on future data, simulating how they'll be used in production.

LLM Cross-Validation Technique #3: Implementing Group K-Fold for Preventing Data Leakage in LLMs

Here's a practical implementation of group k-fold cross-validation to prevent data leakage in LLMs:

from sklearn.model_selection import GroupKFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import pandas as pd
import numpy as np

# Load dataset with group identifiers
df = pd.read_csv("conversation_dataset.csv")
# Assume df has columns: 'text', 'group_id' (conversation_id, author_id, etc.)

# Convert to HF dataset
from datasets import Dataset
dataset = Dataset.from_pandas(df)

# Configure group k-fold cross validation
k_folds = 5
group_kfold = GroupKFold(n_splits=k_folds)
groups = df['group_id'].values

# Load model and tokenizer
model_name = "facebook/opt-350m"
tokenizer = AutoTokenizer.from_pretrained(model_name)

# Track metrics across folds
fold_results = []

Now, let's implement the group k-fold validation loop:

# Implement group k-fold cross validation
for fold, (train_idx, val_idx) in enumerate(group_kfold.split(df, groups=groups)):
    print(f"Training fold {fold+1}/{k_folds}")
    
    # Split data
    train_dataset = dataset.select(train_idx)
    val_dataset = dataset.select(val_idx)
    
    # Check group distribution
    train_groups = set(df.iloc[train_idx]['group_id'])
    val_groups = set(df.iloc[val_idx]['group_id'])
    print(f"Training on {len(train_groups)} groups, validating on {len(val_groups)} groups")
    print(f"Group overlap check (should be 0): {len(train_groups.intersection(val_groups))}")
    
    # Initialize model
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training
    training_args = TrainingArguments(
        output_dir=f"./results/group_fold-{fold}",
        evaluation_strategy="steps",
        eval_steps=500,
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )

Next, let's train the model and perform group-specific analysis:

 trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )
    
    # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    fold_results.append(results)
    
    # Analyze group-specific performance
    val_groups_list = list(val_groups)
    if len(val_groups_list) > 10:  # Sample if too many groups
        val_groups_sample = np.random.choice(val_groups_list, 10, replace=False)
    else:
        val_groups_sample = val_groups_list
        
    group_performance = {}
    for group in val_groups_sample:
        group_indices = df[df['group_id'] == group].index
        group_indices = [i for i in group_indices if i in val_idx]  # Keep only validation indices
        group_dataset = dataset.select(group_indices)
        
        if len(group_dataset) > 0:
            group_results = trainer.evaluate(eval_dataset=group_dataset)
            group_performance[group] = group_results["eval_loss"]

Finally, let's analyze and summarize the results:

 print("Group-specific performance:")
    for group, loss in group_performance.items():
        print(f"Group {group}: Loss = {loss:.4f}")
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Group k-fold cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

LLM Cross-Validation Technique #4: Implementing Nested Cross-Validation for LLM Hyperparameter Tuning

An inner loop for hyperparameter optimization
An outer loop for performance estimation, preventing the selection process from skewing your evaluations

Here's a practical implementation of nested cross-validation for LLM hyperparameter tuning using Optuna:

from sklearn.model_selection import KFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import numpy as np
import optuna
from datasets import Dataset
import pandas as pd

# Load dataset
df = pd.read_csv("your_dataset.csv")
dataset = Dataset.from_pandas(df)

# Configure outer cross validation
outer_k = 5
outer_kf = KFold(n_splits=outer_k, shuffle=True, random_state=42)

# Configure inner cross validation
inner_k = 3  # Use fewer folds for inner loop to save computation

Next, let's define the objective function for hyperparameter optimization:

# Define hyperparameter search space
def create_optuna_objective(train_dataset, inner_kf):
    def objective(trial):
        # Define hyperparameter search space
        learning_rate = trial.suggest_float("learning_rate", 1e-6, 1e-4, log=True)
        weight_decay = trial.suggest_float("weight_decay", 1e-3, 1e-1, log=True)
        batch_size = trial.suggest_categorical("batch_size", [4, 8, 16])
        
        # Define model and tokenizer
        model_name = "facebook/opt-350m"
        tokenizer = AutoTokenizer.from_pretrained(model_name)
        
        # Inner k-fold for hyperparameter tuning
        inner_fold_results = []
        
        for inner_fold, (inner_train_idx, inner_val_idx) in enumerate(inner_kf.split(train_dataset)):
            # Only run a subset of inner folds if trial is not promising
            if inner_fold > 0 and np.mean(inner_fold_results) > trial.study.best_value * 1.2:
                # Early stopping if performance is significantly worse than best so far
                break
                
            inner_train_data = train_dataset.select(inner_train_idx)
            inner_val_data = train_dataset.select(inner_val_idx)
            
