# Joon Hee Lee

Member of Technical Staff at Cognition building Devin's multi-model harness (Devin Fusion); ex-Senior Staff Engineer and Poe Core Product lead at Quora  
Cognition  
Irvine, California, United States

## At Cognition

- Role: Member of Technical Staff (Engineering)
- Joined: May 2026
- How they joined: Directly
- Before Cognition: Senior Staff Software Engineer, Product Team Lead, Quora
- Overlapped before Cognition with other Cognition people at: Quora; Google; Caltech (https://www.autumn.ai/resources/cognition/worked-together)

## Identity
- LinkedIn: https://www.linkedin.com/in/joonheelee
- Domain: cognition.ai

## Notes
- Devin Fusion (launched 2026-06-29) was his first major project at Cognition: in his words, "Devin Fusion was the first major project I worked on after joining Cognition seven weeks ago." Fusion pairs a frontier lead model with a cheaper sidekick model. (https://www.linkedin.com/posts/joonheelee_devin-fusion-was-the-first-major-project-activity-7482555849337372672-4uiD)
- Authored the Cognition blog post "Making Fable Cheaper Than Opus" (2026-07-13): swapping Opus 4.8 for Fable 5 as Devin's lead model lowered the bill despite Fable costing 2x per token, because Fable delegates earlier; Fable + sidekick cost $1.86/run vs $2.04 for Opus + sidekick on FrontierCode 1.1, scoring 60.7 vs 54.6. (https://cognition.com/blog/making-fable-cheaper-than-opus)
- Joined Cognition as Member of Technical Staff in May 2026 after nearly nine years at Quora; LinkedIn headline reads "Building Devin @ Cognition". He came from Quora/Poe directly, not via Cognition's Windsurf acquisition. (https://www.linkedin.com/in/joonheelee)
- At Quora (Mar 2024-May 2026) he was Senior Staff Software Engineer and product lead for Poe's Core Product team of 20+ engineers, designers and data scientists, working directly with the CEO (Adam D'Angelo) on Poe's strategy, owning all AI/ML features, LLM quality/evaluation, cost and speed, and third-party model provider relationships. (https://www.linkedin.com/in/joonheelee)
- Was the first engineer and tech lead manager on Poe's ML team (Staff ML Engineer, Aug 2022-Mar 2024) and tech lead manager for the Quora Feed team - so his routing/cost work at Cognition continues years of balancing LLM quality, latency and cost across many providers on Poe. (https://www.linkedin.com/in/joonheelee)
- Current role is Member of Technical Staff at Cognition. (https://www.linkedin.com/in/joonheelee)
- Spoke on "The State of Model Routing - NVIDIA, Cognition, OpenRouter" (AI Engineer, published 2026-08-06), positioning him as Cognition's public voice on multi-model routing. (https://www.youtube.com/watch?v=QHBjufYK8TA)
- His Fable analysis ran 3,000 evaluation sessions across four configurations and found that in 81% of Fable-led runs the lead never made a code edit (vs 24% for Opus), and Opus made 4x more corrective edits at lead prices - evidence he works on agent delegation behaviour and eval methodology, not just routing infrastructure. (https://cognition.com/blog/making-fable-cheaper-than-opus)
- On Fusion he wrote that "Fable, for example, was much less of a micromanager than Opus or GPT 5.5. It also scoped the sidekick's work better and did a better job reviewing its code" and that "the best ones resemble good human management" - a management framing that echoes his years as a tech lead manager at Quora. (https://www.linkedin.com/posts/joonheelee_devin-fusion-was-the-first-major-project-activity-7482555849337372672-4uiD)
- Cognition's Devin Fusion launch post claims the multi-model harness keeps frontier and Fable 5-level performance at 60% lower cost on FrontierCode; Fusion uses lightweight classifiers for dynamic mid-session routing between the main agent and sidekick. (https://cognition.com/blog/devin-fusion)
- Publicly recruits for Cognition: "If this kind of work sounds interesting to you too, consider joining us at Cognition!". (https://www.linkedin.com/posts/joonheelee_devin-fusion-was-the-first-major-project-activity-7482555849337372672-4uiD)
- Credited under Research in the acknowledgements of Cognition's FrontierCode 1.1 benchmark post, alongside Eric Lu, Ben Pan, Fermi Ma, Jacob Teo and Silas Alberti; FrontierCode is the benchmark his Fusion and Fable results are measured on. (https://cognition.com/blog/frontier-code-1.1)
- Public headline says "Building Devin @ Cognition". (https://www.linkedin.com/in/joonheelee)
- His Poe profile @joon (bio "ML Engineer @ Quora working on Poe") lists 128 created bots, including AIQuartet, which consults four frontier models in parallel and merges one answer - an early multi-model ensemble that prefigures Devin Fusion. (https://poe.com/joon)
- Shared Cognition's SWE-1.7 model launch, writing: "Frontier intelligence + fast enough (1000 tok/s!) to keep you in flow state = an entirely different experience". (https://www.linkedin.com/posts/joonheelee_introducing-swe-17-the-most-capable-model-activity-7480679840589717504-BiIl)
- Announced Poe's no-code app creation: "Really excited to launch this! You can now create and share custom AI apps on Poe through vibe coding - no coding knowledge required!" (https://www.linkedin.com/posts/joonheelee_really-excited-to-launch-this-you-can-now-activity-7300212230216671233-3X95)
- Earlier Quora roles: Machine Learning Engineer (2018-2021) and Senior ML Engineer / tech lead for the Feed (recommender) team (2021-2022), after a 2017 software engineering internship at Quora. (https://www.linkedin.com/in/joonheelee)
- B.S. in Computer Science from Caltech (2014-2018), with a 2017 study-abroad semester at DTU (Technical University of Denmark) in Copenhagen. (https://www.linkedin.com/in/joonheelee)
- Built the Hacktech iOS app (2015-2016) for Caltech's student hackathon; open-source activity is on GitHub under the hatooku account (repos hatooku/Hacktech-iOS and hatooku/foodfeud, 2015-2016). (https://www.getprog.ai/profile/joon_lee_9364360)
- Product-focused machine learning engineer with experience in recommender systems and applications of generative AI; this comes from the profile summary and preserves the person's own positioning. (https://www.linkedin.com/in/joonheelee)
- The Fable post was picked up by Taiwanese tech press (Business Next, Yahoo TW), which described him as a Cognition engineer and reported the cost result, giving his first Cognition byline international reach. (https://fc.bnext.com.tw/articles/view/4816)
- Announced Poe's web launch in 2023: "Quora has just launched the web version of Poe that allows you to talk to AI in the fastest and easiest way." (https://www.linkedin.com/posts/joonheelee_poe-for-desktop-activity-7037607352040136704-hv8J)
- Software Engineering Intern at Google in 2016 and teaching assistant for Caltech's Computer Algorithms course in 2016. (https://www.linkedin.com/in/joonheelee)
- Previous roles include Senior Staff Software Engineer, Product Team Lead at Quora; Staff Machine Learning Engineer, Product Team Lead at Quora; Senior Machine Learning Engineer at Quora; Machine Learning Engineer at Quora; Software Engineering Intern at Quora; Software Engineering Intern at Google; Teaching Assistant, Computer Algorithms at Caltech; iOS Developer at Hacktech. (https://www.linkedin.com/in/joonheelee)
- Education history includes Bachelor’s Degree, Computer Science, Caltech; Computer Science, DTU - Technical University of Denmark. (https://www.linkedin.com/in/joonheelee)
- Previous roles include Member of Technical Staff at Cognition; Senior Staff Software Engineer, Product Team Lead at Quora; Staff Machine Learning Engineer, Product Team Lead at Quora; Senior Machine Learning Engineer at Quora; Machine Learning Engineer at Quora; Software Engineering Intern at Quora; Software Engineering Intern at Google; Teaching Assistant, Computer Algorithms at Caltech. (https://www.linkedin.com/in/joonheelee)
- Software intern at Caltech's Center for Data-Driven Discovery (2015); third-party profile summaries mention VR visualization work from his Caltech years. (https://www.linkedin.com/in/joonheelee)
- Based in Irvine, California, while his Cognition role is listed in San Francisco. (https://www.linkedin.com/in/joonheelee)
- Location is Irvine, California, United States. (https://www.linkedin.com/in/joonheelee)

