I believe that there is a typo in the summon construct spell from Tasha's Cauldron of Everything. The spell is shown as a 4th-level spell in the table at the beginning of the chapter (p. 105) and in the main entry for the summon construct spell (p. 111).
However, the Construct Spirit's stat block lists its HP formula as:
"40 + 15 for each spell level above 3rd" (emphasis mine).
This is odd, because all of the other stat block formulas for all the other summon [X] spells in the book are formatted such that you only add extra HP if the spell is cast at a higher level.
By RAW, based on the given formula, the construct has 55 HP when cast as a 4th-level spell. However, have there been any designer statements or errata indicating that this was unintentional and that the base HP should actually be 40?
Best Answer
The construct spirit's hit points should read "for each spell level above 4th"
I'm leaving the original answer below for historical reasons. The construct spirit stat block was given an update in the December 2021 errata of Tasha' Cauldron that clears things up:
Confirming my original conclusion that the stat block should read:
As written, 55 hitpoints.
As written, the stat block is unambiguous, if a bit odd. The hit points in the statblock says:
So casting at 4th level obviously gives 55 hit points.
There is almost certainly something misprinted here.
I am almost certain this is not intended. Every other summon something spell in Tasha's follows the traditional formula of Nth-level spell and using N+1 in the "At Higher Levels" section.
As MonkeezOnFire pointed out in comments, there are several other places in the book where the spell is referred to as a 4th level spell.
The table at the beginning of the section "Magical Miscellany" lists summon construct as 4th level, and the clockwork soul sorcerer's additional spells table list summon construct together with freedom of movement, also a 4th level spell. Further, the additional wizard spells table lists summon construct as a 4th level spell.
The preponderance of evidence points to the intention being that summon construct is a 4th level spell.
Given this, I believe that statblock should read:
This would give it 40 hit points when cast at 4th level.