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BreakingApril 17, 2026

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Overview

The concentrated liquidity design for RWT master pools has been redesigned from a symmetric 2:1 pyramid with periodic range-shifts to a Monotonic Ladder — a single-sided, cumulatively growing bid structure that uses rwt_engine::mint_rwt as a synthetic ask-side. This change doubles effective capital efficiency of Nexus LP, eliminates ask-side impermanent-loss-style drift on NAV appreciation, and replaces stateful range repositioning with additive growth.

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Why Change

The prior 2:1 pyramid was a direct adaptation of standard CL-AMM patterns (Meteora, Trader Joe). It assumed RWT price could drift in both directions, so both sides of the book needed pre-funded liquidity. Three properties of RWT invalidate that assumption:
  1. NAV is monotonically non-decreasing in normal operation (70% of yield accrues to book value, no redeem)
  2. mint_rwt is an always-on ask-side at deterministic price NAV × 1.01. Any pre-funded RWT above NAV × 1.005 is economically dead capital — buyers always prefer mint
  3. Exit liquidity is the scarce resource — holders need deep bid; buyers already have unlimited mint depth
The new design fits these properties exactly.

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What Changed

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Before (Symmetric Pyramid)

70-bin BinArray, 40 active bins centered on NAV
Asymmetric 2:1 pyramid: 2/3 USDC below NAV, 1/3 RWT above NAV
shift_liquidity: moves entire range when NAV drifts > 1%
  — drains old far-left/far-right bins
  — redistributes to new range around current NAV
  — effectively "sells" old-NAV RWT when NAV rises (ask-side IL)
Problems:
  • ~33% of LP capital sat in RWT ask-side that was economically dead (mint cheaper)
  • Rebalance on NAV growth forced LPs out of appreciating RWT positions
  • BinArray size limited cumulative growth to ~7% before hitting bounds
  • No distinction between “permanent stress buffer” and “active trading zone”

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After (Monotonic Ladder)

1000-bin log-scale BinArray (MAX_BINS = 1000)
Three zones:
  1. Permanent tail: thin USDC at [initial_NAV - 1% .. initial_NAV - 0.3%]
     — immutable, never shifted, historical floor for protocol lifetime
  2. Active bid wall: dense USDC, geometric density r = 0.85
     — peak at active_bin, extends leftward through extended bid
  3. Organic ask: RWT accumulated from user sells
     — not pre-funded, not managed by Rebalancer

Nexus LP deposits USDC only. RWT never pre-deposited to master pools.

Instructions:
  shift_liquidity        → removed
  grow_liquidity         → NEW: extends bid wall rightward as NAV rises
                           Pulls fresh USDC from Nexus accumulator
                           Permanent tail and organic ask untouched
  compress_liquidity     → NEW: recenters density on lower NAV after writedown
                           Frozen ask-wall preserved for recovery
                           Capital never destroyed

Swap (USDC → RWT, master pools only):
  If organic ask exists AND price ≤ NAV × 1.005:
    → bin-walk swap, LP and protocol fees apply
  Else:
    → CPI rwt_engine::mint_rwt
    → NO DEX fee charged (mint fee already compensates DAO)
Benefits:
  • 100% of Nexus LP is productive (bid-side only) — ~2× capital efficiency
  • LPs never forced to sell RWT on NAV appreciation (no ask-side IL)
  • Cumulative structure: every historical NAV level retains bid depth forever
  • 1000-bin array at 0.1% step covers NAV × 2.7 growth (~10+ years at 7% APY)
  • Mint routing guarantees deterministic worst-case ask price
  • Self-reinforcing depth flywheel: NAV↑ → yield↑ → Nexus USDC inflow↑ → bid depth↑

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Breaking Changes

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Contract interface

InstructionStatus
shift_liquidityRemoved
grow_liquidityNew — signature includes liquidity_nexus and nexus_usdc_ata accounts
compress_liquidityNew — no Nexus accounts (capital-neutral)
swapChanged — master-pool USDC→RWT path now branches on ask availability and mint price; additional accounts required (rwt_vault, rwt_mint, capital_accumulator_ata, dao_fee_account, user_rwt)
create_concentrated_poolChanged — new permanent_tail_offset_bps parameter; non-RWT side must be USDC or USDY; BinArray sized for 1000 bins
add_liquidity / zap_liquidityRestricted — fails with MasterPoolUserLpDisabled on Monotonic Ladder pools (StandardCurve unaffected)

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State

  • BinArray PDA size: ~32 KB (was ~2 KB for 70 bins). Rent: ~0.22 SOL per master pool.
  • PoolState adds: left_anchor_bin, permanent_tail_floor_bin, last_rebalance_nav_bin, active_zone_lower.

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Off-chain services

  • Pool Rebalancer logic split into growth path (grow_liquidity) and compression path (compress_liquidity). Adds checks for Nexus accumulator availability before growth calls.

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Unchanged

  • StandardCurve pools (OT/RWT, third-party pairs) — no change in behavior, math, or fee structure
  • Per-pool fee vault and claim_lp_fees model (for bin-path swaps)
  • compound_yield for OT pools (unchanged)
  • OT Treasury fee on OT pairs (unchanged)
  • mint_rwt mechanics (no change in fee split or NAV accounting)

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Migration

This is a protocol-design change, not a live-state migration — master pools have not yet launched on mainnet. Developers implementing from the updated spec should disregard prior shift_liquidity references and the 70-bin / 2:1 pyramid semantics.