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This is a medium difficulty Machine Learning question, commonly asked during Technical Screen rounds at Applied Intuition.

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This question is commonly asked for Machine Learning Engineer candidates at Applied Intuition during technical interviews.

Implement correct attention masking

Last updated: Mar 29, 2026

Quick Overview

This question evaluates a candidate's competency in attention mechanisms for autoregressive Transformers, specifically the implementation of causal and padding masks, their combination in multi-head attention, and the ability to diagnose masking-related training anomalies.

Applied Intuition

Sep 6, 2025, 12:00 AM

Machine Learning Engineer

Technical Screen

Machine Learning

Autoregressive Transformer: Correct Attention Masking with Padding

Context: You are implementing decoder self-attention for an autoregressive Transformer where input sequences in a batch are right-padded to a common length. You must prevent attention to future tokens and exclude padded positions.

Task:

Implement a causal mask that prevents attending to future tokens.
Implement a padding mask that prevents attending to padded positions.
Show how to combine and apply these masks in multi-head attention.
Explain common bugs, how they appear in loss/accuracy, and how to test for them.

Assumptions:

Batch-first tensors: shape (B, T, D).
Right padding. An attention_mask of shape (B, T) uses 1 for real tokens and 0 for padding (or equivalently, you have pad_token_id and input_ids).
PyTorch is available.

Solution

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