            # Initialize model
            model = AutoModelForCausalLM.from_pretrained(model_name)
            
            # Configure training with trial hyperparameters
            training_args = TrainingArguments(
                output_dir=f"./results/trial-{trial.number}/fold-{inner_fold}",
                evaluation_strategy="epoch",
                learning_rate=learning_rate,
                weight_decay=weight_decay,
                per_device_train_batch_size=batch_size,
                per_device_eval_batch_size=batch_size,
                num_train_epochs=1,
                fp16=True,
                save_total_limit=1,
                load_best_model_at_end=True,
            )
            
            trainer = Trainer(
                model=model,
                args=training_args,
                train_dataset=inner_train_data,
                eval_dataset=inner_val_data,
            )
            
            # Train and evaluate
            trainer.train()
            results = trainer.evaluate()
            inner_fold_results.append(results["eval_loss"])
            
            # Clean up
            del model, trainer
            torch.cuda.empty_cache()
        
        # Return mean loss across inner folds
        mean_inner_loss = np.mean(inner_fold_results)
        return mean_inner_loss
    
    return objective

Now, let's implement the outer loop of our nested cross-validation:

# Store outer fold results
outer_fold_results = []

# Implement nested cross validation
for outer_fold, (outer_train_idx, outer_test_idx) in enumerate(outer_kf.split(dataset)):
    print(f"Outer fold {outer_fold+1}/{outer_k}")
    
    # Split data for this outer fold
    outer_train_dataset = dataset.select(outer_train_idx)
    outer_test_dataset = dataset.select(outer_test_idx)
    
    # Create inner k-fold splits on the outer training data
    inner_kf = KFold(n_splits=inner_k, shuffle=True, random_state=43)
    
    # Create Optuna study for hyperparameter optimization
    objective = create_optuna_objective(outer_train_dataset, inner_kf)
    study = optuna.create_study(direction="minimize")
    study.optimize(objective, n_trials=20)  # Adjust number of trials based on computation budget
    
    # Get best hyperparameters
    best_params = study.best_params
    print(f"Best hyperparameters: {best_params}")

Finally, let's train the final model with the best hyperparameters and evaluate results:

# Train final model with best hyperparameters on the entire outer training set
    model_name = "facebook/opt-350m"
    tokenizer = AutoTokenizer.from_pretrained(model_name)
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    training_args = TrainingArguments(
        output_dir=f"./results/outer_fold-{outer_fold}",
        evaluation_strategy="epoch",
        learning_rate=best_params["learning_rate"],
        weight_decay=best_params["weight_decay"],
        per_device_train_batch_size=best_params["batch_size"],
        per_device_eval_batch_size=best_params["batch_size"],
        num_train_epochs=2,  # Train longer for final model
        fp16=True,
    )
    
    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=outer_train_dataset,
        eval_dataset=outer_test_dataset,
    )
    
    # Train and evaluate final model on this outer fold
    trainer.train()
    results = trainer.evaluate()
    
    # Store results
    results["best_params"] = best_params
    outer_fold_results.append(results)
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze nested cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in outer_fold_results])
std_loss = np.std([r["eval_loss"] for r in outer_fold_results])
print(f"Nested cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

# Analyze best hyperparameters
for i, result in enumerate(outer_fold_results):
    print(f"Fold {i+1} best hyperparameters: {result['best_params']}")

Focus your hyperparameter tuning where it counts most. Learning rate typically affects LLM fine-tuning performance the most, followed by batch size and training steps

Elevate Your LLM Performance With Galileo

Galileo tackles the unique challenges of optimizing LLMs with cross-validation by providing an end-to-end solution that connects experimental evaluation with production-ready AI systems:

Get started with Galileo today to see how our tools can help you build more robust, reliable, and effective language models.

Picture this: you're responsible for optimizing LLMs for making crucial decisions that affect thousands of users every day. How confident are you in their performance?

The truth is, traditional validation methods that work for regular machine learning models just don't cut it when dealing with generative AI.

We recently explored this topic on our Chain of Thought podcast, where industry experts shared practical insights and real-world implementation strategies.

What is Cross-Validation for LLMs?

LLM Cross-Validation Technique #1: Implementing K-Fold Cross-Validation for Optimizing LLMs

Here's a practical approach that balances thoroughness with computational efficiency.

This ensures each fold contains a representative mix of your diverse prompt-response pairs, preventing situations where performance varies wildly between folds due to ML data blindspots.

