# Developers

**URL:** https://discourse.mc-stan.org/c/stan-dev/10.md

[Latest](https://discourse.mc-stan.org/latest.md) · [Categories](https://discourse.mc-stan.org/categories.md) · [Tags](https://discourse.mc-stan.org/tags.md)

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## [About the Developers category](https://discourse.mc-stan.org/t/about-the-developers-category/22)

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**Author:** [@syclik](https://discourse.mc-stan.org/u/syclik)\
**Replies:** 0\
**Last updated:** [August 14, 2016, 10:04pm UTC](https://discourse.mc-stan.org/t/about-the-developers-category/22 "2016-08-14T22:04:10Z")

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This category is for discussion relevant to the development of Stan. This includes the present and future of the core Stan code and its interfaces.

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## [Stan, stanr, and brms running client-side in the browser via webR](https://discourse.mc-stan.org/t/stan-stanr-and-brms-running-client-side-in-the-browser-via-webr/41549)

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**Author:** [@StaffanBetner](https://discourse.mc-stan.org/u/StaffanBetner)\
**Replies:** 6\
**Last updated:** [September 22, 2026, 7:57am UTC](https://discourse.mc-stan.org/t/stan-stanr-and-brms-running-client-side-in-the-browser-via-webr/41549 "2026-09-22T07:57:42Z")

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Hi all, I’ve been experimenting with running Stan inside webR and wanted to share a working proof-of-concept. Thanks to @seantalts’ work on stanli (the Stan interpreter/runtime) and @andrjohns’ work on stanr and his st…

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## [Comparing stan backend to Julia / native cpp (ctsem, continuous time nonlinear state space modelling)](https://discourse.mc-stan.org/t/comparing-stan-backend-to-julia-native-cpp-ctsem-continuous-time-nonlinear-state-space-modelling/41545)

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**Author:** [@Charles\_Driver](https://discourse.mc-stan.org/u/Charles_Driver)\
**Replies:** 16\
**Last updated:** [September 22, 2026, 7:31am UTC](https://discourse.mc-stan.org/t/comparing-stan-backend-to-julia-native-cpp-ctsem-continuous-time-nonlinear-state-space-modelling/41545 "2026-09-22T07:31:53Z")

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Just thought it might interest some here – I’m migrating the ctsem software GitHub - cdriveraus/ctsem: Hierarchical continuous time state space modelling · GitHub (now with GUI for anyone really curious! GitHub - cdriver…

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## [Stanwasm: a browser-first Stan subset with per-model wasm codegen — looking for feedbackd](https://discourse.mc-stan.org/t/stanwasm-a-browser-first-stan-subset-with-per-model-wasm-codegen-looking-for-feedbackd/41568)

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**Author:** [@habakan](https://discourse.mc-stan.org/u/habakan)\
**Replies:** 4\
**Last updated:** [September 9, 2026, 1:19am UTC](https://discourse.mc-stan.org/t/stanwasm-a-browser-first-stan-subset-with-per-model-wasm-codegen-looking-for-feedbackd/41568 "2026-09-09T01:19:31Z")

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I’ve been independently building stanwasm, an implementation of a subset of the Stan language that parses, compiles and samples models entirely in the browser. It is an independent implementation rather than a port: it…

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## [Planning the 2.40 release](https://discourse.mc-stan.org/t/planning-the-2-40-release/41502)

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**Author:** [@WardBrian](https://discourse.mc-stan.org/u/WardBrian)\
**Replies:** 7\
**Last updated:** [September 8, 2026, 8:56pm UTC](https://discourse.mc-stan.org/t/planning-the-2-40-release/41502 "2026-09-08T20:56:16Z")

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It’s that time again! We’re coming up on 4 months post-2.39 release (May 19th). I’d like to propose the following dates for the 2.40 release: Feature freeze on Tuesday, September 8th 2026 Release on Tuesday, September…

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## [Big Collection of Stan Ecosystem PRs](https://discourse.mc-stan.org/t/big-collection-of-stan-ecosystem-prs/41544)

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**Author:** [@scholz](https://discourse.mc-stan.org/u/scholz)\
**Replies:** 11\
**Last updated:** [September 8, 2026, 8:40pm UTC](https://discourse.mc-stan.org/t/big-collection-of-stan-ecosystem-prs/41544 "2026-09-08T20:40:40Z")

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Bob made me do it! After watching the walnutpie video by @Bob\_Carpenter I decided to spend some time with walnutpie. When I first saw it announced on Andrew’s Blog I commented that trying out muon as an alternative to a…

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## [On the usage of Pystan with other sampling libraries in python](https://discourse.mc-stan.org/t/on-the-usage-of-pystan-with-other-sampling-libraries-in-python/41539)

