denoland-deno/docs/runtime/stability.md

Stability

As of Deno 1.0.0, the Deno namespace APIs are stable. That means that we will strive to make code working under 1.0.0 continue to work in future versions.

However, not all of Deno's features are ready for production yet. Features which are not ready because they are still in draft phase are locked behind the --unstable command line flag. Passing this flag does a few things:

• It enables the use of unstable APIs during runtime.
• It adds the lib.deno.unstable.d.ts file to the list of TypeScript definitions that are used for typechecking. This includes the output of deno types.

You should be aware that unstable APIs have probably not undergone a security review, are likely to have breaking API changes in the future and are not ready for production.

Furthermore Deno's standard modules (https://deno.land/std/) are not yet stable. We version the standard modules differently from the CLI to reflect this.