Fetch the spec-version transition timeline — the earliest known block at each distinct runtime spec_version, ascending by block_number. A single aggregate over the whole retained blocks window, nothing to filter or paginate. Every block from genesis to head carries a spec_version reading, so coverage_from_block/coverage_from_at and coverage_gaps describe a complete timeline rather than bounding a partial one. Computed live from the first-party blocks tier (#4316/3.1, #9265). The current block (#8702) adds the forward-looking half: live mainnet/testnet spec versions, the latest subtensor release, and a derived pending_upgrade state of none / testnet_soaking / released_undeployed / unknown. Every field is independently null on its own upstream failure, and a missing reading yields "unknown" rather than "none" — the two are opposite answers. No deploy date is predicted anywhere in the payload: the foundation publishes no schedule. Pass ?format=csv to download the transition timeline as CSV (the current_spec_version + coverage_from_* rollup and the current block stay JSON-only).