Implement Computational Efficiency Tricks

Here's a practical implementation of k-fold cross-validation for optimizing LLMs with cross-validation using Hugging Face Transformers:

from sklearn.model_selection import KFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import numpy as np

# Load model and tokenizer
model_name = "facebook/opt-350m"  # Use smaller model for cross validation
tokenizer = AutoTokenizer.from_pretrained(model_name)
dataset = load_your_dataset()  # Your dataset loading function

# Configure k-fold cross validation
k_folds = 5
kf = KFold(n_splits=k_folds, shuffle=True, random_state=42)

# Track metrics across folds
fold_results = []

Now, let's set up the training loop for each fold:

for fold, (train_idx, val_idx) in enumerate(kf.split(dataset)):
    print(f"Training fold {fold+1}/{k_folds}")
    
    # Split data
    train_dataset = dataset.select(train_idx)
    val_dataset = dataset.select(val_idx)
    
    # Initialize model from checkpoint (prevents memory issues)
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training with memory efficiency in mind
    training_args = TrainingArguments(
        output_dir=f"./results/fold-{fold}",
        evaluation_strategy="steps",
        eval_steps=500,
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,  # Mixed precision training
        gradient_accumulation_steps=4,  # Effective batch size = batch_size * gradient_accumulation_steps
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )

Finally, let's train the model and analyze the results:

 trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )
    
    # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    fold_results.append(results)
    
    # Clear GPU memory
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

LLM Cross-Validation Technique #2: Implementing Time-Series Cross-Validation for Temporal Language Data

Here's a practical implementation of time-series cross-validation for temporal language data using pandas, numpy, torch, and transformers libraries:

import pandas as pd
import numpy as np
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
from datetime import datetime, timedelta

# Load temporal dataset (assume it has timestamps)
df = pd.read_csv("temporal_language_data.csv")
df["timestamp"] = pd.to_datetime(df["timestamp"])
df = df.sort_values("timestamp")  # Sort by time

# Convert to HF dataset
from datasets import Dataset
dataset = Dataset.from_pandas(df)

# Configure rolling window validation
window_size = timedelta(days=30)  # Training window
horizon = timedelta(days=7)      # Validation window
start_date = df["timestamp"].min()
end_date = df["timestamp"].max() - horizon  # Leave time for final validation

Next, let's set up the model and prepare for our rolling-origin validation:

fold_results = []
current_date = start_date

# Load model and tokenizer
model_name = "facebook/opt-350m"
tokenizer = AutoTokenizer.from_pretrained(model_name)

# Implement rolling-origin cross validation
fold = 0
while current_date + window_size < end_date:
    fold += 1
    print(f"Training fold {fold}")
    
    # Define training window
    train_start = start_date
    train_end = current_date + window_size
    
    # Define validation window 
    val_start = train_end
    val_end = val_start + horizon
    
    # Create training and validation masks
    train_mask = (df["timestamp"] >= train_start) & (df["timestamp"] < train_end)
    val_mask = (df["timestamp"] >= val_start) & (df["timestamp"] < val_end)
    
    train_indices = df[train_mask].index.tolist()
    val_indices = df[val_mask].index.tolist()
    
    # Skip if not enough validation data
    if len(val_indices) < 10:
        current_date += horizon
        continue

Now, let's set up the training for each time window:

# Create datasets for this fold
    train_dataset = dataset.select(train_indices)
    val_dataset = dataset.select(val_indices)
    
    # Initialize model
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training
    training_args = TrainingArguments(
        output_dir=f"./results/time_fold-{fold}",
        evaluation_strategy="epoch",
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )
    
    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )

Finally, let's train, evaluate, and analyze the results:

 # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    
    # Add timestamp info to results
    results["train_start"] = train_start
    results["train_end"] = train_end
    results["val_start"] = val_start
    results["val_end"] = val_end
    
    fold_results.append(results)
    
    # Move forward
    current_date += horizon
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Time-series cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

# Plot performance over time
import matplotlib.pyplot as plt
plt.figure(figsize=(12, 6))
plt.plot([r["val_end"] for r in fold_results], [r["eval_loss"] for r in fold_results])
plt.xlabel("Validation End Date")
plt.ylabel("Loss")
plt.title("Model Performance Over Time")
plt.savefig("temporal_performance.png")

This implementation maintains the temporal integrity of your data by ensuring that models are always trained on past data and validated on future data, simulating how they'll be used in production.

