I bought this golden rat tail cactus about a m…

I bought this golden rat tail cactus about a month or two ago, and recently the ends have become elongated. Is this new growth or is it from lack of light? (I have it right in front of my window)

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It’s possible that it’s both. The bright green end is most definitely new growth, but it’s too soon to tell whether it will fill out like the older part of the cactus or if it will stretch from lack of light. Usually etiolated growth is more yellow or a paler green, though – so that’s a good sign!