OA - Banking System

The Banking System (or "In-Memory Banking Service") is a popular technical interview question used by Anthropic for software engineering roles. It typically tests your ability to handle stateful logic, concurrency, and evolving requirements in a 55-minute live-coding or system-design environment. Exponent +3 2 [6](https://prachub.com/interview-questions/design-an-in-memory-banking-service#:~:text=Quick%20Overview,initiating%20a%20transfer%20does%20not.%20() 3 4 8

Problem Statement Overview

You are tasked with designing and implementing an in-memory banking service that supports various financial operations. The system must manage account states, process transactions with specific temporal (timestamp) semantics, and handle complex edge cases. [6](https://prachub.com/interview-questions/design-an-in-memory-banking-service#:~:text=Quick%20Overview,initiating%20a%20transfer%20does%20not.%20() 9

Core Functional Requirements

The problem evolves through multiple levels, demanding functionality such as:

• Account Management: create_account(id, t), deposit(id, amount, t), and pay(id, amount, t) (with insufficient funds check).
• Transfers: transfer(src, dst, amount, t) (pending state) and accept_transfer(dst, transfer_id, t) (finalizing to account).
• Evolution: Later stages often introduce account merges and re-creations, requiring that IDs can be reused while preserving historical data.

Key Technical Challenges

• Temporal Logic: Managing operations with specific timestamps, often involving out-of-order events.
• State & Concurrency: Maintaining consistent account balances and potentially handling thread safety.
• Data Aggregation: Calculating metrics like "top Kcap K𝐾 most active accounts" based on finalized transfers. Reddit +1

How Anthropic Evaluates You

As noted in sources like Exponent and PracHub, the focus is on:

• Modularity: Designing for changing requirements, such as adding a merge feature.
• System Design: Handling trade-offs between consistency and performance.
• Safety Focus: Reflecting Anthropic's emphasis on reliability, similar to their AI safety principles. Exponent +4

Would you like to walk through a Python implementation for the basic account and transfer logic?

[0] - Anthropic Software Engineer Interview Guide 2026 - PracHub [1] - Top 30 Most Common Anthropic Interview Questions You Should ... [2] - Anthropic System Design Interview (2026 Guide) - Exponent [3] - 30+ Common Anthropic Interview Questions + Answers (by role) [4] - Anthropic Technical Interview (55 min CodeSignal) - Reddit [5] - Anthropic Staff Success Story - Hello Interview [6] - Design an in-memory banking service - Anthropic Questions [7] - Anthropic Software Engineer Interview Guide 2026 - PracHub [8] - How is AI transforming banking operations? - AIM Media House [9] - Design an in-memory banking service | Anthropic Interview Question [10] - Leetcode 2043. Simple Bank System