Felix Rieseberg

Felix Rieseberg is an engineer at Anthropic and an Electron co-maintainer. He has led engineering for Claude.ai, Cowork and Code Desktop. His Cowork work brings Claude Code’s task-execution capabilities to people who do not work in a terminal, with a virtual machine that gives the agent room to install tools and run scripts while constraining its access.[2][1]

Rieseberg and his colleagues noticed users putting Claude Code to work on expenses, receipts and knowledge-base organization. In his March 17, 2026 interview, he described Cowork as a way to bring those capabilities to people unfamiliar with terminal tools. His team chose to build on Claude Code rather than recreate its underlying agent harness.[1]

Rieseberg qualified the widely discussed ten-day build: Cowork combined existing components and internal prototypes, some stretching back roughly a year and a half. The short development period did not represent creation of the whole stack from scratch. He also argued that cheaper execution changes how teams choose products: “I really strongly believe now you just build all of them and try them out with a small focus group”.[1]

Giving Claude its own computer was a consequential design choice. In March 2026, Cowork ran Claude Code in a lightweight Linux virtual machine where it could install tools such as Python and Node.js. Network ingress and egress controls, together with filesystem boundaries, constrained what it could access. Rieseberg explained that this also spared nontechnical users questions about tool installation whose security implications they might struggle to assess. He acknowledged real costs, including slower startup than running directly on the host computer.[1]

His team adapted Cowork through knowledge-work evaluations, system-prompt changes and integration with Claude in Chrome. Rieseberg described evaluations that examine both chat responses and generated files. For longer, more ambiguous assignments, the team encouraged heavier use of planning and clarification tools so the agent would establish what the user wanted before spending hours on the wrong task. Those planning capabilities also existed in Claude Code.[1]

Rieseberg’s own crash-report workflow illustrated the move toward broader delegation. He recalled initially choosing individual reports and asking Claude to fix them, then asking Cowork to read the bug list, distinguish fixable application bugs from operating-system crashes, and write a Markdown prompt for each selected bug. Cowork then launched Claude Code remote tasks for the repairs. He explicitly distinguished this arrangement from Claude Code’s native subagent functionality: the remote tasks could continue while he went to his next meeting.[1]

Rieseberg argues that Silicon Valley undervalues the local computer. An assistant, in his view, needs access to the tools its user already has; repeatedly granting and maintaining permissions across cloud services creates friction. He favors integrating with existing applications and browsers. He also leaves open whether people would want their entire working environment copied into the cloud, describing questions of personal data as involving intimacy as well as privacy.[1]

He values skills as ordinary text files that explain a workflow to the model. Their lack of rigid structure makes them easy to write and move between products; Claude Code and Cowork share a plugin format for distributing them. Rieseberg credits Barry and the team with the work that became skills, recalling a prototype connected to a data warehouse through written instructions rather than a custom tool. He considers the separation of reusable instructions from private preferences an unresolved portability problem.[1]

For Rieseberg, useful automation requires users to delegate and walk away. Approving every command defeats that purpose, and users may lack the expertise—or inclination—to inspect generated scripts. He advocates layered safeguards that let agents act within controlled boundaries. His ambition for Cowork, expressed in March 2026, was to let users hand over increasingly large tasks for longer periods with fewer interventions.[1]

Rieseberg also expresses concern about the work this automation displaces: tasks senior workers find tedious often provide employment and experience for junior staff. He does not claim expertise in forecasting effects across legal, finance or marketing roles. Drawing on engineering teams he has worked with, he praises graduates with substantial internship and shipping experience and asks how early-career learning can survive when junior work is compressed.[1]

Before Anthropic, Rieseberg worked on desktop frameworks, application infrastructure and developer tooling. That earlier work supplies concrete context for his views on controlling the environment in which software runs.[2][3][1]

Rieseberg worked in Microsoft startup developer evangelism from 2011 to 2014, first in Berlin and then in the San Francisco Bay Area. As an Open Source Engineer from 2014 to 2016, he built tools including windows-build-tools and npm-windows-upgrade. From 2016 to 2021, he was a Senior Staff Engineer and Engineering Manager at Slack, supporting Electron development and Slack’s macOS, Windows and Linux desktop applications. He subsequently led Stripe’s Payments Integration Experience team from 2021 to 2023 and Notion’s Web Infrastructure and Desktop App teams from 2023 to 2025.[2]

In a January 2017 article coauthored with Anaïs Betts, Rieseberg explained Slack’s partnership with Microsoft to bring Electron applications into the Windows Store and connect them to Windows Runtime APIs. NodeRT generated native Node addons from WinRT metadata, exposing APIs to JavaScript. Store packaging supplied the package identity required by some APIs. Their account described collective contributions to electron-windows-store, which automated packaging and signing, and electron-windows-notifications for rich Windows notifications.[4]

In his January 2025 Electron essay, Rieseberg argued that bundling a rendering engine gives application developers control over stability, security and reliability independently of operating-system WebViews. He recalled Slack’s early use of MacGap and users finding its embedded WebView slower than Chrome. That was his retrospective assessment, rather than a universal performance result. He also emphasized that Electron can combine a web interface with native C++, Objective-C or Rust code, including native UI components and intensive processing.[3]

His playful windows95 project, announced in August 2018, packages Windows 95 in an Electron application for macOS, Windows and Linux. Rieseberg recalled building the wrapper in one night as a joke for Slack colleagues during a debate about JavaScript performance. He did not write the processor emulator: the repository credits the underlying v86 work to Fabian Hemmer, also known as Copy, and his contributors.[5][1]