solana-foundation · jacobcreech · Dec 9, 2025 · Aug 28, 2025 · Aug 28, 2025 · Aug 28, 2025
diff --git a/.github/workflows/reusable-tests.yaml b/.github/workflows/reusable-tests.yaml
@@ -418,6 +418,8 @@ jobs:
             path: tests/custom-program
           - cmd: cd tests/typescript && anchor test --skip-lint && npx tsc --noEmit
             path: tests/typescript
+          - cmd: cd tests/duplicate-mutable-accounts && anchor test --skip-lint
+            path: tests/duplicate-mutable-accounts
           # zero-copy tests cause `/usr/bin/ld: final link failed: No space left on device`
           # on GitHub runners. It is likely caused by `cargo test-sbf` since all other tests
           # don't have this problem.

diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -20,6 +20,8 @@ The minor version will be incremented upon a breaking change and the patch versi
 
 ### Breaking
 
+- lang: Disallow duplicate mutable accounts by default. But allows duplicate mutable accounts in instruction contexts using `dup` constraint ([#3946](https://github.com/solana-foundation/anchor/pull/3946)).
+
 ## [0.32.1] - 2025-10-09
 
 ### Features

diff --git a/bench/BINARY_SIZE.md b/bench/BINARY_SIZE.md
@@ -16,9 +16,9 @@ The programs and their tests are located in [/tests/bench](https://github.com/co
 
 Solana version: 2.3.0
 
-| Program | Binary Size | -                        |
-| ------- | ----------- | ------------------------ |
-| bench   | 932,424     | 🟢 **-194,416 (17.25%)** |
+| Program | Binary Size | -                       |
+| ------- | ----------- | ----------------------- |
+| bench   | 1,015,624   | 🟢 **-111,216 (9.87%)** |
 
 ### Notable changes
 

diff --git a/bench/COMPUTE_UNITS.md b/bench/COMPUTE_UNITS.md
@@ -18,93 +18,93 @@ Solana version: 2.3.0
 
