The small brother CELMM1.TG from the Osram Oslon Boost HX is available at "RS":https://uk.rs-online.com/web/p/leds/1973281/.
Too bad its a the lowest flux bin S3=375lm @ 1500mA
Vf is 3 - 3.25V @ 1500mA
Additionally a new MCPCB is necessary:
400lm at that size is pretty close in intensity to the 900lm of a 1mm2 white flat with twice the area.
With overdriving this LED might be able to beat the 1mm white flat…
1.5x output would be 560lm, so like 25% more intensity than the white flat.
The question is can we get to 1.5x with such a small thermal pad.
Someone needs to do some tests!
Also the bin is S3SA which means it could be anywhere from S3 to SA, no way to know.
It could be higher than S3.
Lumintop Micro GT would be a nice host for this tiny LED !
I have a KW CULNM1-TG (4040 1mm2 White Flat) in my Micro GT and I would not want to swap it for an even smaller led, unless narrow beams are your way of fun. (Ok, narrow beams are fun :party: )
Micro GT runs the 1mm just fine and with the new Shockli and Vapcell high current 14500, they can even push the 2mm version to the max.
This emitter would be perfect for the GT Nano!
My Micro GT does 100kCd with a Black Flat… No need for a smaller LED indeed 
I’d be looking at this for smaller lights like S2+ and AA/AAAs if it wasn’t for that footprint, no chance of bodging it onto any MCPCBs i have.