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Kimia’s split-engine takes any vault share and breaks it into two transferable SPL tokens:
  • PT, Principal Token. Redeems 1:1 for the underlying vault share at maturity.
  • YT, Yield Token. Captures all yield accrued between mint and maturity.
The split is conservation-preserving: PT_supply = YT_supply = escrowed_vault_shares.

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Why split?

Fixed income

Buying PT at a discount locks the yield-to-maturity as a fixed APY. You know exactly what you’ll get back.

Leveraged yield

Buying YT is pure exposure to funding. A small principal buys a claim on all future yield until maturity.

LP routing

PT/underlying pools (yield-amm) make the market: price PT = discounted future value of 1 share.

Composable receipts

PT and YT are normal SPL tokens. They can be lent, used as collateral, or routed through kUSD.

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MasterChef-style yield accounting

The engine tracks yield per YT held using the classic reward_per_share pattern: 
global:
  reward_per_share   // cumulative yield per YT, 9-decimal fixed point

per user:
  yt_balance         // YT owned
  reward_debt        // reward_per_share × yt_balance at last interaction

pending = yt_balance × reward_per_share - reward_debt
When a user joins or leaves:
  1. The engine auto-claims pending into the user’s account.
  2. yt_balance is updated.
  3. reward_debt = yt_balance × reward_per_share is reset.
This guarantees every YT holder only earns yield that accrued while they held.

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Syncing with the vault

reward_per_share is driven by the vault’s share price. Anyone can call update_rewards (a permissionless crank), which:
  1. Reads vault.share_price()
  2. Computes delta = share_price - last_vault_share_price
  3. Increments reward_per_share += delta (scaled by supply)
  4. Updates last_vault_share_price
Because the vault’s share price only moves on claim_funding, the crank cadence matches funding cadence (hourly).

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Maturity and redemption

A split-engine market is parameterized by a maturity unix timestamp.
  • Before maturity: PT trades on the yield-AMM at a discount to 1:1. Holders can claim_yield (if they also hold YT).
  • At maturity: redeem_pt becomes available, PT burns 1:1 for vault shares.
  • Early exit: Burn matched PT+YT pairs (via early_exit) to recover vault shares minus a 0.3% protocol fee, any time.

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Worked example

A user with 1,000 vault shares enters a 30-day market: 
initial:          1,000 vault shares
split:            +1,000 PT, +1,000 YT in the user's wallet
                  1,000 vault shares escrowed
sell YT:          −1,000 YT → 25 USDC (yield-AMM discount)
hold PT:          1,000 PT
at maturity:      redeem_pt → 1,000 vault shares returned
The 25 USDC is the prepaid yield, fixed and known at sale time.

Yield-AMM

The yield-space invariant that prices PT vs underlying.

Fixed-rate intents

Putting the pieces together into one session.

split-engine reference

Instructions, accounts, errors.