Spire Serpent — ruling 1

Spire Serpent still has defender if you control three or more artifacts, although it will be able to attack.

Spire Serpent — ruling 2

If Spire Serpent has been declared as an attacker, and you stop controlling three or more artifacts later in combat, Spire Serpent continues being an attacking creature until combat ends.

Spire Serpent : règles, fonctionnement et interactions (MTG)

Spire Serpent is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Defender Metalcraft — As long as you control three or more artifacts, this creature gets +2/+2 and can attack as though it didn't have defender.

How it works : Spire Serpent

Original English text — Wizards of the Coast / Scryfall

#1June 1, 2011· Wizards of the Coast
Spire Serpent still has defender if you control three or more artifacts, although it will be able to attack.
No other card is named in this ruling.
#2June 1, 2011· Wizards of the Coast
If Spire Serpent has been declared as an attacker, and you stop controlling three or more artifacts later in combat, Spire Serpent continues being an attacking creature until combat ends.
No other card is named in this ruling.