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**Author:** [@dgsharp](https://discourse.mc-stan.org/u/dgsharp)\
**Replies:** 6\
**Last updated:** [August 21, 2026, 6:48pm UTC](https://discourse.mc-stan.org/t/on-the-usage-of-pystan-with-other-sampling-libraries-in-python/41539 "2026-08-21T18:48:26Z")

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Hi! I was at StanCon this week and really appreciated all of the discourse and presentations. One thing that came up in a conversation with @WardBrian was the ability to benchmark other tools’ samplers with Stan-based mo…

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## [Subtree acceptance probablity in base\_nuts.hpp:166](https://discourse.mc-stan.org/t/subtree-acceptance-probablity-in-base-nuts-hpp-166/41303)

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**Author:** [@andre.pfeuffer](https://discourse.mc-stan.org/u/andre.pfeuffer)\
**Replies:** 5\
**Last updated:** [June 5, 2026, 7:40pm UTC](https://discourse.mc-stan.org/t/subtree-acceptance-probablity-in-base-nuts-hpp-166/41303 "2026-06-05T19:40:26Z")

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The relevant section in 2.39.0 base\_nuts.hpp:163-172: if (log\_sum\_weight\_subtree \> log\_sum\_weight) { z\_sample = z\_propose; // always accept } else { double accept\_prob = std…

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## [Formatting large JSON academic metadata for meta-analysis priors in Stan](https://discourse.mc-stan.org/t/formatting-large-json-academic-metadata-for-meta-analysis-priors-in-stan/41326)

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**Author:** [@Stream\_On](https://discourse.mc-stan.org/u/Stream_On)\
**Replies:** 1\
**Last updated:** [June 5, 2026, 6:56pm UTC](https://discourse.mc-stan.org/t/formatting-large-json-academic-metadata-for-meta-analysis-priors-in-stan/41326 "2026-06-05T18:56:09Z")

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Hi everyone, I am currently working on a hierarchical Bayesian meta-analysis model in Stan, where I need to synthesize effect sizes from a large corpus of existing academic literature. A major practical hurdle is build…

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## [What is the correct way to request a code review for contributions to math?](https://discourse.mc-stan.org/t/what-is-the-correct-way-to-request-a-code-review-for-contributions-to-math/41246)

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**Author:** [@jachymb](https://discourse.mc-stan.org/u/jachymb)\
**Replies:** 3\
**Last updated:** [May 18, 2026, 9:05pm UTC](https://discourse.mc-stan.org/t/what-is-the-correct-way-to-request-a-code-review-for-contributions-to-math/41246 "2026-05-18T21:05:56Z")

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I tried to implement some stuff into Stan math that I was missing and made a PR but I’m unsure how to get someone to review it. Should I simply wait until someone looks at it, or is there another protocol to ask for a re…

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## [Using JAX as an AD backend](https://discourse.mc-stan.org/t/using-jax-as-an-ad-backend/38979)

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**Author:** [@spinkney](https://discourse.mc-stan.org/u/spinkney)\
**Replies:** 9\
**Last updated:** [May 15, 2026, 3:06pm UTC](https://discourse.mc-stan.org/t/using-jax-as-an-ad-backend/38979 "2026-05-15T15:06:13Z")

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I’m looking through the JAX (I’m going to go lowercase jax for the rest bc I’m on mobile) docs about the foreign function interface (ffi) and I see this about cuda GPU Foreign function interface (FFI) — JAX documentation.…

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## [Project Idea: Benchmarking Framework for Individual Functions in stan/math](https://discourse.mc-stan.org/t/project-idea-benchmarking-framework-for-individual-functions-in-stan-math/41233)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 0\
**Last updated:** [May 15, 2026, 12:07pm UTC](https://discourse.mc-stan.org/t/project-idea-benchmarking-framework-for-individual-functions-in-stan-math/41233 "2026-05-15T12:07:13Z")

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In MCMC algorithms, many functions at a lower level are called repeatedly. The way one implements something can largely affect runtime, in particular in C++ since typing matters (creating unnecessary copies, others might…

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## [C++, Multithreading, Benchmarking](https://discourse.mc-stan.org/t/c-multithreading-benchmarking/41118)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 0\
**Last updated:** [May 9, 2026, 11:32am UTC](https://discourse.mc-stan.org/t/c-multithreading-benchmarking/41118 "2026-05-09T11:32:24Z")

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If any other C++ devs aren’t following the github, here’s the discussion we’re having. If steve’s not available, any input is appreciated. Again, benchmarks were done just on executing stan/math/prim/fun/exp.hpp and the…

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## [Compiling Flatiron Server Tests Locally](https://discourse.mc-stan.org/t/compiling-flatiron-server-tests-locally/41111)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 2\
**Last updated:** [May 8, 2026, 3:29pm UTC](https://discourse.mc-stan.org/t/compiling-flatiron-server-tests-locally/41111 "2026-05-08T15:29:16Z")

