# TBB and 2.21

**URL:** <https://discourse.mc-stan.org/t/tbb-and-2-21/11179>\
**Category:** Developers\
**Created:** [September 30, 2019, 9:29am UTC](https://discourse.mc-stan.org/t/tbb-and-2-21/11179 "2019-09-30T09:29:02Z")\
**Posts on this page:** 1\
**Showing post:** 21

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**Author:** ![syclik](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/syclik/32/6_2.png) [@syclik](https://discourse.mc-stan.org/u/syclik)\
**Post date:** [October 17, 2019, 1:32am UTC](https://discourse.mc-stan.org/t/tbb-and-2-21/11179/21 "2019-10-17T01:32:54Z")

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> [@wds15](#):
>
> Just to make sure this doesn’t pass by without notice: As the TBB is now fully integrated into Stan-math, this turns Stan-math into a **non** header-only library! The TBB must be linked against in any circumstances (with/without threading). Doing so allows for the cleanest design.

@wds15, thanks for tagging me. I think this means we bump the major version. I think @seantalts is supposed to make the call, but after we make a suggestion.

What do you think? This seems like it changes what we used to be as the Math library. We’re no longer a header-only with optional link library for certain things. And… we have a new library dependency. If you’re using Math and are GPLv2 and distribute the code, then you will be in violation after this new release.

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