I'm assuming you're referring to the
marketing name, not the
codename. The marketing name for macOS 26 is Tahoe, but the codename was "Cheer."
In fact, only 4 OS versions in the OSX era have actually used their codenames as a full release marketing name (Cheetah, Puma, Jaguar and Snow Leopard).
Here's the list of the marketing names and their respective internal codenames:
- Mac OS X: Cyan, Siam
- Mac OS X Developer Preview 3 – Bunsen
- Mac OS X Developer Preview 4 — Gonzo
- Mac OS X Public Beta — Kodiak
- Mac OS X Public Release 1 — Hera
- Mac OS X Public Release 2 — Beaker
- Mac OS X 10.0 — Cheetah
- Mac OS X 10.1 — Puma
- Mac OS X 10.2.1 — Red
- Mac OS X 10.2.2 — Blue
- Mac OS X 10.2.3 — Green
- Mac OS X 10.2.4 — Pink
- Mac OS X 10.2.7 — Blackrider, Smeagol
- Mac OS X 10.3 Panther — Pinot
- Mac OS X 10.4 Tiger — Merlot
- Mac OS X 10.4.1 Tiger — Atlanta
- Mac OS X 10.4.4 Tiger (Intel version) — Chardonnay
- Mac OS X 10.5 Leopard — Chablis
- Mac OS X 10.6 – Snow Leopard
- Mac OS X 10.7 Lion — Barolo
- OS X 10.8 Mountain Lion — Zinfandel
- OS X 10.9 Mavericks — Cabernet
- OS X 10.10 Yosemite — Syrah
- OS X 10.11 El Capitan — Gala
- macOS 10.12 Sierra — Fuji
- macOS 10.13 High Sierra — Lobo
- macOS 10.14 Mojave — Liberty
- macOS 10.15 Catalina — Jazz
- macOS 11.0 Big Sur — GoldenGate
- macOS 12.0 Monterey — Star
- macOS 13.0 Ventura — Rome
- macOS 14.0 Sonoma — Sunburst
- macOS 15.0 Sequoia — Glow
- macOS 26.0 Tahoe — Cheer
*List copy/pasted from here for expediency... if you're interested, check out the codenames of Apple Watch way down at the bottom.