## Experience
- Member of Technical Staff at Cognition - San Francisco, California, United States (May 2026 - Present)
- Senior Staff Software Engineer, Product Team Lead at Quora (Mar 2024 - May 2026): Product lead for Poe's Core Product team of 20+ product and AI engineers, designers, and data scientists. Work directly with the CEO to develop and execute Poe's product strategy and roadmap.

Ownership areas include:
• Core product features across all platforms (Web, iOS, Android)
• All AI/ML-powered features on Poe
• LLM quality & evaluation, costs, and speed
• Interfacing with third-party model providers
- Staff Machine Learning Engineer, Product Team Lead at Quora - Mountain View, California, United States (Aug 2022 - Mar 2024): • Tech lead manager for Quora Feed team
• First engineer and tech lead manager on Poe ML team
• Product team lead on Poe Core Product team
- Senior Machine Learning Engineer at Quora - Mountain View, California, United States (Jan 2021 - Aug 2022): Tech lead for Feed team
- Machine Learning Engineer at Quora - Mountain View, California, United States (Aug 2018 - Jan 2021)
- Software Engineering Intern at Quora - Mountain View, California, United States (Jun 2017 - Aug 2017)
- Software Engineering Intern at Google - San Francisco Bay Area (Jun 2016 - Sep 2016): Implemented a SiriKit extension for Google Wallet in Objective C to enable voice commands for sending and requesting payments.

