Hi @oliviertassinari and @mbrookes,
I just gave the extended fab a run. Thanks for adding it. However, I believe that the extended fab solution can be improved to enable the following behavior, part of the new Google guideline.
The following demo is based on the existing example on material-ui.com but modified on the fly from dev tools:

Here's my observations from the current implementation:
hideLabel or hideText.Thoughts?
The specification https://material.io/design/components/buttons-floating-action-button.html#extended-fab.
I start to believe that we should move the floating action button into it's own component. This would allow to grow the number of feature without arming the canonical use case of the button. It would also allow to pick a different API tradeoff.
Good ideas @oliviertassinari . I'd just keep in mind that one type could morph to another. Today, it's Fab to Extended Fab. Tomorrow, it could be floating to non-floating. Changing apis on the fly could prevent such transitions. But then again, I'm not 100% sure what you have in mind.
@simoami The height of the extended fab is per the spec. If you look carefully at the transformation examples, it changes height between the extended and standard fab. (However the speed dial example keeps the extended height of 48px for both.)
@mbrookes Good observation. I think the speed dial is a separate feature we don't need to worry much about, since you control the css of the inner components.
The measurements are on the page as well: https://material.io/design/components/buttons-floating-action-button.html#specs

Yup, I think you'll find the extended FAB meets those dimension.
@simoami Do you have the above example in a code pen or similar? I would love to see how you are making the smooth transition between showing and hiding text. Thanks!
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Sorry, but could someone explain the interaction? From the image it looks like clicking triggers the normal click event but is to a drag to the right that reveals the label?
@anthonydillon I believe in @simoami's example, the Fab variant is being controlled programatically.
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I start to believe that we should move the floating action button into it's own component. This would allow to grow the number of feature without arming the canonical use case of the button. It would also allow to pick a different API tradeoff.