 | Instruction                 | Compute Units | -                     |
 | --------------------------- | ------------- | --------------------- |
-| accountInfo1                | 702           | 🔴 **+17 (2.48%)**    |
-| accountInfo2                | 1,124         | 🔴 **+71 (6.74%)**    |
-| accountInfo4                | 1,921         | 🔴 **+171 (9.77%)**   |
-| accountInfo8                | 3,480         | 🔴 **+345 (11.00%)**  |
+| accountInfo1                | 760           | 🔴 **+75 (10.95%)**   |
+| accountInfo2                | 1,180         | 🔴 **+127 (12.06%)**  |
+| accountInfo4                | 1,952         | 🔴 **+202 (11.54%)**  |
+| accountInfo8                | 3,530         | 🔴 **+395 (12.60%)**  |
 | accountEmptyInit1           | 4,770         | 🟢 **-145 (2.95%)**   |
-| accountEmpty1               | 738           | 🟢 **-36 (4.65%)**    |
+| accountEmpty1               | 773           | 🟢 **-1 (0.13%)**     |
 | accountEmptyInit2           | 8,487         | 🟢 **-306 (3.48%)**   |
-| accountEmpty2               | 1,138         | 🟢 **-36 (3.07%)**    |
+| accountEmpty2               | 1,173         | 🟢 **-1 (0.09%)**     |
 | accountEmptyInit4           | 15,915        | 🟢 **-833 (4.97%)**   |
-| accountEmpty4               | 1,923         | 🟢 **-39 (1.99%)**    |
+| accountEmpty4               | 1,960         | 🟢 **-2 (0.10%)**     |
 | accountEmptyInit8           | 30,779        | 🟢 **-1,578 (4.88%)** |
-| accountEmpty8               | 3,500         | 🟢 **-48 (1.35%)**    |
+| accountEmpty8               | 3,539         | 🟢 **-9 (0.25%)**     |
 | accountSizedInit1           | 4,864         | 🟢 **-155 (3.09%)**   |
-| accountSized1               | 786           | 🟢 **-36 (4.38%)**    |
+| accountSized1               | 820           | 🟢 **-2 (0.24%)**     |
 | accountSizedInit2           | 8,654         | 🟢 **-327 (3.64%)**   |
-| accountSized2               | 1,198         | 🟢 **-42 (3.39%)**    |
+| accountSized2               | 1,236         | 🟢 **-4 (0.32%)**     |
 | accountSizedInit4           | 16,236        | 🟢 **-918 (5.35%)**   |
-| accountSized4               | 2,031         | 🟢 **-51 (2.45%)**    |
+| accountSized4               | 2,070         | 🟢 **-12 (0.58%)**    |
 | accountSizedInit8           | 31,363        | 🟢 **-1,650 (5.00%)** |
-| accountSized8               | 3,694         | 🟢 **-68 (1.81%)**    |
+| accountSized8               | 3,731         | 🟢 **-31 (0.82%)**    |
 | accountUnsizedInit1         | 4,967         | 🟢 **-160 (3.12%)**   |
-| accountUnsized1             | 814           | 🟢 **-60 (6.86%)**    |
+| accountUnsized1             | 854           | 🟢 **-20 (2.29%)**    |
 | accountUnsizedInit2         | 8,841         | 🟢 **-410 (4.43%)**   |
-| accountUnsized2             | 1,240         | 🟢 **-86 (6.49%)**    |
+| accountUnsized2             | 1,281         | 🟢 **-45 (3.39%)**    |
 | accountUnsizedInit4         | 16,559        | 🟢 **-819 (4.71%)**   |
-| accountUnsized4             | 2,093         | 🟢 **-138 (6.19%)**   |
+| accountUnsized4             | 2,134         | 🟢 **-97 (4.35%)**    |
 | accountUnsizedInit8         | 31,985        | 🟢 **-1,976 (5.82%)** |
-| accountUnsized8             | 3,797         | 🟢 **-238 (5.90%)**   |
+| accountUnsized8             | 3,837         | 🟢 **-198 (4.91%)**   |
 | boxedAccountEmptyInit1      | 4,864         | 🟢 **-143 (2.86%)**   |
-| boxedAccountEmpty1          | 831           | 🟢 **-33 (3.82%)**    |
+| boxedAccountEmpty1          | 864           | -                     |
