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Decagon interview notes, page 2 of 4

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Most of these Decagon write-ups come from Software Engineers (30), then AI Engineers (1). The most reported rounds are the technical phone screen (22), the system design round (8) and the behavioral / leadership round (1).

31 interview notes · updated Jul 2026

Decagon·Software Engineer·Technical Phone Screen

May 2026
Interviewed for a software engineer role at Decagon and got a classic CPU scheduling / call stack problem. Nothing too wild but it required you to actually think through the edge cases carefully.
  • Given a list of log strings in the format '{function_id}:{start|end}:{timestamp}' for n functions running on a single-threaded CPU, compute the exclusive execution time for each function (i.e. time on CPU excluding any time spent inside nested calls).

“The stack simulation part clicked pretty fast for me.”

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Decagon·AI Engineer·Technical Phone Screen

May 2026
Interviewed for an AI Engineer role at Decagon and got a coding problem involving function call logs and exclusive execution time. Pretty standard stack-based problem but the nested call tracking tripped me up a bit.
  • Given a list of function call logs on a single-threaded CPU, where each log contains a function ID, whether it's a start or end event, and a timestamp, compute the exclusive execution time for each function. Nested calls should not count toward the caller's time. Return an array indexed by function ID.

“My first instinct was to just accumulate raw time per function and I completely forgot to subtract nested call durations.”

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Decagon·Software Engineer·Technical Phone Screen

May 2026
Got a stack-based simulation problem at Decagon for a software engineer role. Nothing too wild but it required you to actually think through the execution model carefully.
  • Given n functions running on a single-threaded CPU and a list of logs in the format 'function_id:start|end:timestamp', compute the exclusive execution time for each function (i.e. time spent in that function excluding any time spent in functions it called).

“The stack approach clicked pretty fast but I kept second-guessing the timestamp math.”

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Decagon·Software Engineer·Technical Phone Screen

May 2026
Decagon software engineer interview with a coding problem centered on a rolling-window CSAT tracker. Pretty much one meaty design-plus-implementation question, and they wanted you to talk through tradeoffs out loud the whole time.
  • Design and implement a CSATTracker class that records customer satisfaction scores and returns a rolling average over a configurable time window. Discuss your data structure choice and the time and space complexity of each operation.

“I went with a deque of (timestamp, conversation_id, score) tuples sorted by arrival time, which felt right.”

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Decagon·Software Engineer·Onsite - System Design / Architecture

May 2026
Decagon system design round for a software engineer role. The whole thing was one big open-ended question about building a domain-specific chatbot from scratch, covering basically every layer of the stack. Dense but kind of interesting if you're into LLM infra.
  • Design a complete end-to-end chatbot system for a single enterprise customer operating within one domain, covering ingestion and indexing of their content, retrieval with vector search and reranking, LLM selection and prompting, conversation memory, tool-use orchestration, safety guardrails, evaluation, and deployment topology.

“This is a monster of a question.”

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Decagon·Software Engineer·Onsite - Behavioral / Leadership

May 2026
Cultural fit round at Decagon for a software engineering role. Pretty conversational, no coding, just a lot of back-and-forth about how you work with people and why you want to be there specifically.
  • Why do you want to work at this company and this team in particular?
  • What kind of work environment do you do your best work in?
  • How do you approach collaboration and communication across a team?
  • Tell me about a time you disagreed with a peer or manager and how you handled it.
  • Can you give an example of how your behavior or approach reflects the company's stated values or principles?

“You really can't wing this one.”

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Decagon·Software Engineer·Technical Phone Screen

May 2026
Interviewed for a Software Engineer role at Decagon and got a classic stack-based CPU scheduling problem. Nothing too exotic but it required careful thinking about how timestamps work, especially the inclusive end semantics.
  • Given logs from a single-threaded CPU running n functions, where each log entry marks a function start or end with a timestamp, compute the exclusive execution time for each function (i.e., time in its own body, not counting time spent in callees).

“The stack simulation part clicked pretty fast for me.”

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Decagon·Software Engineer·Technical Phone Screen

May 2026
45-minute phone screen at Decagon for a software engineer role, one coding question with follow-ups. Managed to pass despite introducing two bugs along the way, which the interviewer was gracious enough to let me debug through during testing.
  • Design a CSAT (Customer Satisfaction) tracker class that accepts a fixed window size, records conversation scores (1-5) with unique IDs and strictly increasing timestamps, and returns the average score across all entries within the active time window, rounded to 2 decimal places.
  • Follow-up: add an update method that changes a conversation's score if it still falls within the active window, and does nothing if the conversation has expired. The original timestamp and ordering must be preserved.
  • Follow-up: given an integer p, compute the p-th percentile score across all conversations currently in the active window.

“I'd seen this problem before and still shipped two bugs.”

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Decagon·Software Engineer·Onsite - System Design / Architecture

May 2026
System design round at Decagon for a software engineering role. The whole thing was basically one long deep dive into a past project, and they were not interested in staying surface level.
  • Walk us through a past project in deep technical detail, including the overall architecture, the specific parts you owned, the design decisions you made and why, how data flowed through the system, how you thought about scaling, and what failure modes you had to deal with.

“They literally handed me a whiteboard marker and said draw it.”

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Decagon·Software Engineer·Onsite - System Design / Architecture

Jun 2026
System design round at Decagon for a software engineer role, focused entirely on building an AI Gateway service. The question had a lot of moving parts and the interviewer kept pushing on specific subsystems rather than letting me stay high-level.
  • Design an AI Gateway service that sits between internal application services and external model providers like OpenAI, Anthropic, and Google. How would you handle routing, rate limiting, observability, and resilience?

“This felt manageable at first and then the follow-ups kept coming.”

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