LLM Cross-Validation Technique #3: Implementing Group K-Fold for Preventing Data Leakage in LLMs

Here's a practical implementation of group k-fold cross-validation to prevent data leakage in LLMs:

from sklearn.model_selection import GroupKFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import pandas as pd
import numpy as np

# Load dataset with group identifiers
df = pd.read_csv("conversation_dataset.csv")
# Assume df has columns: 'text', 'group_id' (conversation_id, author_id, etc.)

# Convert to HF dataset
from datasets import Dataset
dataset = Dataset.from_pandas(df)

# Configure group k-fold cross validation
k_folds = 5
group_kfold = GroupKFold(n_splits=k_folds)
groups = df['group_id'].values

# Load model and tokenizer
model_name = "facebook/opt-350m"
tokenizer = AutoTokenizer.from_pretrained(model_name)

# Track metrics across folds
fold_results = []

Now, let's implement the group k-fold validation loop:

# Implement group k-fold cross validation
for fold, (train_idx, val_idx) in enumerate(group_kfold.split(df, groups=groups)):
    print(f"Training fold {fold+1}/{k_folds}")
    
    # Split data
    train_dataset = dataset.select(train_idx)
    val_dataset = dataset.select(val_idx)
    
    # Check group distribution
    train_groups = set(df.iloc[train_idx]['group_id'])
    val_groups = set(df.iloc[val_idx]['group_id'])
    print(f"Training on {len(train_groups)} groups, validating on {len(val_groups)} groups")
    print(f"Group overlap check (should be 0): {len(train_groups.intersection(val_groups))}")
    
    # Initialize model
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    # Configure training
    training_args = TrainingArguments(
        output_dir=f"./results/group_fold-{fold}",
        evaluation_strategy="steps",
        eval_steps=500,
        learning_rate=5e-5,
        weight_decay=0.01,
        fp16=True,
        per_device_train_batch_size=4,
        per_device_eval_batch_size=4,
        num_train_epochs=1,
    )

Next, let's train the model and perform group-specific analysis:

 trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=train_dataset,
        eval_dataset=val_dataset,
    )
    
    # Train and evaluate
    trainer.train()
    results = trainer.evaluate()
    fold_results.append(results)
    
    # Analyze group-specific performance
    val_groups_list = list(val_groups)
    if len(val_groups_list) > 10:  # Sample if too many groups
        val_groups_sample = np.random.choice(val_groups_list, 10, replace=False)
    else:
        val_groups_sample = val_groups_list
        
    group_performance = {}
    for group in val_groups_sample:
        group_indices = df[df['group_id'] == group].index
        group_indices = [i for i in group_indices if i in val_idx]  # Keep only validation indices
        group_dataset = dataset.select(group_indices)
        
        if len(group_dataset) > 0:
            group_results = trainer.evaluate(eval_dataset=group_dataset)
            group_performance[group] = group_results["eval_loss"]

Finally, let's analyze and summarize the results:

 print("Group-specific performance:")
    for group, loss in group_performance.items():
        print(f"Group {group}: Loss = {loss:.4f}")
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in fold_results])
std_loss = np.std([r["eval_loss"] for r in fold_results])
print(f"Group k-fold cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

LLM Cross-Validation Technique #4: Implementing Nested Cross-Validation for LLM Hyperparameter Tuning

An inner loop for hyperparameter optimization
An outer loop for performance estimation, preventing the selection process from skewing your evaluations

Here's a practical implementation of nested cross-validation for LLM hyperparameter tuning using Optuna:

from sklearn.model_selection import KFold
from transformers import AutoModelForCausalLM, AutoTokenizer, Trainer, TrainingArguments
import torch
import numpy as np
import optuna
from datasets import Dataset
import pandas as pd

# Load dataset
df = pd.read_csv("your_dataset.csv")
dataset = Dataset.from_pandas(df)

# Configure outer cross validation
outer_k = 5
outer_kf = KFold(n_splits=outer_k, shuffle=True, random_state=42)

# Configure inner cross validation
inner_k = 3  # Use fewer folds for inner loop to save computation

Next, let's define the objective function for hyperparameter optimization:

# Define hyperparameter search space
def create_optuna_objective(train_dataset, inner_kf):
    def objective(trial):
        # Define hyperparameter search space
        learning_rate = trial.suggest_float("learning_rate", 1e-6, 1e-4, log=True)
        weight_decay = trial.suggest_float("weight_decay", 1e-3, 1e-1, log=True)
        batch_size = trial.suggest_categorical("batch_size", [4, 8, 16])
        
        # Define model and tokenizer
        model_name = "facebook/opt-350m"
        tokenizer = AutoTokenizer.from_pretrained(model_name)
        
