Mojo reaches 1.0 with a primarily-additive change policy, while the compiler stays closed

Sources: primary, discussion
Summary: Modular released Mojo 1.0 as part of Modular 26.5 and states that changes during the 1.x timeframe should primarily be additive, while adding that breaking changes may still be made and will be managed the way mature languages such as C++ evolve. The compiler remains closed source, and Modular restates a commitment to open source the Mojo compiler and toolchain in 2026 and to progressively open source more of the language. The release comes under Qualcomm ownership of Modular.
Why it matters: Mojo has been unstable enough that long-term projects were hard to maintain, and 1.0 is the point where Modular asks teams to build on it, with the compiler still unreleased.
Follow-up: Whether the 2026 date for opening the compiler is met, and how breaking changes are handled across the 1.x releases.