 | boxedAccountEmptyInit2      | 8,604         | 🟢 **-302 (3.39%)**   |
-| boxedAccountEmpty2          | 1,253         | 🟢 **-33 (2.57%)**    |
+| boxedAccountEmpty2          | 1,285         | 🟢 **-1 (0.08%)**     |
 | boxedAccountEmptyInit4      | 16,075        | 🟢 **-827 (4.89%)**   |
-| boxedAccountEmpty4          | 2,077         | 🟢 **-38 (1.80%)**    |
+| boxedAccountEmpty4          | 2,112         | 🟢 **-3 (0.14%)**     |
 | boxedAccountEmptyInit8      | 31,026        | 🟢 **-1,565 (4.80%)** |
 | boxedAccountEmpty8          | 3,797         | 🟢 **-4 (0.11%)**     |
 | boxedAccountSizedInit1      | 4,952         | 🟢 **-151 (2.96%)**   |
-| boxedAccountSized1          | 877           | 🟢 **-35 (3.84%)**    |
+| boxedAccountSized1          | 913           | 🔴 **+1 (0.11%)**     |
 | boxedAccountSizedInit2      | 8,756         | 🟢 **-319 (3.52%)**   |
-| boxedAccountSized2          | 1,318         | 🟢 **-37 (2.73%)**    |
+| boxedAccountSized2          | 1,351         | 🟢 **-4 (0.30%)**     |
 | boxedAccountSizedInit4      | 16,355        | 🟢 **-859 (4.99%)**   |
-| boxedAccountSized4          | 2,185         | 🟢 **-46 (2.06%)**    |
+| boxedAccountSized4          | 2,218         | 🟢 **-13 (0.58%)**    |
 | boxedAccountSizedInit8      | 31,562        | 🟢 **-1,959 (5.84%)** |
 | boxedAccountSized8          | 3,984         | 🟢 **-23 (0.57%)**    |
 | boxedAccountUnsizedInit1    | 5,044         | 🟢 **-158 (3.04%)**   |
-| boxedAccountUnsized1        | 907           | 🟢 **-57 (5.91%)**    |
+| boxedAccountUnsized1        | 943           | 🟢 **-21 (2.18%)**    |
 | boxedAccountUnsizedInit2    | 8,916         | 🟢 **-335 (3.62%)**   |
-| boxedAccountUnsized2        | 1,352         | 🟢 **-82 (5.72%)**    |
+| boxedAccountUnsized2        | 1,386         | 🟢 **-48 (3.35%)**    |
 | boxedAccountUnsizedInit4    | 16,651        | 🟢 **-891 (5.08%)**   |
-| boxedAccountUnsized4        | 2,234         | 🟢 **-133 (5.62%)**   |
+| boxedAccountUnsized4        | 2,270         | 🟢 **-97 (4.10%)**    |
 | boxedAccountUnsizedInit8    | 32,130        | 🟢 **-2,023 (5.92%)** |
 | boxedAccountUnsized8        | 4,063         | 🟢 **-194 (4.56%)**   |
-| boxedInterfaceAccountMint1  | 1,092         | 🟢 **-18 (1.62%)**    |
-| boxedInterfaceAccountMint2  | 1,490         | 🟢 **-44 (2.87%)**    |
-| boxedInterfaceAccountMint4  | 2,276         | 🟢 **-94 (3.97%)**    |
+| boxedInterfaceAccountMint1  | 1,128         | 🔴 **+18 (1.62%)**    |
+| boxedInterfaceAccountMint2  | 1,523         | 🟢 **-11 (0.72%)**    |
+| boxedInterfaceAccountMint4  | 2,307         | 🟢 **-63 (2.66%)**    |
 | boxedInterfaceAccountMint8  | 3,907         | 🟢 **-157 (3.86%)**   |
-| boxedInterfaceAccountToken1 | 1,219         | 🟢 **-27 (2.17%)**    |
-| boxedInterfaceAccountToken2 | 1,732         | 🟢 **-62 (3.46%)**    |
-| boxedInterfaceAccountToken4 | 2,748         | 🟢 **-130 (4.52%)**   |
+| boxedInterfaceAccountToken1 | 1,255         | 🔴 **+9 (0.72%)**     |
+| boxedInterfaceAccountToken2 | 1,765         | 🟢 **-29 (1.62%)**    |
+| boxedInterfaceAccountToken4 | 2,779         | 🟢 **-99 (3.44%)**    |
 | boxedInterfaceAccountToken8 | 4,839         | 🟢 **-229 (4.52%)**   |
-| interfaceAccountMint1       | 1,107         | 🟢 **-19 (1.69%)**    |
-| interfaceAccountMint2       | 1,494         | 🟢 **-68 (4.35%)**    |
-| interfaceAccountMint4       | 2,276         | 🟢 **-156 (6.41%)**   |
+| interfaceAccountMint1       | 1,145         | 🔴 **+19 (1.69%)**    |
