Charon Feature Flags

How Charon's feature flags gate alpha and beta functionality, and how operators can enable, disable, or observe them.

Charon ships in-development functionality behind feature flags before it becomes the default behavior. This lets the Obol team roll out new consensus timers, client integrations, and other changes gradually, and lets operators opt in to (or out of) specific behavior on their own nodes.

Maturity Statuses

Every feature flag has a maturity status:

• Alpha - for internal devnet testing. Behavior may change or be removed without notice.

• Beta - for internal and external testnet testing. More stable than alpha, but not yet proven in production.

• Stable - ready for production. Stable features are enabled by default.

Charon only enables features at or above a configured minimum status. By default, that minimum is stable, so only stable features run unless an operator explicitly changes the configuration.

Enabling alpha or beta features on a mainnet cluster is done at the operator's own risk — these features are still being validated and may change or be withdrawn in a future release. Because Charon nodes reach agreement through consensus, features that affect consensus-relevant behavior (for example, round timers or attestation data fetching) generally need to be enabled consistently across all nodes in a cluster; mismatched feature sets between operators can cause the affected nodes to diverge from the rest of the cluster.

Enabling and Disabling Feature Flags

Feature flags are controlled with three charon run flags (each with a matching CHARON_ environment variable, following Charon's standard flag-to-env-var convention):

Flag	Environment Variable	Description
--feature-set	CHARON_FEATURE_SET	Minimum feature set to enable by default: alpha, beta, or stable. Defaults to stable.
--feature-set-enable	CHARON_FEATURE_SET_ENABLE	Comma-separated list of individual features to enable, overriding the default minimum feature set.
--feature-set-disable	CHARON_FEATURE_SET_DISABLE	Comma-separated list of individual features to disable, overriding the default minimum feature set.

--feature-set-enable and --feature-set-disable take precedence over --feature-set on a per-feature basis, so an operator can, for example, run with the default stable minimum while explicitly enabling a single alpha feature for testing.

Example docker-compose.yml snippet enabling one alpha feature while leaving everything else at the stable default:

services:
  charon:
    environment:
      - CHARON_FEATURE_SET=stable
      - CHARON_FEATURE_SET_ENABLE=json_requests

Current Feature Flags

This table reflects Charon v1.10.0-dev (commit 094953a). Feature flags are added and removed between releases as functionality graduates to stable and is eventually always-on, so check the CLI reference or run charon run --help for the current, authoritative list.

Flag Name	Status	Default	Description
eager_double_linear	Stable	Enabled	Uses an eager double-linear round timer for consensus rounds.
consensus_participate	Stable	Enabled	Lets a node participate in an ongoing consensus round while it is still waiting for unsigned duty data from its beacon node.
proposal_timeout	Stable	Enabled	Uses a longer, 1.5-second first consensus round timeout for proposal duties.
fetch_only_commidx_0	Stable	Enabled	Queries the beacon node for attestation data only for committee index 0.
linear	Alpha	Disabled	Uses a linear round timer for consensus rounds; takes precedence over eager_double_linear when both are active.
aggsigdb_v2	Alpha	Disabled	Uses a newer, simpler implementation of the aggsigdb component.
json_requests	Alpha	Disabled	Uses JSON (instead of SSZ) requests when talking to the eth2 beacon node client.
gnosis_block_hotfix	Alpha	Disabled (auto-enabled on Gnosis/Chiado)	Applies an SSZ fix required by the Gnosis and Chiado networks. Charon automatically enables this feature when the configured network is Gnosis or Chiado, unless an operator explicitly disables it.
sse_reorg_duties	Alpha	Disabled	Lets the scheduler refresh duties when a chain reorg occurs.
attestation_inclusion	Alpha	Disabled	Tracks on-chain inclusion of attestations. This was previously always-on behavior, but tracking inclusion after the Electra upgrade adds enough load on the beacon node that it can throttle other duties, so it is now opt-in.
quic	Alpha	Disabled	Enables the QUIC transport protocol in libp2p networking.
chain_split_halt	Alpha	Disabled	Compares the locally fetched attestation's target and source against the leader's proposed attestation; if they differ, Charon does not sign the attestation.
fetch_att_on_block	Alpha	Disabled	Fetches attestation data as soon as a block-processing event is received from the beacon node over SSE, falling back to the standard one-third-of-slot timing if no block event arrives in time.
fetch_att_on_block_with_delay	Alpha	Disabled	Fetches attestation data with an added 300ms delay. Combined with fetch_att_on_block, uses one-third-of-slot-plus-300ms as the fallback timeout; used alone, it uses that same timeout directly.
disable_duties_cache	Alpha	Disabled	Safety switch to disable the internal duties cache.
mock_alpha	Alpha	Disabled	Internal/experimental placeholder feature used only for testing the feature flag system itself; it has no functional effect.

Observing Enabled Feature Flags

Charon exposes the app_feature_flags Prometheus metric, a constant gauge labeled with any non-default (custom-enabled) feature flags currently active on a node. See the Charon Metrics Reference for the full metrics list and label details. Comparing this metric across nodes in a cluster is a quick way to confirm that operators have matching feature sets for consensus-relevant flags.

Related Reading

• CLI Reference - full list of charon run flags, including --feature-set, --feature-set-enable, and --feature-set-disable.

• Consensus Protocols - background on Charon's consensus layer, relevant to feature flags like eager_double_linear, linear, and consensus_participate.