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An SDK version is immutable. That is the point: code that shipped last quarter keeps calling exactly what it was built against, while you publish something new alongside it.

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Immutable means immutable

Re-applying identical content to the same version is a no-op — no regeneration, no token rotation. Change the services, operations, auth, injections, or language under an existing version and apply returns app_version_immutable. The fix is always the same: bump the version and publish that.

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When the Registry moves under you

app_version_immutable is about something you changed. Its sibling is about something Fused changed: when the Registry advances the selection schema your published versions were built against, applying an older plan returns app_selection_schema_version_mismatch (HTTP 409), and fused-cli sdk sync refuses a version whose schema is newer than the CLI understands. Neither is a data loss. Re-plan so the selections are rebuilt against the current schema, then apply. If sync is the one complaining, upgrade fused-cli first — it is telling you the Engine is ahead of it.
Do not edit a generated package to impersonate another version. The Engine authorizes the opaque app_id embedded in the package, not a version number the client reports.

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What carries across versions

Because tokens belong to the SDK rather than a version, a new version that expands capability expands what existing tokens can reach. The plan reports which tokens are affected. If two teams must not share capability, give them different SDK names rather than different versions of one. There is no implicit “latest.” Every command that resolves a version wants name@version or a Version ID.

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Inspect what shipped

sdk list shows SDK_ID, stable across versions, and VERSION_ID, identifying one exact immutable version.

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Flags

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sdk download

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sdk list

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sdk openapi

sdk openapi always writes a file and never prints the document to stdout. It needs your ordinary control credential and app.read — an execution token cannot authorize the export.

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Pull the Engine’s state back down

Sync full-mirrors the exact Engine app version your local file declares. Anything the Engine no longer selects is removed locally rather than flagged, and Engine values win on conflict. There is no implicit latest lookup and no sync-time upgrade — change version yourself, then plan and apply it deliberately. One quirk worth expecting: sync freezes the current selection into an explicit sorted operation list, so a service configured with select_all: true does not come back as select_all: true.

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Retiring a version

The CLI has no SDK deprecate or deactivate command. Those lifecycle actions live in the Engine’s App UI and API. If you find yourself reaching for fused-cli sdk deactivate, it does not exist — do not improvise one.

Issue execution tokens

A new version does not need a new token. It may need you to review the old ones.