Linux Github Source Leaks Details Of Intel’s Arc Alchemist 256 EU ‘SOC3’ GPU
One of the expected Alchemist products is in fact a 256-EU SKU, but most enthusiasts expected Intel to make these products by paring down and binning the 512-EU parts. Selling a chip originally intended to be twice as large with half its capacity disabled isn't unheard-of in GPUs, but it would probably mean pretty poor margins for Intel on such a product.
Now it seems likely that those mid-range Alchemist cards might actually be carrying a separate chip altogether. Intel may have found that its yields on the SOC1 (aka DG2-512) chip were better than expected, or some beancounter may have gotten nervous about chopping off half of an SOC1 to make a 256-EU SKU3. Alternatively, SOC3 may not even exist and the entry in the driver could be an artifact of earlier plans.
We could speculate for days on Intel's rationale for such a decision, but ultimately it's likely to come down to profits, one way or the other. In any case, Intel doesn't have much time left before it's expected to reveal the whole Alchemist lineup to the world, so we'll know the whole story sooner than later.