Stellar is adding post-quantum signatures. Stellar itself is not going post-quantum.
Bell, Protocol 30, lets smart contracts verify ML-DSA, a NIST post-quantum standard, so a contract account can require a quantum-safe signature before it spends. Regular network transactions stay on Ed25519. SDF's own FAQ asks "Does Bell make Stellar post-quantum?" and answers "No."
Also included: new W addresses so one smart account can serve many customers, and a millisecond ledger clock that doesn't make blocks faster yet, just makes faster possible later.
Testnet vote Nov. 3, mainnet Nov. 23. As of Sunday, Stellar Atlas showed 0 of 91 validators advertising the new version.
Quantum-proof lock on the safe deposit box. Front door still takes the old key.
Source: Stellar Development Foundation: Introducing Bell, Protocol 30