[cmovq]

Can someone using modules chime in on whether they’ve seen build times improve?

[nickelpro]

import std; is an order of magnitude faster than using the STL individually, if that's evidence enough for you. It's faster than #include <iostream> alone.

Chuanqi says "The data I have obtained from practice ranges from 25% to 45%, excluding the build time of third-party libraries, including the standard library."[1]

[1]: https://chuanqixu9.github.io/c++/2025/08/14/C++20-Modules.en...

[luke5441]

Yeah, but now compare this to pre-compiled headers. Maybe we should be happy with getting a standard way to have pre-compiled std headers, but now my build has a "scanning" phase which takes up some time.

[direwolf20]

Modules are a lot like precompiled headers, but done properly and not as a hack.

[nickelpro]

The OP does this and measures ~1.2x improvement over PCH.

[vitaut]

We did see build time improvements from deploying modules at Meta.