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Hi, I’ve switched my compiler to gcc 9, which looks like what’s used on the Flatiron servers, but I’m re-running tests locally, and I’m not getting the same errors when running tests or compiling. What local compiler o…

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## [Different Compiler, WSL](https://discourse.mc-stan.org/t/different-compiler-wsl/41113)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 1\
**Last updated:** [May 8, 2026, 2:33pm UTC](https://discourse.mc-stan.org/t/different-compiler-wsl/41113 "2026-05-08T14:33:38Z")

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I’m trying to use a different compiler, gcc9, and I’m using WSL on windows. I have my local/make set to: TBB\_CXX\_TYPE=gcc CXX=/home/andre/stan-dev/misc/9 STAN\_THREADS=true I’m still getting “permission denied”. I’ve t…

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## [Good Starter Project to get Involved: Adding Models to Posteriordb](https://discourse.mc-stan.org/t/good-starter-project-to-get-involved-adding-models-to-posteriordb/41096)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 0\
**Last updated:** [May 2, 2026, 1:50am UTC](https://discourse.mc-stan.org/t/good-starter-project-to-get-involved-adding-models-to-posteriordb/41096 "2026-05-02T01:50:43Z")

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For anyone who wants to get started, I’ve opened a PR on posteriordb that contains a bunch of models that have already been tested thoroughly, as they were used to evaluate whether covariance functions developed in C++ w…

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## [Benchmarking Multithreading for stan:math::exp using tbb, Proof of Concept (POC)](https://discourse.mc-stan.org/t/benchmarking-multithreading-for-stan-exp-using-tbb-proof-of-concept-poc/41074)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 3\
**Last updated:** [April 30, 2026, 3:12pm UTC](https://discourse.mc-stan.org/t/benchmarking-multithreading-for-stan-exp-using-tbb-proof-of-concept-poc/41074 "2026-04-30T15:12:31Z")

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I think I made this faster. So I’m scaling number of threads. I did a quick grep through the stan/math, and it doesn’t look like anyone’s actually using TBB for multithreading yet. I used: Here are some results, after…

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## [C+++ Promoting Datatypes with Forward, Apply](https://discourse.mc-stan.org/t/c-promoting-datatypes-with-forward-apply/41070)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 1\
**Last updated:** [April 25, 2026, 5:52pm UTC](https://discourse.mc-stan.org/t/c-promoting-datatypes-with-forward-apply/41070 "2026-04-25T17:52:54Z")

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So I’m staring at this (stan/math/prim/fun/exp.hpp), good to just ask. I guess in this block of code we’re “forwarding” the datatype of x to v, and then applying (like a lambda?) this to v: return apply\_vector\_unary\<C…

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## [Scaling the multithreading](https://discourse.mc-stan.org/t/scaling-the-multithreading/41019)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 5\
**Last updated:** [April 21, 2026, 8:32pm UTC](https://discourse.mc-stan.org/t/scaling-the-multithreading/41019 "2026-04-21T20:32:22Z")

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So I think Sebastian implemented a TBB multithreaded version of base\_nuts.cpp, I’m assuming it’s implemented correctly, but I want to see how it scales on the pre-existing models. It’s been a while, but I remember openin…

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## [What's Parallelizable in the Math Library](https://discourse.mc-stan.org/t/whats-parallelizable-in-the-math-library/41062)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 1\
**Last updated:** [April 21, 2026, 7:50pm UTC](https://discourse.mc-stan.org/t/whats-parallelizable-in-the-math-library/41062 "2026-04-21T19:50:15Z")

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Hello, After a first pass/skim through the math library, here’s some quick notes. Any comments are appreciated, but I’m mostly talking to myself. I’m talking about multithreading, and not just running a different proces…

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## [Planning the 2.39 release](https://discourse.mc-stan.org/t/planning-the-2-39-release/41044)

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**Author:** [@WardBrian](https://discourse.mc-stan.org/u/WardBrian)\
**Replies:** 2\
**Last updated:** [April 13, 2026, 6:55pm UTC](https://discourse.mc-stan.org/t/planning-the-2-39-release/41044 "2026-04-13T18:55:13Z")

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It’s that time again! We’re coming up on 4 months post-2.38 release (January 13th). I’d like to propose the following dates for the 2.39 release: Feature freeze on Monday, May 11th 2026 Release on Monday, May 18th 202…

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## [Performance tests cloning recursively](https://discourse.mc-stan.org/t/performance-tests-cloning-recursively/41025)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 1\
**Last updated:** [April 9, 2026, 7:25pm UTC](https://discourse.mc-stan.org/t/performance-tests-cloning-recursively/41025 "2026-04-09T19:25:46Z")

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This could be an issue with WSL, I was trying to clone earlier, and getting missing directories and trying to build the stan stack manually. Now it seems to be working. But when I’m cloning performance tests, it’s not gi…

