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.

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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.

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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:

• Constituent markets are added, and removed on published grounds, 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.

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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.

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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 and continued-eligibility criteria in Index Governance; a constituent failing maintenance at two consecutive evaluated reviews, or no longer passing an eligibility screen, is deleted at that review.
• From 2026-09-30, a constituent whose market has resolved keeps its weight at its settlement value until the next scheduled review. At that review it leaves the composition as a settlement exit – not a deletion – and the remaining constituents’ weights are scaled up in proportion; a review that also adds markets re-weights the composition as before. A constituent leaves only once its venue’s final settlement record reports the outcome; a market the venue has closed but not yet settled, or whose data is temporarily unavailable, stays a constituent at its current weight until then; while it waits it is not tested against the maintenance criteria and its strike count is carried unchanged. Missing data never removes a constituent. If every constituent of a Perpetual series has resolved, the constituents keep their settlement values, the level stays fixed, the series is shown as resolved, and it is considered for discontinuation under the cessation provisions.
• A review may conclude that no new market meets the selection criteria, in which case no market is added and the outcome is recorded; deletions and settlement exits due at that review still take effect.
• 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.

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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.

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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.

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Applying a Composition Change

A composition change is committed in a single transaction: the new composition, its weights, and the chain-link anchor are written together, and the first level on the new composition is computed immediately afterward. Some earlier reconstitutions ran through a reconstitution gate that paused the series’ publication; those intervals are recorded as gate_activated_at_utc → completed_at_utc in the reconstitutions file. If the change cannot complete, nothing is committed: the prior composition stays in effect and publication continues against it. Aborted reconstitutions are visible in the reconstitution history for the series.

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Audit Trail

Every reconstitution event produces a complete, auditable record:

• Date and time of the event.
• Markets added, with question text and condition identifiers.
• Markets removed, including settlement exits, with the ground for each deletion.
• 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, where markets that have left the composition are listed under Past constituents. Aborted reconstitutions are visible alongside completed ones.

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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 or a published settlement value, and a resolved constituent leaves only once its venue’s final settlement record reports the outcome. The level is replicable from public data.
• Valuation-window cadence. Perpetual series are valued and published on the same valuation-window cadence as Fixed series, including across reconstitutions.
• 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.

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Further Reading