Decagon · Software Engineer
Updated · 2026-09-22

Decagon Software Engineer
Interview Guide

THE 60-SECOND BRIEF

As a Software Engineer at Decagon, you will play a foundational role in building the leading conversational AI platform that empowers global brands to deliver concierge customer experiences. Your work directly contributes to intelligent, human-like AI agents that resolve millions of customer inquiries across chat, email, and voice channels in any language. Operating in a high-velocity environment, you will drive the systems that coordinate complex model reasoning, scale low-latency data and voice infrastructure, and shape the developer platform that allows your peers to ship with confidence. This role sits at the intersection of extreme scale, real-time distributed systems, and cutting-edge applied AI. You will contribute to critical problem spaces such as core infrastructure, data pipelines, ML serving, agent orchestration, and real-time telephony stacks.

This guide is scoped to a Software Engineer candidate at Decagon.

Decagon candidates report 3 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

AlgorithmsData StructuresDSA (Algorithms & Data Structures) / Logic Reasoning

22 min read

Practice 21 Software Engineer prompts
18Company bank questionsSnapshot · Sep 23, 2026 PT
3Candidate experiences ↗Read their reports
21Practice promptsAcross five skill areas

As a Software Engineer at Decagon, you will play a foundational role in building the leading conversational AI platform that empowers global brands to deliver concierge customer experiences. Your work directly contributes to intelligent, human-like AI agents that resolve millions of customer inquiries across chat, email, and voice channels in any language. Operating in a high-velocity environment, you will drive the systems that coordinate complex model reasoning, scale low-latency data and voice infrastructure, and shape the developer platform that allows your peers to ship with confidence. This role sits at the intersection of extreme scale, real-time distributed systems, and cutting-edge applied AI. You will contribute to critical problem spaces such as core infrastructure, data pipelines, ML serving, agent orchestration, and real-time telephony stacks. Whether you are tuning tight p95 and p99 latencies for LLM inference or architecting the execution engine that powers intelligent agents, your code will directly impact tier-one enterprise customers like Duolingo, Oura, Eventbrite, and Hertz. Expect a fast-paced, in-office culture driven by a shared commitment to excellence, momentum, and customer-centric problem solving. You will work alongside world-class engineering teams who value technical rigor, autonomy, and ownership.

01

Recruiter Screening

reported

Initial discussion with a recruiter about career goals, background, and alignment with the company's mission.

What to demonstrate

  • Initial discussion with a recruiter about career goals, background, and alignment with the company's mission
  • Depth in Algorithms

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.
Decagon Software Engineer candidate reports
02

Technical Assessments

reported

Series of coding rounds focusing on data structures and algorithms, threading, and language internals.

What to demonstrate

  • Series of coding rounds focusing on data structures and algorithms, threading, and language internals
  • Depth in Algorithms

How to prepare

  • Answer aloud and timed: Implement a shopping cart system for a cooking application with methods to add recipes, remove recipes, calculate total discounts based on ingredient quantities, and support undoing and redoing cart operations.
  • Answer aloud and timed: Solve challenging algorithmic problems involving basic and advanced data structures, focusing on efficiency and edge-case management.
Decagon Software Engineer candidate reports
03

Onsite Interview Loop

reported

Comprehensive onsite interviews featuring system design and domain-specific challenges.

What to demonstrate

  • Comprehensive onsite interviews featuring system design and domain-specific challenges
  • Depth in Algorithms

How to prepare

  • Answer aloud and timed: Write production-ready code in Python, TypeScript, or JavaScript that handles asynchronous operations cleanly.
  • Answer aloud and timed: Evaluates your ability to design scalable, fault-tolerant distributed systems with clear trade-offs around latency, consistency, and availability.
Decagon Software Engineer candidate reports

3 candidate reports. Individual accounts describe a particular role and hiring cycle.

Software Engineer

Decagon Software Engineer Interview Experience — CSAT Tracker Question on the Phone Screen

Technical Screen

I interviewed for 45 minutes and got one question. I'd solved it before, but I still wrote two bugs. Luckily I caught and fixed both while testing, and it passed in the end. Thanks to the interviewer for going easy on me. The question was the one that comes up most often for the phone screen: design a customer satisfaction (CSAT) tracking class. Scores are fixed in the range 1 to 5. __init__(self…

Read full experience
AI Engineer

Decagon AI Engineer Interview Experience — A Tic-Tac-Toe Sequence-Counting Problem in the Coding Round

Technical Screen

I recently interviewed for Decagon's AI Engineer role, first round (the coding round), and got a question that doesn't have an exact match on LeetCode, so I wanted to share it. Problem Two players take turns placing marks on a 3x3 board, X goes first, then O, alternating. A game is the entire sequence of moves from an empty board to the end of the game. The game ends immediately as soon as one si…

Read full experience
Software Engineer

Decagon Software Engineer Interview Experience — Shopping Cart Versioning, Then Rejected on Tic-Tac-Toe

Technical ScreenOutcome: rejected

Round 1 was the shopping cart problem that other interview reports have also mentioned, but part 2 seemed a bit different. You're building a shopping cart for a cooking app. Users can add recipes to their cart. Each recipe has a list of ingredients (e.g., Chicken, Garlic). When the same ingredient appears across multiple recipes, the total count qualifies for bulk discounts. Part 1 was the same a…

Read full experience

PracHub editorial advice for the preparation topics above.