Created a general client for Wallet app extensions to communicate with the backend API and the local database.

Designed and implemented new protocols and classes for Wallet SDK for use in other first-party apps.
- Teaching Assistant, Computer Algorithms at Caltech - Pasadena, CA (Mar 2016 - Jun 2016)
- iOS Developer at Hacktech - Pasadena, California (Sep 2015 - Feb 2016): Developed the official iOS application for Hacktech, Caltech's hackathon, using Xcode and Swift.

Utilized a Parse and customized the backend and push notification system using Cloud Code (Javascript).
- Software Intern at Center for Data-Driven Discovery - Pasadena, California (Mar 2015 - Dec 2015): Developed a virtual reality multi-dimensional data visualization program in C# using Unity3D and Oculus Rift and optimized the program through user tests

Created a networking framework for the program through Unity3D’s UNET system.

Ownership areas include:
• Core product features across all platforms (Web, iOS, Android)
• All AI/ML-powered features on Poe
• LLM quality & evaluation, costs, and speed
• Interfacing with third-party model providers
• First engineer and tech lead manager on Poe ML team
• Product team lead on Poe Core Product team

Created a general client for Wallet app extensions to communicate with the backend API and the local database.

Designed and implemented new protocols and classes for Wallet SDK for use in other first-party apps.

Utilized a Parse and customized the backend and push notification system using Cloud Code (Javascript).

Created a networking framework for the program through Unity3D’s UNET system.

## Education
- Caltech - Bachelor’s Degree, Computer Science - (Jan 2014 - Jan 2018)
- DTU - Technical University of Denmark - Computer Science - (Jan 2017 - Jan 2017): Copenhagen Study Abroad Program (1 Semester)
- Caltech - Bachelor’s Degree, Computer Science - (Jan 2014 - Dec 2018): Hacktech
- DTU - Technical University of Denmark - Computer Science - (Jan 2017 - Dec 2017)

## Sources
- https://www.linkedin.com/in/joonheelee
- https://www.linkedin.com/in/joonheelee?miniProfileUrn=urn%3Ali%3Afsd_profile%3AACoAABafDFEBMYVr-Che-ktCu6-VZs_HWOaxn5g
- https://cognition.com/blog/making-fable-cheaper-than-opus
- https://www.youtube.com/watch?v=QHBjufYK8TA
- https://www.youtube.com/watch?v=ZQ3EeU-hYSA
- https://cognition.com/blog/frontier-code-1.1
- https://cognition.com/blog/devin-fusion
- https://www.linkedin.com/posts/csalexiuk_going-to-go-live-with-joon-hee-lee-from-cognition-activity-7497754597957046272-BDJY
- https://poe.com/joon
- https://www.getprog.ai/profile/joon_lee_9364360
- https://www.linkedin.com/posts/joonheelee_poe-for-desktop-activity-7037607352040136704-hv8J
- https://www.linkedin.com/posts/joonheelee_really-excited-to-launch-this-you-can-now-activity-7300212230216671233-3X95
- https://fc.bnext.com.tw/articles/view/4816
- https://www.linkedin.com/in/andrew-coleman-819439?miniProfileUrn=urn%3Ali%3Afsd_profile%3AACoAAAAQZFUBn8yFY-anNdZIPL5fi00cGWFFvUg
- https://www.linkedin.com/company/cognition-ai-labs/posts
- https://www.linkedin.com/in/waldenyan?miniProfileUrn=urn%3Ali%3Afsd_profile%3AACoAAC1PHewBBkvpJyr7GRyFYLzgX5vJA7VZB00
- https://www.linkedin.com/showcase/poe-platform/posts
- https://www.linkedin.com/posts/joonheelee_devin-fusion-was-the-first-major-project-activity-7482555849337372672-4uiD
- https://www.linkedin.com/posts/joonheelee_introducing-swe-17-the-most-capable-model-activity-7480679840589717504-BiIl


Researched with Autumn (https://www.autumn.ai) from public sources. Updated 2026-11-04. Profile: https://www.autumn.ai/resources/cognition/people/joon-hee-lee · Everyone at Cognition: https://www.autumn.ai/resources/cognition/people