+| interfaceAccountMint2       | 1,533         | 🟢 **-29 (1.86%)**    |
+| interfaceAccountMint4       | 2,313         | 🟢 **-119 (4.89%)**   |
 | interfaceAccountMint8       | 3,835         | 🟢 **-328 (7.88%)**   |
-| interfaceAccountToken1      | 1,239         | 🟢 **-29 (2.29%)**    |
-| interfaceAccountToken2      | 1,753         | 🟢 **-96 (5.19%)**    |
-| interfaceAccountToken4      | 2,783         | 🟢 **-214 (7.14%)**   |
-| interface1                  | 883           | 🔴 **+5 (0.57%)**     |
-| interface2                  | 1,029         | 🔴 **+6 (0.59%)**     |
-| interface4                  | 1,308         | 🔴 **+7 (0.54%)**     |
-| interface8                  | 1,887         | 🔴 **+20 (1.07%)**    |
-| program1                    | 899           | 🔴 **+9 (1.01%)**     |
-| program2                    | 1,049         | 🔴 **+14 (1.35%)**    |
-| program4                    | 1,336         | 🔴 **+23 (1.75%)**    |
-| program8                    | 1,917         | 🔴 **+38 (2.02%)**    |
-| signer1                     | 888           | 🔴 **+14 (1.60%)**    |
-| signer2                     | 1,244         | 🔴 **+71 (6.05%)**    |
-| signer4                     | 1,904         | 🔴 **+145 (8.24%)**   |
-| signer8                     | 3,293         | 🔴 **+352 (11.97%)**  |
-| systemAccount1              | 910           | 🟢 **-1 (0.11%)**     |
-| systemAccount2              | 1,269         | 🔴 **+34 (2.75%)**    |
-| systemAccount4              | 1,972         | 🔴 **+101 (5.40%)**   |
-| systemAccount8              | 3,385         | 🔴 **+232 (7.36%)**   |
-| uncheckedAccount1           | 896           | 🔴 **+14 (1.59%)**    |
-| uncheckedAccount2           | 1,233         | 🔴 **+71 (6.11%)**    |
-| uncheckedAccount4           | 1,861         | 🔴 **+145 (8.45%)**   |
-| uncheckedAccount8           | 3,171         | 🔴 **+338 (11.93%)**  |
+| interfaceAccountToken1      | 1,279         | 🔴 **+11 (0.87%)**    |
+| interfaceAccountToken2      | 1,792         | 🟢 **-57 (3.08%)**    |
+| interfaceAccountToken4      | 2,825         | 🟢 **-172 (5.74%)**   |
+| interface1                  | 918           | 🔴 **+40 (4.56%)**    |
+| interface2                  | 1,064         | 🔴 **+41 (4.01%)**    |
+| interface4                  | 1,345         | 🔴 **+44 (3.38%)**    |
+| interface8                  | 1,912         | 🔴 **+45 (2.41%)**    |
+| program1                    | 934           | 🔴 **+44 (4.94%)**    |
+| program2                    | 1,084         | 🔴 **+49 (4.73%)**    |
+| program4                    | 1,373         | 🔴 **+60 (4.57%)**    |
+| program8                    | 1,956         | 🔴 **+77 (4.10%)**    |
+| signer1                     | 923           | 🔴 **+49 (5.61%)**    |
+| signer2                     | 1,272         | 🔴 **+99 (8.44%)**    |
+| signer4                     | 1,957         | 🔴 **+198 (11.26%)**  |
+| signer8                     | 3,332         | 🔴 **+391 (13.29%)**  |
+| systemAccount1              | 945           | 🔴 **+34 (3.73%)**    |
+| systemAccount2              | 1,304         | 🔴 **+69 (5.59%)**    |
+| systemAccount4              | 2,009         | 🔴 **+138 (7.38%)**   |
+| systemAccount8              | 3,424         | 🔴 **+271 (8.59%)**   |
+| uncheckedAccount1           | 931           | 🔴 **+49 (5.56%)**    |
+| uncheckedAccount2           | 1,263         | 🔴 **+101 (8.69%)**   |
+| uncheckedAccount4           | 1,911         | 🔴 **+195 (11.36%)**  |
+| uncheckedAccount8           | 3,207         | 🔴 **+374 (13.20%)**  |
 
