Current limitations - Arcium Docs

Keep callback transactions within the size limit

Solana limits a serialized transaction to 1,232 bytes. Callback output shares this limit with signatures, account keys, instructions, and other callback data, so the usable output size depends on the callback. If Arx cannot build the callback as a single transaction, the computation fails with OutputTooLarge. Keep outputs compact and test the largest expected output with the callback accounts used by your application. Split larger results across separate computations when necessary.

Arcis language constraints

Arcis compiles Rust-like code into fixed MPC circuits. The circuit shape must be known at compile time, so several standard Rust patterns need different implementations:

Pattern	Status	Use instead
`Vec`, `String`, `HashMap`	Not supported	Fixed-size arrays, byte arrays, or structs
`while`, `loop`	Not supported	`for` loops with fixed bounds
`break`, `continue`, early `return`	Not supported	A single exit path with conditional assignments
`let ... else`	Not supported	`if let` or `match`
`.reveal()` or `.from_arcis()` inside non-constant conditionals	Not supported	Move the reveal or conversion outside the branch

Arcis supports if, else, else if, if let, let chains, match, matches!, fixed-size arrays, structs, tuples, enums, Option<T>, and fixed-bound loops. Enums and Option<T> cannot be the input or output of an encrypted instruction, and enum discriminants cannot be set explicitly. See the Operations guide for the complete support matrix.

Common errors

Error or symptom	Likely cause	Fix
`OutputTooLarge`	The complete callback transaction exceeds Solana’s transaction size limit	Return less data or split the result across separate computations
Computation never finalizes	Computation definition was not initialized, callback is missing, or cluster configuration is wrong	Initialize the computation definition, check callback registration, and verify the cluster offset
Decryption fails	Nonce mismatch, nonce reuse, wrong MXE key, or incorrect ciphertext order	Use a fresh 16-byte nonce per encryption and match the circuit argument order exactly
Shared input fails silently	Missing `x25519_pubkey` before the nonce and ciphertext	For `Enc<Shared, T>`, pass public key, nonce, then ciphertexts
Callback runs but state is unchanged	Callback account was not writable or was omitted from callback accounts	Mark the account writable in both the callback account list and the Anchor account struct
Circuit compile failure	Unsupported Rust construct or variable-size data	Replace dynamic constructs with fixed-size Arcis patterns

What’s next?

Best practices

Performance tips and common patterns

Operations guide

Complete operation support matrix

Types reference

Supported and unsupported types

Deployment

Deploy your MXE to the network

​Keep callback transactions within the size limit

​Arcis language constraints

​Common errors

​What’s next?