01

Going into the loop without having done this.

Communicate your assumptions proactively: Interviewers at Decagon value collaborative problem solvers who think out loud. When presented with an ambiguous prompt or coding challenge, explicitly state your assumptions, verify edge cases, and talk through trade-offs before diving into implementation.

02

Going into the loop without having done this.

Embrace feedback and hints: If an interviewer offers a simplification or a nudge during a coding or system design round, do not view it as a penalty. Treat it as real-time engineering collaboration, incorporate the feedback smoothly, and explain how it alters your approach.

03

Going into the loop without having done this.

Focus on failure modes in design: When discussing system architecture, never stop at the happy path. Actively highlight potential bottlenecks, single points of failure, and how your design handles network partitions, traffic spikes, or upstream service degradation.

04

Going into the loop without having done this.

Demonstrate a winner's mindset: Reflect the company's core values by showing high agency, enthusiasm for solving hard technical problems, and a commitment to operational excellence and team success.

Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.

17 technical prompts0 include a worked solution

Focuses on your core algorithmic fluency, ability to write clean code under time constraints, and aptitude for

medium
Coding and Data Structures

Focuses on your core algorithmic fluency, ability to write clean code under time constraints, and aptitude for translating functional requirements into robust implementations.

Approach
  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.
Follow-up
  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Implement a shopping cart system for a cooking application with methods to add recipes, remove recipes, calcul

medium
Coding and Data Structures

Implement a shopping cart system for a cooking application with methods to add recipes, remove recipes, calculate total discounts based on ingredient quantities, and support undoing and redoing cart operations.

Approach
  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.
Follow-up
  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Solve challenging algorithmic problems involving basic and advanced data structures, focusing on efficiency an

medium
Coding and Data Structures

Solve challenging algorithmic problems involving basic and advanced data structures, focusing on efficiency and edge-case management.

Approach
  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.
Follow-up
  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write production-ready code in Python, TypeScript, or JavaScript that handles asynchronous operations cleanly.

medium
Coding and Data Structures

Write production-ready code in Python, TypeScript, or JavaScript that handles asynchronous operations cleanly.

Approach
  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.
Follow-up
  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Tests your deep understanding of language runtimes, threading models, and low-level system performance.

medium
Concurrency and Technical Fundamentals

Tests your deep understanding of language runtimes, threading models, and low-level system performance.

Approach
  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.
Follow-up
  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Explain and implement solutions involving threading, synchronization, and race condition avoidance in concurre

medium
Concurrency and Technical Fundamentals

Explain and implement solutions involving threading, synchronization, and race condition avoidance in concurrent environments.

Approach
  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.
Follow-up
  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Describe how asynchronous programming patterns behave under high load in Python or TypeScript.

medium
Concurrency and Technical Fundamentals

Describe how asynchronous programming patterns behave under high load in Python or TypeScript.

Approach
  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.
Follow-up
  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Optimize networking paths and apply smart caching or queuing to tune CPU, memory, and I/O for tight latency pe

medium
Concurrency and Technical Fundamentals

Optimize networking paths and apply smart caching or queuing to tune CPU, memory, and I/O for tight latency percentiles.

Approach
  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.
Follow-up
  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Built from the rounds and topics Decagon candidates report.

Small steps. Visible outcomes.0 / 7 completed
ONE WEEK · YOUR PACE

Prepare, practise & reflect

One practical outcome each day. Spend longer where you need it.

0 / 7 done
01Map the Decagon loop
  • Write out the reported sequence: Recruiter Screening, Technical Assessments, Onsite Interview Loop.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.

02Work Algorithms
  • Spend the session on Algorithms, which Decagon candidates report being tested on.
  • Write one worked example in Algorithms and time yourself on it.

Deliverable: One timed worked example in Algorithms.

03Work Data Structures
  • Spend the session on Data Structures, which Decagon candidates report being tested on.
  • Write one worked example in Data Structures and time yourself on it.

Deliverable: One timed worked example in Data Structures.

04Work DSA (Algorithms & Data Structures) / Logic Reasoning
  • Spend the session on DSA (Algorithms & Data Structures) / Logic Reasoning, which Decagon candidates report being tested on.
  • Write one worked example in DSA (Algorithms & Data Structures) / Logic Reasoning and time yourself on it.

Deliverable: One timed worked example in DSA (Algorithms & Data Structures) / Logic Reasoning.

