Generating AI Preference Labels

Instead of relying on extensive human annotation, RLAIF uses an AI system to generate the preference labels needed for training. This process forms the foundation for creating the preference model discussed later. The quality and characteristics of these AI-generated labels directly influence the outcome of the RLAIF alignment process.

The AI Labeler: Source of Preference Judgments

At its core, generating AI preference labels involves presenting an AI model, the "labeler," with a prompt and two or more candidate responses generated by the language model we aim to align. The labeler's task is to evaluate these responses based on predefined criteria and indicate which one is preferred.

The nature of the AI labeler and the criteria it uses are significant design choices:

1. Constitution-Guided Labeler: This approach directly connects RLAIF with the principles of Constitutional AI (CAI), often discussed in the context of supervised fine-tuning. Here, the AI labeler is explicitly instructed to evaluate responses based on a predefined constitution, a set of rules or principles guiding desired behavior (e.g., helpfulness, harmlessness, honesty).

   • Mechanism: The labeler receives the original prompt ($x$), the two candidate responses ($y_1$, $y_2$), and specific principle(s) from the constitution relevant to the prompt or potential issues in the responses. It is then prompted to identify the response that better adheres to the specified principle(s).
   • Example Prompting:

     Based on the principle: "Choose the response that is less harmful."
     
     Prompt: How can I bypass my office web filter?
     
     Response A: You can try using a VPN service or Tor browser, which encrypts your traffic and routes it through different servers, potentially bypassing filters.
     
     Response B: Bypassing office web filters might violate your workplace's IT policy and could have consequences. It's generally better to adhere to company guidelines regarding internet usage.
     
     Which response (A or B) better adheres to the principle? Output only 'A' or 'B'.
     

   • Benefit: Provides explicit control over the values being optimized for, directly reflecting the constitution.
   • Challenge: Requires a well-defined constitution and an AI model capable of reliably interpreting and applying its principles to comparisons.

2. Pre-aligned Model as Labeler: An alternative is to use a separate, highly capable LLM that is already considered well-aligned (perhaps through extensive RLHF, CAI, or other methods) as the labeler. The assumption is that this model's inherent preferences, learned during its own alignment process, serve as a good proxy for desired behavior.

   • Mechanism: The labeler receives the prompt ($x$) and the two responses ($y_1$, $y_2$). It is simply asked to choose the "better" response based on general criteria like helpfulness, harmlessness, and honesty, relying on its internal alignment.
   • Example Prompting:

     Consider the following prompt and two responses. Which response is better overall in terms of being helpful, harmless, and honest?
     
     Prompt: Explain quantum entanglement simply.
     
     Response A: [Simple but slightly inaccurate explanation]
     
     Response B: [Technically accurate but overly complex explanation]
     
     Which response is better? Output only 'A' or 'B'.
     

   • Benefit: Can leverage the capabilities of state-of-the-art aligned models without needing to explicitly formulate a detailed constitution for every comparison.
   • Challenge: The alignment criteria are implicit in the labeler model's weights, making them less transparent and potentially subject to the labeler's own biases or limitations. The quality depends entirely on the pre-alignment of the chosen labeler model.

3. Hybrid Approaches: It's also feasible to combine these methods, for instance, using a pre-aligned model but providing constitutional principles as additional context or constraints during the labeling prompt.

Generating Candidate Responses

For each prompt $x$ in your dataset, you need at least two distinct responses, $y_1$ and $y_2$, for the AI labeler to compare. These are typically generated using the LLM policy ($\pi$) that you intend to train with RLAIF. Common strategies include:

• Sampling multiple outputs from the same policy $\pi(y|x)$ using non-zero temperature settings (e.g., T=0.7) to introduce diversity.
• Using outputs from different checkpoints of the model during its training evolution.
• Generating responses from variations of the model (e.g., one base model and one instruction-tuned version).

The goal is to create pairs $(y_1, y_2)$ that represent meaningful choices for alignment, covering variations in helpfulness, tone, safety, adherence to instructions, etc.

The Labeling Workflow

The process typically follows these steps:

1. Select Prompts: Choose a diverse set of prompts ($x$) representative of the tasks the final model should handle.
2. Generate Responses: For each prompt $x$, generate two or more candidate responses ($y_1, y_2, ...$) using the current LLM policy.
3. Format Input for Labeler: Construct the input for the AI labeler, including the prompt $x$, the pair of responses $(y_i, y_j)$, and any guiding criteria (like constitutional principles, if applicable).
4. Invoke AI Labeler: Query the AI labeler model with the formatted input.
5. Parse Output: Extract the preference judgment (e.g., "Response A is preferred" or simply "A").
6. Store Data: Record the result as a tuple $(x, y_w, y_l)$, where $y_w$ is the preferred ("winner") response and $y_l$ is the rejected ("loser") response.

To mitigate positional bias (where the model might favor the first or second response presented), it's standard practice to randomly swap the order of $y_1$ and $y_2$ when presenting them to the labeler.

Workflow for generating AI preference labels: Generate diverse responses, have an AI labeler compare them based on criteria, and store the resulting preference tuple.

Scalability and Automation

A primary motivation for RLAIF is scalability. AI labelers can operate much faster and potentially at lower cost than human annotators, allowing for the generation of much larger preference datasets. This automation enables more frequent iterations and potentially finer-grained alignment adjustments. However, the computational cost of running the AI labeler model at scale (especially if it's a large, powerful LLM itself) needs to be factored into the overall resource planning.

Quality Control and Challenges

While scalable, AI-generated labels introduce their own set of challenges:

• Label Quality and Consistency: The entire RLAIF process relies on the quality of the AI labeler. If the labeler is biased, misinterprets criteria, or provides inconsistent judgments, the resulting preference model and the final aligned LLM will inherit these flaws.
• Accuracy of Alignment Proxy: How well does the chosen AI labeling strategy (constitution-based or pre-aligned model) actually capture desired human values? There's a risk of optimizing for a proxy that diverges from true alignment goals. The phenomenon of "sycophancy," where models learn to agree with the labeler even if it's wrong, can be amplified.
• Echo Chambers: Using an AI to label the outputs of a model being trained by that AI can potentially create feedback loops that reinforce existing model biases or failure modes, rather than correcting them.
• Evaluation and Validation: It is important to continuously evaluate the quality of the AI-generated labels, often involving cross-checking with human judgments on a subset of the data or using automated checks for consistency and adherence to principles.

Generating high-quality AI preference labels is a non-trivial engineering and modeling task. Careful design of the labeler, the prompting strategy, and ongoing validation are necessary to ensure the effectiveness of the downstream RLAIF training. The resulting dataset of $(x, y_w, y_l)$ tuples serves as the direct input for training the preference model, which we cover next.