Brett Simmers
Member Of Technical Staff at Anthropic
Mountain View, California, United States
Summary
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Rockstar🎓
Top SchoolBrett Simmers is a seasoned back-end software engineer with 14 years of experience building robust, low-level systems at scale, currently a Member of Technical Staff at Anthropic in Mountain View. He spent over a decade at Meta and earlier at VMware, focusing on performance, concurrency, and core platform reliability. An active open-source contributor, Brett has made substantive changes to CPython’s interpreter—improving C APIs, refcounting, and GIL behavior—and hardened Facebook’s Folly C++ library by fixing format-string issues and optimizing core data structures. His work demonstrates deep systems-level expertise across C and C++ and a practical eye for thread safety and correctness that often surfaces in subtle, hard-to-detect bugs. A Carnegie Mellon computer science graduate, he blends academic rigor with production-hardened engineering judgment. Notably, his contributions to two widely used projects reflect both language-runtime insight and large-scale library robustness.
15 years of coding experience
15 years of employment as a software developer
Bachelor of Science - BS, Computer Science, Bachelor of Science - BS, Computer Science at Carnegie Mellon University
Stackoverflow
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Github Skills (20)
c-language10
python10
thread-safety10
capi10
c1110
c1710
optmization10
performance-optimization10
optimisation10
cprogramming-language10
optimization10
data-structure9
algorithm9
algorithms9
data-structures9
Programming languages (5)
Github contributions (5)
facebook/folly
Mar 2013 - Jun 2016
An open-source C++ library developed and used at Facebook.
Role in this project:
Back-end Developer
Back-end DeveloperContributions:8 commits in 3 years 2 months
Contributions summary:Brett primarily contributed to the `folly` library, a C++ library developed and used at Facebook, by focusing on improving its core functionality and robustness. Their work involved fixing potential errors in format string handling, refactoring code, and addressing performance issues. They also made improvements to the underlying data structures of the library. These changes included fixing issues and increasing the reliability of the library's core features.
cpp
python/cpython
Mar 2023 - Nov 2024
The Python programming language
Role in this project:Back-end Developer
Back-end DeveloperContributions:50 reviews, 13 PRs, 102 comments in 1 year 7 months
Contributions summary:Brett primarily contributed to the core Python codebase, focusing on internal C API improvements and thread safety. They implemented new C API functions and added features to the CPython interpreter, specifically related to versioning and handling the Global Interpreter Lock (GIL) in free-threaded builds. Furthermore, the user addressed refcounting issues and improved thread safety in the `_abc` and `_codecs` modules.
programming-languagepython
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