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⚛️ I updated my reproduction from you-know-when to react 19.0.0-rc.1 and it works great 🚀 stackblitz.com/edit/tanstac... It’s not quite the same as in v18, but definitely the perfect tradeoff:

In 18, the order was: - 🚀 start fetch 1 - 🚀 start fetch 2 - 🌀render fallback Both fetches started at the same time (1ms difference at most), and the fallback rendered afterwards.

In 19-rc.0, we had: - 🚀 start fetch 1 - 🌀 render fallback ... 🐌 - 😭 start fetch 2 with a clear waterfall between fetch 1 and fetch 2, because fetch 2 would only start after fetch 1 had finished.

In 19-rc.1, we get: - 🚀 start fetch 1 - 🌀 render fallback - 🚀 start fetch 2 This combines the best of both worlds thanks to the new pre-warming feature: - ⚡the fallback renders faster - 🙌 we don’t have to wait for fetch 1 to finish before fetch 2 starts.

You can read more about it here: react.dev/blog/2024/04... In my simple example, fetch 2 starts a bit later than in v18 (10-12ms usually), but that’s totally okay and largely irrelevant when async tasks are involved.

It’s also expected because the fallback will be committed before the suspended siblings are rendered. However, if the rest of the tree is large, you might see fallbacks a lot sooner than in v18, which is what the initial change aimed to address.

thanks for ringing the bells on this issue in the first place as well! the whole conversation started from your initial tweets iirc