Alchemy's agent pitch is right: don't put a private key in a prompt or a .env; grant scoped, time-bound session keys instead. Its implementation is an ERC-4337 smart account, which means it is EVM-only. On Solana, Alchemy offers gas sponsorship and no smart accounts, bundler, or session keys.
Alchemy session keys for the EVM side of a multichain agent; Coldstar for its Solana side.
| Coldstar | Alchemy Smart Wallets | |
|---|---|---|
| Who holds the root key | You. The cold root lives encrypted on your own USB drive. No vendor holds a key, a share, or an account. | Owner key is bring-your-own or a hosted embedded signer (historically Turnkey enclaves). Permissions live in the on-chain ERC-4337 account. |
| Where the key lives | On your machine. The air-gapped root signs a bounded policy envelope; a disposable session key signs routine transactions inside it. | External signer or TEE for the owner; permissions on-chain (Modular Account v2). EVM. |
| Policy engine | Per-transaction limit, daily cap, program allowlist, recipient allowlist and blocklist, escalate-above threshold — for SOL and per SPL token, with per-mint limits in base units and destinations checked against the recipients' token accounts. Token instructions that cannot be bounded, Approve above all, escalate to a human rather than signing. Evaluated locally, first match wins, before any signature exists. The daily cap can be read back from the chain, so deleting the local ledger cannot reset it, and an allowlisted program's real debit can be measured by simulation rather than trusted. | Session keys: native transfer limit, ERC-20 cumulative allowance, gas limit, contract and function-selector allowlists, expiry. Validated on-chain. EVM only. |
| Out-of-policy transactions | ESCALATE to a human over air-gapped QR, or REJECT. No signature is produced for a rejected transaction. A grant can also be revoked on-chain before it expires, by the root or by a hot revoker key that cannot spend; the signer refuses everything from then on, and a chain it cannot reach escalates rather than signs. | Reverted on-chain; sessions revocable from the dashboard. |
| Cold / offline root | Yes — the root key never touches a networked machine. It signs a policy envelope offline; the online signer verifies that signature and refuses to start if the policy was edited, the session key is not the one named, or the grant expired. | Owner can be a hardware wallet in principle; no documented cold-root workflow. |
| Agent integration | Framework-agnostic: the agent proposes an unsigned transaction, the signer decides. ColdstarWallet is an open-source drop-in for Solana Agent Kit's BaseWallet, and coldstar-signer-mcp exposes the same policy-gated wallet to any MCP client. Squads spending limits are decoded rather than trusted, so an agent can be a vault member bounded by the chain and by local policy. | Agents page: scoped, time-bound permissions; CLI scoped sessions. |
| Solana support | Solana mainnet. Core is chain-agnostic; EVM signing exists. | Partial. Solana: gas sponsorship yes; bundler, smart accounts, and session keys no. |
| Source & self-hosting | Open source (MIT), self-hosted. No API key, no SaaS dependency, nothing to go down. | aa-sdk MIT (EVM/viem). Hosted APIs. |
| Pricing | Free software plus a ~$10 drive. | Compute units per call (e.g. prepareCalls 1,750 CU, sendPreparedCalls 3,000 CU); plan tiers vary. |
| Maturity | Beta — the signing core and policy engine are in scope for the planned independent audit. | Production; a leading EVM account-abstraction stack. |
If you are on EVM, Alchemy's session keys are a strong answer and Coldstar's EVM support is secondary. If you are on Solana, this page exists to save you a search: Alchemy's smart wallets do not run there.
Alchemy's model anchors permissions in an on-chain smart account: the session key can only do what the account's validation logic allows, and anyone can verify that. The owner signer is yours or a hosted enclave. This is a good design for EVM agents and it simply does not exist on Solana, where Alchemy's supported-chains table lists gas sponsorship only.
Coldstar's model is off-chain but local: a cold root signs a policy envelope; a session key acts inside it under a rule list enforced before signing. It works on Solana today and has secondary EVM support.
Alchemy is production. Coldstar is beta, pre-audit.
No. At review time Alchemy's supported-chains table showed Solana with gas sponsorship only: no smart accounts, no bundler, no session keys.
Coldstar's core is chain-agnostic and EVM signing exists, but Solana is the first-class chain. For an EVM-only agent, Alchemy's session keys are the more mature option.
The policy envelope: the offline root authorises a disposable session key bounded by limits, allowlists, and a daily cap, enforced locally rather than on-chain.
Open source, MIT. macOS, Linux, Windows — and on the Solana Seeker dApp Store.
pip install coldstar
Third-party facts were checked against the vendor's own pages on the date above. Pricing and feature sets change; if something here is out of date, tell us and we will fix it.