Turn off the Python Environments experiment #1835

The Python Environments extension rollout reached 100% on July 15, 2026. This meta issue tracks the remaining work required to end the experiment fully, make the extension the sole default environment experience, and remove transitional behavior.

Before turning off the experiment

• Release the stable Python Environments Extension API 2.0: #1837
• Jupyter adopts the Python Environments Extension API: microsoft/vscode-jupyter#17283
• Confirm all first-party consumers use the Python Environments Extension API and no longer depend on the legacy Python extension environment API.
• Remove treatment/control assignment and experiment checks from the Python extension.
• Remove the python.useEnvironmentsExtension opt-in/opt-out setting and its configuration migration paths.
• Remove conditional activation and UI contribution guards tied to python.useEnvironmentsExtension from this extension.
• Remove the superseded environment discovery and management paths from the Python extension.
• Update documentation to reflect that the extension and API are stable: #1836
• Add or update integration coverage to verify the default experience after the experiment and fallback paths are removed.

Completion criteria

• The Python Environments extension is enabled unconditionally for supported Python extension installations.
• Users are no longer assigned to experiment groups and cannot switch back to the legacy experience through python.useEnvironmentsExtension.
• First-party extensions obtain environment information through the Python Environments Extension API.
• No experiment-specific activation, UI, documentation, or tests remain.

The completed rollout history is documented in #581.