> For the complete documentation index, see [llms.txt](https://docs.aquaflux.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aquaflux.pro/the-primitives/tri-token-model/s-token-shield-and-surplus.md). # S-Token (Shield & Surplus) "Shield + Surplus Yield = Smart Alpha" **S-Token** is the "High Yield" engine of AquaFlux. It is designed for users who want to earn significantly more than the standard rate and are comfortable taking on the role of a **Risk Underwriter**. ### What it is S-Token S-Token is the Shield, first-loss buffer that protects P and C. In return, it can earn a Surplus yield: a slice of *coupons*, a share of *protocol fees,* and a possible *points or airdrop* reward from issuer. ### The Core Concept: You are the Insurer The best way to understand S-Token is through an insurance analogy: * P-Token Holders are the **Insured**. They accept a lower return in exchange for safety. * S-Token Holders are the **Insurers**. You provide that safety (First-Loss protection). Why do it? Because insurers get paid **Premiums**. In AquaFlux, these "premiums" come in two powerful forms: 1. **Intrinsic Yield** (S-Token): The base asset's yield + fees. 2. **Extrinsic Rewards** (SS, Staked S-Token): The protocol's incentive rewards + upside. ### S-Token (Shield, The Underwriter) By holding S-Token, you are the **Underwriter** of the pool. This position gives you two powerful rights: 1. **The Yield**: You earn a share of the **underlying asset's principal and coupon**. It's the intrinsic cash flow from the asset itself. 2. **The Exclusive Ticket**: S-Token is the **only way** to access **SS (Surplus)**. Think of S-Token as your membership pass—without it, you cannot participate in the underlying's future upside. **The Risk (First-Loss)** Just like an insurance company, if valid claims are made (i.e., the asset defaults or loses value), you pay first. Your capital absorbs the loss to protect P-Token holders. ### SS (Staked S, The Bonus) This is the "Hidden Gem" of the system. While S-Token captures the asset's yield, **SS (Surplus)** captures the protocol's upside. **Crucial Rule:** 1. **Stake S-Token**: Stake your S-Tokens into the protocol. * *Note: Once staked, your S-Tokens are **locked until the asset matures**. You cannot unstake early.* 2. **Earn SS Linearly**: SS is generated continuously based on your staked amount. The more you stake and the longer you wait, the more SS you earn. 3. **Claim & Trade Anytime**: While your S-Token is staked, your earned **SS is liquid**. You can claim your SS rewards at any time and sell them on the secondary market if you wish. **Think of it this way**: * **Staking S** = Planting a tree. You can't move the tree until harvest season (Maturity). * **Receiving SS** = Gathering fruit. You can pick and sell the fruit (SS) whenever you want, while the tree continues to grow. ***
*** ### How it works * **Loss waterfall** * **S-Token** absorbs losses first (up to its coverage). * If losses exceed S, **C-Token** is reduced next. * Only extreme residual loss may reach **P-Token**. * **Cash flows to S** * **Coupon share:** A fixed % of each coupon payment. * **Protocol fees:** A defined % of AquaFlux fees (swap/wrap/split/merge/LP fees, etc.—see dApp). * **Issuer incentives:** A possible points or airdrop reward from issuer. * **Pricing (no hard par):**\ S’s fair value ≈ *(expected coupon share + expected fees + expected residual)* − *(expected losses)*.\ Expectations change with asset quality, coverage ratio, time to maturity, and market sentiment. ### Who it’s for * **Yield hunters / risk takers** who understand first-loss dynamics. * **Structured-yield strategies** selling downside in exchange for higher carry. ### Acquire & Exit * **Acquire** * Wrap a supported RWA and **Split** into P/C/S. * **Buy** S-Token directly in the pool/AMM. * **Exit** * **Sell anytime** at market price (T+0). * **At maturity**: if the bond repays in full, any **unused** S buffer + final fee/coupon shares are distributed to S holders. If losses occurred, your S position may be partially/fully reduced. ### S Tranche Valuation **Definition**\ The S-Token is the junior, first-loss tranche. Its present value (PV) is the sum of upside components minus expected loss: $$ \mathrm{PV}*{S}=\mathrm{PV}*{\text {coupon share }}+\mathrm{PV}*{\text {fee share }}+\mathrm{PV}*{\text {points/airdrop }}-\mathrm{PV}\_{\text {expected loss }} $$ *** Now, let's decompose each term in the formula, let's define * Face value per unit: **N** (e.g., N=100). * Time to maturity: **T** (years). * Discount rate: **r** (annual; discount via (1+r)). * Bond coupon rate: **c** (annual). * Coupon share to S: **γ** (e.g., 20% of total coupon). * Pool fee rate per swap: **f** (e.g., 0.20%). * Annual turnover (volume/TVL): **v** (turnover per year). * Protocol fee split to S: **α** (e.g., 50%). 1. **Coupon Share** If coupon is realized at maturity: $$ \text{PV}\_{\text{coupon share}} = \frac{\gamma c N}{(1 + r)^T} $$ 2. **Fee Share** You can check the exact fee accumulation in the **on-chain vault**. And you can also use the following methods to make an estimate. Currently this mainly considering AMM fees, and we will add split/merge, wrap/unwarp fees later. Annual fees attributable to notional **N**: $$ Feeyear=f⋅v⋅N $$ S receives fraction: $$ \text{PV}\_{\text{fee share}} \approx \frac{\alpha f v N}{(1 + r)^{T}} $$ 3. **Points / Airdrop** You need to calculate according to the specific airdrop rules. * **Check the rule:** emission pace, eligible actions (LP, stake, quests), and any **boosts**. * **Time matters:** count only **active days** you expect to participate. * **Apply a haircut:** reflect eligibility risk, snapshot timing, vesting/lockups, and token-price uncertainty. 4. **Expected Loss** You can use different risk models to calculate. S is the **first-loss** tranche. Keep it simple with a blended annual loss assumption: * **Use bands, not a single number:** Conservative / Base / Optimistic. * **What drives it:** issuer quality, asset health, **S coverage** (thicker S = more buffer), diversification, and historical behavior. * **Cap awareness:** S’s annual loss cannot exceed its **coverage size**; excess loss would waterfall to senior tranches. * **Update cadence:** revisit after material events (audits, covenant breaches, ratings watch, liquidity stress). * **Presentation:** show the three bands alongside key context (coverage %, asset type, tenor) and note that it’s a **prudential estimate**. ### FAQ * **Is S-Token principal-protected?**\ No. It’s **first-loss** by design. You are compensated via coupon share, fee share, and potential residual—**not** by a 1:1 redemption promise. * **Does buying S-Token give me insurance on the asset?**\ No. Buying S-Token is like **selling** insurance—you act as the first-loss provider (the underwriter). You earn coupon/fee shares and potential residuals for taking that risk, and you’re hit first if losses occur. If you want to **buy** protection instead, do the opposite: **short the S-Token** or avoid S and hold **P (or P + C)** so the first-loss buffer works in your favor. * **When do I earn?**\ Throughout the term (coupon/fee distributions) and potentially at maturity (unused buffer), provided performance is on track. * **What happens if there’s a default?**\ S is reduced first. If the loss exceeds S, it then hits C, and only then P. * **Can S-Token go to zero?**\ Yes, in severe loss scenarios. Size positions accordingly. * **Why do S-Tokens price so differently?**\ Coverage %, asset quality, expected recoveries, time to maturity, and market liquidity all drive expected carry vs. expected loss.