05Answer out loud: Coding and Data Structures
  • Answer aloud, timed: Focuses on your core algorithmic fluency, ability to write clean code under time constraints, and aptitude for translating functional requirements into robust implementations.
  • Answer aloud, timed: Design a Customer Satisfaction (CSAT) tracking class with a fixed score range of 1 to 5, including a time window size, a method to record unique conversation IDs and scores with strictly increasing timestamps, and a way to calculate average scores or specified percentiles within active windows.

Deliverable: Spoken answers to 2 reported Coding and Data Structures question(s), under time.

06Answer out loud: System Design and Architecture
  • Answer aloud, timed: Evaluates your ability to design scalable, fault-tolerant distributed systems with clear trade-offs around latency, consistency, and availability.
  • Answer aloud, timed: Design a real-time messaging application akin to Slack, detailing message routing, data storage, and connection management.

Deliverable: Spoken answers to 2 reported System Design and Architecture question(s), under time.

07Answer out loud: Concurrency and Technical Fundamentals
  • Answer aloud, timed: Tests your deep understanding of language runtimes, threading models, and low-level system performance.
  • Answer aloud, timed: Explain and implement solutions involving threading, synchronization, and race condition avoidance in concurrent environments.

Deliverable: Spoken answers to 2 reported Concurrency and Technical Fundamentals question(s), under time.

Expand any day for tasks and deliverables. Your progress is saved on this device.

Behavioural rounds judge the decision you made and what it cost.

Assesses your communication skills, teamwork, alignment with company values, and approach to ambiguity.

medium
Behavioral and Culture Fit

Assesses your communication skills, teamwork, alignment with company values, and approach to ambiguity.

Approach
  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.
Follow-up
  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Why should we hire you?

medium
Behavioral and Culture Fit

Why should we hire you?

Approach
  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.
Follow-up
  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Tell me about a time you owned a large technical project end-to-end and handled unexpected roadblocks.

medium
Behavioral and Culture Fit

Tell me about a time you owned a large technical project end-to-end and handled unexpected roadblocks.

Approach
  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.
Follow-up
  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you prioritize competing engineering demands while maintaining relentless momentum?

medium
Behavioral and Culture Fit

How do you prioritize competing engineering demands while maintaining relentless momentum?

Approach
  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.
Follow-up
  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?
  • 01

    Assesses your communication skills, teamwork, alignment with company values, and approach to ambiguity.

  • 02

    Why should we hire you?

  • 03

    Tell me about a time you owned a large technical project end-to-end and handled unexpected roadblocks.

  • 04

    How do you prioritize competing engineering demands while maintaining relentless momentum?

PracHub preparation framework
How difficult are the technical interviews at Decagon?

The technical bar is high, and interviewers expect rigorous problem-solving and clean execution. You should expect LeetCode medium-to-hard coding problems alongside demanding system design and concurrency evaluations. Thorough preparation on fundamentals and time management during coding rounds is essential for success.

Decagon Software Engineer candidate reports
What is the typical interview timeline from initial screen to final offer?

The process typically moves swiftly over the course of two to four weeks, though scheduling multiple technical rounds and an onsite loop requires good coordination. Candidates should maintain open communication with their recruiter regarding scheduling pacing and any competing offers.

Decagon Software Engineer candidate reports
Does Decagon operate in a remote or in-office environment?

Decagon is an in-office company, anchored by a shared commitment to velocity, collaboration, and daily in-person interaction. Candidates should be prepared to work from the designated office locations, such as San Francisco or New York, where daily lunch, dinner, and snacks are provided.

Decagon Software Engineer candidate reports
What differentiates successful candidates in the interview loop?

Successful candidates stand out by communicating their thought process clearly, demonstrating intellectual humility when receiving hints, and designing systems with a strong emphasis on failure modes and operational simplicity. Aligning your answers with the company's core values—such as relentless momentum and customer obsession—also leaves a strong impression.

Decagon Software Engineer candidate reports
How should I prepare for the system design portion of the interview?

Focus on understanding how to scale distributed systems, optimize latency percentiles, and design robust telemetry and observability pipelines. Practice breaking down open-ended prompts into core requirements, data models, and scaling bottlenecks rather than relying on memorized architectures.

Decagon Software Engineer candidate reports
How hard is the Decagon interview?

Candidates most commonly rate Decagon interviews as medium, based on 41 reported interviews. About 68% of candidates who interview go on to receive an offer.

Decagon Software Engineer candidate reports
What topics does Decagon test in interviews?

Decagon interviews most often cover Large Language Models (LLMs), System Design, Algorithms, Data Structures, and Experimentation & Iterative Research Planning. The exact emphasis depends on the specific role you apply for.

Decagon Software Engineer candidate reports
Sources & methodology 3 sources ↗

Official role evidence, timestamped platform data and clearly labeled preparation advice.