# IBTs and vault wrappers



An interest-bearing token (IBT) represents a position that can increase or decrease in underlying value. Stellar Core expects an IBT to expose a fungible-vault interface for deposits, redemptions, conversion previews, and exchange-rate accounting.

## When a wrapper is needed [#when-a-wrapper-is-needed]

A compatible fungible vault can connect to Core directly. A wrapper is needed when the yield source does not expose transferable vault shares or does not implement the expected interface.

The Stellar implementation contains:

* An abstract **Spectra Fungible Vault wrapper**, which supplies common vault, access-control, pause, upgrade, and rewards behavior.
* A concrete **Blend wrapper**, which holds a Blend lending-pool position and issues transferable shares representing its bTokens.

## Blend behavior [#blend-behavior]

Blend bTokens are positions inside a pool rather than standalone SEP-41 token contracts. The wrapper therefore owns the pool position and represents it with its own transferable shares.

<Callout type="warn">
  A wrapper is part of the backing trust boundary. A compatible interface does not prove that its exchange rate, liquidity, or accounting is safe.
</Callout>

See [Integrating IBTs and wrappers](https://dev.spectra.finance/docs/stellar/ibt-wrappers) for the contract expectations and review checklist.