2026-07-22 — AMM v4: remove OpenBook / Serum dependency

AMM v4 stopped sharing liquidity to OpenBook (formerly Serum) a long time ago; the hybrid order-book market-making path has been dormant for years. This upgrade is the cleanup: it removes the Serum dependency, all order-book CPIs, and the dead market-making instructions from the program, leaving AMM v4 as a pure constant-product (x·y=k) AMM. It does not change any live trading behavior — there were no OpenBook orders left to stop placing.

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TL;DR for integrators

• Swap / Deposit / Withdraw keep working without changes. Transactions built with the old account layouts still execute — the removed Serum/market accounts are simply ignored (no validation, no CPI). SwapBaseIn / SwapBaseOut still expect 17 (+1 optional) accounts; Deposit and Withdraw layouts are unchanged. You do not have to ship a client update to keep existing flows alive.
• Migrate to the V2 swap entrypoints. SwapBaseInV2 / SwapBaseOutV2 carry no market accounts and no amm_open_orders (8 accounts total), so transactions are smaller and cheaper. Routers/aggregators should route through V2.
• WithdrawPnl is a hard breaking change (admin only). It goes 17 (+1 optional) → 10 accounts with no compatibility parsing; the old layout misaligns (old #5 was amm_open_orders) and fails validation. Admin tooling must be updated.
• SetParams is a hard breaking change (admin only). Accounts shrink to [amm, admin], and the param enum is renumbered (Fees 9 → 2, SetOpenTime 11 → 3); AmmOwner, LastOrderDistance, UpdateOpenOrder and the grid params are removed.
• Several instructions are no longer callable. Initialize, PreInitialize, MonitorStep, MigrateToOpenBook, WithdrawSrm, SimulateInfo, and AdminCancelOrders now revert. Use Initialize2 to create pools.
• On-chain account layouts are byte-stable, and error codes are unchanged. AmmInfo / StateData keep their layout (old OpenBook fields retained but deprecated/frozen); the AmmError numbering is preserved, with only a new NotAllowed appended.

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Why this matters (for traders, LPs, and integrators)

• Traders see no change in swap behavior or pricing — the constant-product curve is unchanged. V2-layout swaps are cheaper to land because they carry ~8 fewer accounts.
• LPs keep the same deposit/withdraw economics. Liquidity has long sat entirely in the pool vaults, so pool value is fully on-pool; this upgrade only deletes the stale market plumbing.
• Integrators get smaller, simpler transactions and a quoting model that reads straight from the vaults. Existing integrations do not break (except admin WithdrawPnl / SetParams), but the v1-swap compatibility shim is temporary — migrate to V2 at your convenience.

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Instruction-level changes

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Still callable, layout unchanged (backward compatible)

Initialize2, Deposit, Withdraw, SwapBaseIn, SwapBaseOut, CreateConfigAccount, and UpdateConfigAccount keep their existing account lists. On SwapBaseIn / SwapBaseOut, Deposit, and Withdraw the OpenBook/market accounts are still accepted positionally but are no longer validated or used — no CPI is issued and pool reserves are computed vault-only. The account count must still match, so existing transactions continue to execute unchanged.

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SwapBaseInV2 / SwapBaseOutV2 — recommended path

Omit the market accounts and amm_open_orders entirely (8 accounts; tags 16 / 17). Quote math is identical to v1. New integrations and routers should use V2.

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WithdrawPnl — 17 (+1 optional) → 10 accounts (⚠️ hard breaking, no compatibility path)

amm_open_orders and all six market accounts are removed. The new fixed 10-account, admin-only layout has no compatibility parsing; the old layout misaligns and fails with errors such as InvalidCoinVault.

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SetParams — reduced to [amm, admin] (⚠️ hard breaking) + renumbered params

The authority, open-orders, target-orders, vault, and all market accounts are removed. The param enum is renumbered and trimmed: All order-book-grid params (OrderNum, Depth, AmountWave, MinPriceMultiplier, MaxPriceMultiplier, MinSize, VolMaxCutRatio, InitOrderDepth, SetSwitchTime, ClearOpenTime, Seperate) plus AmmOwner, LastOrderDistance, and UpdateOpenOrder are removed. The SetParamsInstruction struct drops new_pubkey and last_order_distance.

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No longer callable (revert at runtime; builders removed)

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Reserve / state changes

• Pool-asset formula. Total pool assets are now vault balances − pending PnL (need_take_pnl); the OpenBook open-order term — already zero in practice — is dropped. Quoting code can read straight from the vault balances.
• Deprecated state fields. StateData.total_pnl_pc, total_pnl_coin, orderbook_to_init_time, swap_coin_in_amount, swap_pc_out_amount, swap_acc_pc_fee, swap_pc_in_amount, swap_coin_out_amount, and swap_acc_coin_fee are retained for layout compatibility but no longer updated. Consumers relying on the swap_* volume counters should switch to trade logs.
• AmmInfo init. coin_lot_size, pc_lot_size, and min_size are now initialized to 0.
• Removed dependency and CPIs. The serum_dex crate is dropped from Cargo.toml; all Serum DEX CPIs (invoke_dex_new_order_v3, invoke_dex_cancel_order_v2, invoke_dex_settle_funds, invoke_dex_init_open_orders, …) are removed from invokers.rs. Removed data structs: LastOrderDistance, SimulateParams, RunCrankData, GetPoolData, GetSwapBaseInData, GetSwapBaseOutData.