It needs a bigger pot most likely. While many of the cactoid Euphorbias are full-sun plants, they might burn a little in your growing zone if they don't have access to growing room (or if that pot's also in full sun - those roots are aroastin' a bit).

Thanks for the feedback. I transplanted it into a pot that is roughly 4 times the size it originally came in. Teased apart the root ball to separate it into 2. Makes sense that it might be aroastin' since it such a small volume of substrate vs. root structure.

I haven't grown this plant. Are the older spines meant to stay red? I thought the Euphorbias that grow spines like this one start with flexible spines that eventually harden like a rose thorn.

I don't have this specific Euphorbia, but I can tell you that my other Euphorbias do tend to get a bit bleached out in full sun, I keep mine on either east or west side of the house away from overhangs so they get about 5 to 6 hours of direct sun a day. Not sure if this works for everyone else in zone 10, but it seems to do the trick for me.

Thanks polypompholyx. A image search shows many with more brownish spines although a few pics show colored spines to the base. Perhaps less light = more color (but less growth)?

Thanks for the feedback Nicholas! E or W is not an option for me but I will likely rotate them from evening shade to morning shade to 3-4 hours of direct sun, perhaps skipping the direct until Fall weather arrives...if it does.

Keith, if you can, it'd grow best in the ground, but don't put it there until spring.

IME, think of the spines turning brown as natural "corking" for euphorbias. All of the spines will eventually turn brown and the new growth will be red. The sun right now looks perfect for it.

I have grown this plant a lot and yours looks fine... not sure this one can get too much sun seriously... happy the more sun it gets generally (seen far too many getting too little sun pictured on this site).

Thanks everyone!