For the first time, I demonstrate that the three Pyramids of Giza and the Great Sphinx are the constellation Cygnus built in stone — and I prove it with numbers anyone can verify. Every dimension of the Giza plateau — the height of the Great Pyramid, the three bases, the slope angle, the King's Chamber, the Grand Gallery, and even the distances between structures — can be calculated from just 3 measurements of the Sphinx and 2 angles from the constellation Cygnus. Mean error: 0.15%. Maximum error: 0.54%. The key discovery: Cygnus hides a 4D hypercube (tesseract) in its own geometry. Its angular modules form a Pythagorean cascade that climbs from 2D to 4D, are simultaneously a Fibonacci sequence and a golden ratio progression, and its borders sum to exactly 90°. The probability of all this being coincidence is less than 1 in 3 million. No terrestrial measurement is needed to prove the tesseract — only star positions. The Sphinx is the missing piece. Its body (72.55 m) is the only value that closes the 4D geometry and maintains the golden ratio. Without the Sphinx, Cygnus has 3 dimensions. With it, 4. The Sphinx doesn't represent Cygnus — it completes it. The tesseract was in the sky long before any civilization. Someone found it. And built it in stone. This entire investigation began on February 26, 2025, when I lay inside the granite sarcophagus of the King's Chamber in the Great Pyramid — on the exact day of the heliacal rising of Cygnus and a rare alignment of 7 planets visible to the naked eye. What followed is in this paper and in the book. Full investigation in the book: 'The Hidden Code of Cygnus' (O Código Oculto de Cygnus), Clube de Autores, 2026. Contact: thecygnuscode@gmail.com | Instagram: @lucascygnus | YouTube: youtube.com/@cygnuscodebr Book: https://clubedeautores.com.br/livro/o-codigo-oculto-de-cygnus-2