Feature flags catalogue

The authoritative user-facing reference is docs/feature_flags.md. This page is a quick index — the implementation file, the category, and the current status as of 3.11.

Flag	Category	Status	Where it's enforced
exemplar-storage	TSDB	Stable	tsdb/exemplar.go + web/api/v1/api.go
memory-snapshot-on-shutdown	TSDB	Stable	tsdb/head.go::Snapshot, replayed in Init
extra-scrape-metrics	Scrape	Deprecated	scrape/scrape.go; replaced by extra_scrape_metrics config field
promql-per-step-stats	PromQL	Stable	promql/engine.go::EngineOpts
promql-experimental-functions	PromQL Functions	Evolving	promql/parser/functions.go::Experimental
promql-duration-expr	PromQL	Stable	promql/parser/, promql/durations.go
created-timestamp-zero-ingestion	Scrape	Stable	scrape/scrape.go, model/textparse
st-storage	TSDB	New (3.11)	tsdb/head_append_v2.go, agent path
xor2-encoding	TSDB	New (3.11)	tsdb/chunkenc/xor2.go
fast-startup	TSDB	New (3.11)	tsdb/head.go
out-of-order-attributes	TSDB	Experimental	tsdb/head.go
metadata-wal-records	TSDB	Stable	tsdb/record/record.go
auto-gomaxprocs	Prometheus	Stable	cmd/prometheus/main.go
auto-gomemlimit	Prometheus	Stable	cmd/prometheus/main.go
native-histograms	TSDB	Stable	(Default-on in 3.x; flag accepted for back-compat.)
agent	Prometheus	Stable	The --agent CLI flag (not a feature flag in the registry).
enable-feature=otlp-deltatocumulative	OTLP Receiver	Experimental	storage/remote/write_otlp_handler.go
enable-feature=otlp-native-delta-ingestion	OTLP Receiver	Experimental	storage/remote/write_otlp_handler.go
old-ui	UI	Deprecation path	web/web.go
delayed-compaction	TSDB	Stable	tsdb/db.go::compact
concurrent-rule-eval	Rules	Stable	rules/group.go
head-mmap-prefault	TSDB	Experimental	tsdb/head.go

The list above is a snapshot; consult docs/feature_flags.md for descriptions, syntax, and any deprecation timelines.

How a flag is wired

--enable-feature=foo
        |
        v
flagConfig.featureList[]   (cmd/prometheus/main.go, kingpin)
        |
        v
features.Set(category, "foo", true)   (util/features)
        |
        v
relevant subsystem reads the registry during construction
        |
        v
behaviour changes
        |
        v
/api/v1/features exposes the current state

/api/v1/features returns the runtime view; the UI uses it to grey out experimental controls.

Promotion timeline

docs/feature_flags.md is updated whenever a flag changes status. The release coordinator removes flags during release cuts when:

• The behaviour is on by default.
• The flag has been deprecated for at least one minor.
• docs/migration.md documents the upgrade path.

See Feature flags feature page for the developer-facing documentation.