 ### Notable changes
 

diff --git a/bench/STACK_MEMORY.md b/bench/STACK_MEMORY.md
@@ -16,8 +16,95 @@ The programs and their tests are located in [/tests/bench](https://github.com/co
 
 Solana version: 2.3.0
 
-| Instruction | Stack Memory | -   |
-| ----------- | ------------ | --- |
+| Instruction                    | Stack Memory | -                   |
+| ------------------------------ | ------------ | ------------------- |
+| account_info1                  | 46           | -                   |
+| account_info2                  | 88           | -                   |
+| account_info4                  | 88           | -                   |
+| account_info8                  | 88           | -                   |
+| account_empty_init1            | 88           | -                   |
+| account_empty_init2            | 88           | -                   |
+| account_empty_init4            | 88           | -                   |
+| account_empty_init8            | 88           | -                   |
+| account_empty1                 | 88           | -                   |
+| account_empty2                 | 88           | -                   |
+| account_empty4                 | 88           | -                   |
+| account_empty8                 | 88           | -                   |
+| account_sized_init1            | 88           | -                   |
+| account_sized_init2            | 88           | -                   |
+| account_sized_init4            | 88           | -                   |
+| account_sized_init8            | 88           | -                   |
+| account_sized1                 | 88           | -                   |
+| account_sized2                 | 88           | -                   |
+| account_sized4                 | 88           | -                   |
+| account_sized8                 | 88           | -                   |
+| account_unsized_init1          | 88           | -                   |
+| account_unsized_init2          | 88           | -                   |
+| account_unsized_init4          | 88           | -                   |
+| account_unsized_init8          | 88           | -                   |
+| account_unsized1               | 88           | -                   |
+| account_unsized2               | 88           | -                   |
+| account_unsized4               | 88           | -                   |
+| account_unsized8               | 88           | -                   |
+| boxed_account_empty_init1      | 88           | -                   |
+| boxed_account_empty_init2      | 88           | -                   |
+| boxed_account_empty_init4      | 88           | -                   |
+| boxed_account_empty_init8      | 88           | -                   |
+| boxed_account_empty1           | 88           | -                   |
+| boxed_account_empty2           | 88           | -                   |
+| boxed_account_empty4           | 88           | -                   |
+| boxed_account_empty8           | 96           | 🔴 **+8 (9.09%)**   |
+| boxed_account_sized_init1      | 88           | -                   |
+| boxed_account_sized_init2      | 88           | -                   |
+| boxed_account_sized_init4      | 88           | -                   |
+| boxed_account_sized_init8      | 88           | -                   |
+| boxed_account_sized1           | 88           | -                   |
+| boxed_account_sized2           | 88           | -                   |
+| boxed_account_sized4           | 88           | -                   |
+| boxed_account_sized8           | 96           | 🔴 **+8 (9.09%)**   |
+| boxed_account_unsized_init1    | 88           | -                   |
+| boxed_account_unsized_init2    | 88           | -                   |
+| boxed_account_unsized_init4    | 88           | -                   |
+| boxed_account_unsized_init8    | 88           | -                   |
+| boxed_account_unsized1         | 88           | -                   |
+| boxed_account_unsized2         | 88           | -                   |
+| boxed_account_unsized4         | 88           | -                   |
+| boxed_account_unsized8         | 96           | 🔴 **+8 (9.09%)**   |
+| boxed_interface_account_mint1  | 88           | -                   |
+| boxed_interface_account_mint2  | 88           | -                   |
+| boxed_interface_account_mint4  | 88           | -                   |
+| boxed_interface_account_mint8  | 96           | 🔴 **+8 (9.09%)**   |
+| boxed_interface_account_token1 | 88           | -                   |
+| boxed_interface_account_token2 | 88           | -                   |
+| boxed_interface_account_token4 | 88           | -                   |
+| boxed_interface_account_token8 | 96           | 🔴 **+8 (9.09%)**   |
+| interface_account_mint1        | 88           | -                   |
+| interface_account_mint2        | 88           | -                   |
+| interface_account_mint4        | 88           | -                   |
+| interface_account_mint8        | 88           | -                   |
+| interface_account_token1       | 104          | 🔴 **+24 (30.00%)** |
+| interface_account_token2       | 104          | 🔴 **+24 (30.00%)** |
+| interface_account_token4       | 104          | 🔴 **+24 (30.00%)** |
+| interface1                     | 88           | -                   |
+| interface2                     | 88           | -                   |
+| interface4                     | 88           | -                   |
+| interface8                     | 88           | -                   |
+| program1                       | 88           | -                   |
+| program2                       | 88           | -                   |
+| program4                       | 88           | -                   |
+| program8                       | 88           | -                   |
+| signer1                        | 88           | -                   |
+| signer2                        | 88           | -                   |
+| signer4                        | 88           | -                   |
+| signer8                        | 88           | -                   |
+| system_account1                | 88           | -                   |
+| system_account2                | 88           | -                   |
+| system_account4                | 88           | -                   |
+| system_account8                | 88           | -                   |
+| unchecked_account1             | 88           | -                   |
+| unchecked_account2             | 88           | -                   |
+| unchecked_account4             | 88           | -                   |
+| unchecked_account8             | 88           | -                   |
 
 ### Notable changes
 

diff --git a/docs/content/docs/references/account-constraints.mdx b/docs/content/docs/references/account-constraints.mdx
@@ -38,6 +38,33 @@ Examples: [Github](https://github.com/solana-developers/anchor-examples/tree/mai
 #[account(mut @ <custom_error>)]
 ```
 
+### `#[account(dup)]`
+
+Description: By default, Anchor will prevents duplicate mutable accounts to avoid potential security issues and unintended behavior. 
+The `dup` constraint explicitly allows this for cases where it's intentional and safe.
+
+**Note**: This constraint only applies to mutable accounts (`mut`). Readonly accounts naturally allow duplicates without requiring the `dup` constraint.
+
+```rust title="attribute"
+#[account(mut, dup)]
+#[account(mut, dup @ <custom_error>)]
+```
+
+```rust title="snippet"
+#[derive(Accounts)]
+pub struct AllowsDuplicateMutable<'info> {
+    #[account(mut)]
+    pub account1: Account<'info, Counter>,
+    // This account can be the same as account1
+    #[account(mut, dup)]
+    pub account2: Account<'info, Counter>,
+}
+
+pub fn allows_duplicate_mutable(ctx: Context<AllowsDuplicateMutable>) -> Result<()> {
+    Ok(())
+}
+```
+
 ### `#[account(init)]`
 
 Description: Creates the account via a CPI to the system program and initializes