        # Inner k-fold for hyperparameter tuning
        inner_fold_results = []
        
        for inner_fold, (inner_train_idx, inner_val_idx) in enumerate(inner_kf.split(train_dataset)):
            # Only run a subset of inner folds if trial is not promising
            if inner_fold > 0 and np.mean(inner_fold_results) > trial.study.best_value * 1.2:
                # Early stopping if performance is significantly worse than best so far
                break
                
            inner_train_data = train_dataset.select(inner_train_idx)
            inner_val_data = train_dataset.select(inner_val_idx)
            
            # Initialize model
            model = AutoModelForCausalLM.from_pretrained(model_name)
            
            # Configure training with trial hyperparameters
            training_args = TrainingArguments(
                output_dir=f"./results/trial-{trial.number}/fold-{inner_fold}",
                evaluation_strategy="epoch",
                learning_rate=learning_rate,
                weight_decay=weight_decay,
                per_device_train_batch_size=batch_size,
                per_device_eval_batch_size=batch_size,
                num_train_epochs=1,
                fp16=True,
                save_total_limit=1,
                load_best_model_at_end=True,
            )
            
            trainer = Trainer(
                model=model,
                args=training_args,
                train_dataset=inner_train_data,
                eval_dataset=inner_val_data,
            )
            
            # Train and evaluate
            trainer.train()
            results = trainer.evaluate()
            inner_fold_results.append(results["eval_loss"])
            
            # Clean up
            del model, trainer
            torch.cuda.empty_cache()
        
        # Return mean loss across inner folds
        mean_inner_loss = np.mean(inner_fold_results)
        return mean_inner_loss
    
    return objective

Now, let's implement the outer loop of our nested cross-validation:

# Store outer fold results
outer_fold_results = []

# Implement nested cross validation
for outer_fold, (outer_train_idx, outer_test_idx) in enumerate(outer_kf.split(dataset)):
    print(f"Outer fold {outer_fold+1}/{outer_k}")
    
    # Split data for this outer fold
    outer_train_dataset = dataset.select(outer_train_idx)
    outer_test_dataset = dataset.select(outer_test_idx)
    
    # Create inner k-fold splits on the outer training data
    inner_kf = KFold(n_splits=inner_k, shuffle=True, random_state=43)
    
    # Create Optuna study for hyperparameter optimization
    objective = create_optuna_objective(outer_train_dataset, inner_kf)
    study = optuna.create_study(direction="minimize")
    study.optimize(objective, n_trials=20)  # Adjust number of trials based on computation budget
    
    # Get best hyperparameters
    best_params = study.best_params
    print(f"Best hyperparameters: {best_params}")

Finally, let's train the final model with the best hyperparameters and evaluate results:

# Train final model with best hyperparameters on the entire outer training set
    model_name = "facebook/opt-350m"
    tokenizer = AutoTokenizer.from_pretrained(model_name)
    model = AutoModelForCausalLM.from_pretrained(model_name)
    
    training_args = TrainingArguments(
        output_dir=f"./results/outer_fold-{outer_fold}",
        evaluation_strategy="epoch",
        learning_rate=best_params["learning_rate"],
        weight_decay=best_params["weight_decay"],
        per_device_train_batch_size=best_params["batch_size"],
        per_device_eval_batch_size=best_params["batch_size"],
        num_train_epochs=2,  # Train longer for final model
        fp16=True,
    )
    
    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=outer_train_dataset,
        eval_dataset=outer_test_dataset,
    )
    
    # Train and evaluate final model on this outer fold
    trainer.train()
    results = trainer.evaluate()
    
    # Store results
    results["best_params"] = best_params
    outer_fold_results.append(results)
    
    # Clean up
    del model, trainer
    torch.cuda.empty_cache()

# Analyze nested cross-validation results
mean_loss = np.mean([r["eval_loss"] for r in outer_fold_results])
std_loss = np.std([r["eval_loss"] for r in outer_fold_results])
print(f"Nested cross-validation loss: {mean_loss:.4f} ± {std_loss:.4f}")

# Analyze best hyperparameters
for i, result in enumerate(outer_fold_results):
    print(f"Fold {i+1} best hyperparameters: {result['best_params']}")

Focus your hyperparameter tuning where it counts most. Learning rate typically affects LLM fine-tuning performance the most, followed by batch size and training steps

Elevate Your LLM Performance With Galileo

Galileo tackles the unique challenges of optimizing LLMs with cross-validation by providing an end-to-end solution that connects experimental evaluation with production-ready AI systems:

Get started with Galileo today to see how our tools can help you build more robust, reliable, and effective language models.

Conor Bronsdon