Perpetual Series

Belief Index series are classified by Maturity Type: Fixed or Perpetual. The distinction determines whether the series has a defined endpoint or whether its composition evolves over time.

​

Fixed vs. Perpetual at a Glance

Belief Systems publishes both Fixed and Perpetual series. Perpetual is the right classification for thematic series whose underlying domain evolves over time – for example, indices tracking geopolitical conflict risk where new prediction markets emerge as new situations develop.

​

The Analogy

A Perpetual series works like a reconstituting equity index. The S&P 500 does not hold the same 500 companies forever – its index committee periodically adds and removes constituents as the market evolves, and the index level remains continuous across those reconstitutions. A Perpetual Belief Index series follows the same convention:

• New constituent markets are added through a formal reconstitution event initiated by Belief Systems.
• The change is a calculation-level operation: the new composition and its weights are written, and the level is re-anchored to it. No trading takes place — Belief Index series are theoretical baskets, not portfolios.
• The reported index level is continuous across the event – no visible step in the chart.

​

Market Selection Criteria

Candidate markets for inclusion in a Perpetual series are evaluated across six dimensions. Most are enforced as hard numeric thresholds – the current values, and the weighting formula applied to admitted markets, are published in Market Selection & Weighting. The same rule set governs the series’ initial composition, so a market that qualifies at creation would also qualify at reconstitution. Individual series may apply additional theme-specific criteria on top of this baseline – those are disclosed on the series detail page when present.

​

Review Cadence

Each Perpetual series specifies a review cadence at creation. The default cadence is monthly.

• The review cadence is a commitment to evaluate the series composition on that frequency – not a commitment to change it.
• A review also tests existing constituents against the maintenance criteria in Index Governance; a constituent failing them at two consecutive reviews becomes a deletion candidate. A review may conclude that no new market meets the selection criteria, in which case the composition is unchanged and the outcome is recorded.
• The review cadence is displayed on each series’ detail page.

Belief Systems commits to a consistent review rhythm rather than ad-hoc reconstitution. Reviews that result in no change are still reviews; the discipline is in the schedule, not in any given outcome.

​

Chain-Linking (Index Continuity)

When composition changes, the raw probability-weighted aggregate (raw_nav) changes mechanically – different markets, different weights, different numbers. A Perpetual series uses chain-linking to ensure the reported index level is continuous across the change. The arithmetic is a single Decimal expression evaluated to 8 decimal places. The chart is continuous; the composition change is reflected only in the underlying market breakdown.

Why `raw_nav` is not continuous but `index_level` is

raw_nav is a snapshot of the current composition’s probability-weighted aggregate. When the composition changes, raw_nav changes too – it has to, because the markets and weights are different. index_level is the published time series; chain-linking re-anchors inception_raw_nav at each reconstitution so that index_level stays continuous even as the underlying basket evolves. The chain-link formula and a worked example are in Index Calculation Methodology – Chain-Linking.

​

Replication Cost (Not Reflected in the Index)

A Belief Index level is a theoretical measurement. Anyone attempting to replicate a basket in the underlying markets would pay spreads, slippage, and order-placement costs, and would pay them again at each reconstitution. That cost is real, and it is not deducted from the published level – exactly as an equity index is published gross of the trading costs an index fund incurs tracking it.

• The published level is theoretical throughout: it never reflects an executed trade.
• Replication cost is disclosed as a methodology limitation, not netted into the number. See Risk Factors.

​

The Reconstitution Gate

During a reconstitution, the series enters a gate – a planned, bounded pause on publication while the composition change is written and verified. The gate lifts automatically on success – when the new composition is committed, the chain-link anchor is written, and verification passes. No manual acknowledgment is required to resume publication. If the change cannot complete, the reconstitution follows an abort path: the old composition is restored and the gate lifts. Aborted reconstitutions are visible in the reconstitution history for the series.

​

Audit Trail

Every reconstitution event produces a complete, auditable record:

• Date and time of the event.
• Markets added, with question text and condition identifiers.
• Weight changes: before and after, for each market.
• Chain-link anchor: the index level preserved across the event.
• Composition version: the before and after SHA256-tagged identifiers.
• Event status: completed or aborted, with reason.

The reconstitution history is visible on the series detail page. Aborted reconstitutions are visible alongside completed ones.

​

What This Does Not Change

Everything else about how a Belief Index series works continues to hold for Perpetual series:

• Observable inputs. Every constituent price is a public order book midprice, and every resolution is confirmed against on-chain settlement state. The level is replicable from public data.
• Valuation-window cadence. Outside of the gate, Perpetual series are valued and published on the same valuation-window cadence as Fixed series.
• Rules-based methodology. Market selection for inclusion in a Perpetual series follows the published eligibility screens and weighting formula in Market Selection & Weighting.
• Full audit trail. Every reconstitution event produces a complete record – composition version from and to, chain-link anchor, and event outcome.

​

Further Reading