> For the complete documentation index, see [llms.txt](https://docs.fira.money/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fira.money/developers/features/bond-token-bt.md). # Bond Token (BT) ## Overview BT represents a fixed-rate claim on the underlying asset. Each BT is redeemable for 1 unit of underlying at maturity. Before maturity, BT trades at a discount in the AMM — the discount reflects the implied fixed rate. {% hint style="info" %} BT and CT are always minted and burned in pairs. You cannot create BT without also creating CT, and vice versa. This ensures the total claims always match the underlying FW. {% endhint %} ## How it works ### Minting BT is created through the CouponToken's `mintBC` function. FW is deposited into the CT contract, and equal amounts of BT and CT are minted based on the current BC Index. The conversion rate ensures that `BT amount + CT amount` always equals the underlying value of the FW deposited. ### Redemption **Pre-expiry:** Both BT and CT must be provided. They are burned together and FW is returned. **Post-expiry:** Only BT is required. The CT is not burned (it has zero economic value post-expiry). FW is returned at the current BC Index rate, with any post-expiry yield accrual going to the protocol treasury. ### Trading BT trades against FW in the Fira Market AMM. As expiry approaches, the BT/FW exchange rate converges toward 1:1 (at the BC Index rate), since BT becomes redeemable for full underlying value at maturity. ## Key features * **Fixed-rate principal** — Predictable value at maturity * **Strict access control** — Only the paired CouponToken and the LiquidityInjector can mint or burn BT * **Used as loan token** — In fixed-rate lending markets, borrowers receive BT which is swapped to USDC via the router * **Immutable references** — FW address, factory, and expiry are set at creation and cannot be changed ## Related contracts * [`BondToken.sol`](/developers/protocol-contracts/yield-contracts/bond-token.md) — Contract details * [`CouponToken.sol`](/developers/protocol-contracts/yield-contracts/coupon-token.md) — Paired CT contract * [`YieldContractFactory.sol`](/developers/protocol-contracts/yield-contracts/yield-contract-factory.md) — Factory that deploys BT/CT pairs --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.fira.money/developers/features/bond-token-bt.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.