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## [Performance Tests - Windows](https://discourse.mc-stan.org/t/performance-tests-windows/41034)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 1\
**Last updated:** [April 9, 2026, 7:17pm UTC](https://discourse.mc-stan.org/t/performance-tests-windows/41034 "2026-04-09T19:17:44Z")

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I’m not having any trouble with the math library, or cmdstan in windows using WSL, but I’m trying to run performance tests and getting issues. Cannot execute, required file not found? Not sure, I’ll come back to it but u…

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## [Proof of concept: Binary output format for cmdstan](https://discourse.mc-stan.org/t/proof-of-concept-binary-output-format-for-cmdstan/40846)

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**Author:** [@scholz](https://discourse.mc-stan.org/u/scholz)\
**Replies:** 74\
**Last updated:** [April 8, 2026, 1:33pm UTC](https://discourse.mc-stan.org/t/proof-of-concept-binary-output-format-for-cmdstan/40846 "2026-04-08T13:33:47Z")

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Jonah made me do it Report: CmdStan Binary Output Format Fork with code: GitHub - sims1253/cmdstan: CmdStan, the command line interface to Stan

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## [Cloning Stan in MINGW64 or WSL](https://discourse.mc-stan.org/t/cloning-stan-in-mingw64-or-wsl/41033)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 2\
**Last updated:** [April 7, 2026, 1:16pm UTC](https://discourse.mc-stan.org/t/cloning-stan-in-mingw64-or-wsl/41033 "2026-04-07T13:16:59Z")

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I had this working a while ago, I’m cloning cmdstan and I’m getting missing directories. Last time I was active with stan, all of the stansummary files were in cmdstan/bin/, now from the git repo it looks like they’re i…

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## [Parallelism in Stan](https://discourse.mc-stan.org/t/parallelism-in-stan/288)

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**Author:** [@wds15](https://discourse.mc-stan.org/u/wds15)\
**Replies:** 10\
**Last updated:** [March 31, 2026, 3:25pm UTC](https://discourse.mc-stan.org/t/parallelism-in-stan/288 "2026-03-31T15:25:54Z")

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Hi! As discussed recently in our meetings, I started a wiki on parallelism in Stan here: The motivating example case are hierarchical ODEs, but I am sure that other areas of Stan can benefit from the proposed appr…

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## [Parallel dynamic HMC merits](https://discourse.mc-stan.org/t/parallel-dynamic-hmc-merits/10895)

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**Author:** [@wds15](https://discourse.mc-stan.org/u/wds15)\
**Replies:** 41\
**Last updated:** [March 27, 2026, 4:18pm UTC](https://discourse.mc-stan.org/t/parallel-dynamic-hmc-merits/10895 "2026-03-27T16:18:49Z")

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Hi there! I have been thinking about parallelizing our dynamic HMC sampler. The obvious strategy to do that is to pre-sample all the fwd and bck turns up to the maximal treedepth then expand the fwd and back trajector…

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## [2-factor authentication now required in Stan repos](https://discourse.mc-stan.org/t/2-factor-authentication-now-required-in-stan-repos/41008)

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**Author:** [@avehtari](https://discourse.mc-stan.org/u/avehtari)\
**Replies:** 0\
**Last updated:** [March 26, 2026, 4:41pm UTC](https://discourse.mc-stan.org/t/2-factor-authentication-now-required-in-stan-repos/41008 "2026-03-26T16:41:13Z")

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SGB decided that due to security risks in using only password and increasing amount of malicious attacks, Stan repos now require that github accounts enbale 2-factor authentication. This is not limiting access, as you ca…

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## [Possible Projects? Looking for something to do](https://discourse.mc-stan.org/t/possible-projects-looking-for-something-to-do/41000)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 0\
**Last updated:** [March 25, 2026, 4:34am UTC](https://discourse.mc-stan.org/t/possible-projects-looking-for-something-to-do/41000 "2026-03-25T04:34:03Z")

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hey, I’m looking to get my hands dirty and keep my chops together. I like to do quantitative stuff. There was some talk about parallelization. I left off with VI diagnostics, but not sure if this is relevant anymore. A…

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## [Claude Generating Slop Gaussian Process Regression Models](https://discourse.mc-stan.org/t/claude-generating-slop-gaussian-process-regression-models/40999)

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**Author:** [@drezap](https://discourse.mc-stan.org/u/drezap)\
**Replies:** 0\
**Last updated:** [March 25, 2026, 4:22am UTC](https://discourse.mc-stan.org/t/claude-generating-slop-gaussian-process-regression-models/40999 "2026-03-25T04:22:51Z")

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See Claude generating slop “Gaussian process regression models”

[Next page](https://discourse.mc-stan.org/c/stan-dev/10.md?page=1)