> ## Documentation Index
> Fetch the complete documentation index at: https://docs.polygon.technology/llms.txt
> Use this file to discover all available pages before exploring further.

# Smart Sessions: Technical Deep Dive

> How implicit and explicit sessions work under the hood, their security guarantees, and how to combine them for payment flows.

Smart Sessions solve the core UX problem in wallet-based apps: every transaction requiring a user approval prompt. For payment products, this creates unacceptable friction. Smart Sessions replace per-transaction approvals with a scoped, time-limited permission grant enforced onchain.

See the [Smart Sessions](/wallets/smart-sessions) page for integration code and configuration examples.

## Two types of Smart Sessions

Sequence offers two distinct session types, each designed for a different purpose:

* **Implicit Sessions**: maximum convenience within a single, trusted app.
* **Explicit Sessions**: granular, user-approved control over any onchain action.

***

## Implicit Sessions

An Implicit Session is the simplest and most common type. Its purpose is to make the experience inside a single app as smooth as possible: zero approval prompts, gas sponsored by the app.

### How it works

1. The user connects their wallet to your app (e.g., `app.yourproduct.com`).
2. A session is automatically created, cryptographically locked to that specific domain, with no user approval required.
3. The user can perform any action inside that app without further prompts.

### Security guardrail

If the app attempts to use this session to call a contract outside its domain, such as calling the USDC contract directly, the transaction is automatically rejected onchain. The session is only valid for the app's own smart contracts.

<Warning>
  All transactions must be sponsored by the app when using Implicit Sessions. Using any other currency as a fee option is treated as an external contract interaction and will be blocked.
</Warning>

### At a glance

| Aspect     | Details                                                       |
| ---------- | ------------------------------------------------------------- |
| Best for   | Day-to-day use within a fully gas-sponsored app, zero prompts |
| Constraint | Cannot interact with any external smart contract              |
| Gas        | App must sponsor all gas                                      |

***

## Explicit Sessions

An Explicit Session is designed for when an app needs to perform specific tasks that interact with external protocols: stablecoin transfers, DeFi interactions, or any flow where the user should review and approve a defined scope.

### How it works

1. The app presents the wallet with a list of specific permissions it needs: which contract, which method, maximum amount, expiry.
2. The wallet displays these rules in a human-readable format for the user to review and approve.
3. The app can then execute those actions automatically without further prompts.

### Security guardrail

Each rule is validated onchain. If the app attempts anything outside the approved scope, such as spending 101 USDC instead of 100, calling `approve` instead of `transfer`, or targeting a different address, the transaction fails at the contract level.

### At a glance

| Aspect     | Details                                                                  |
| ---------- | ------------------------------------------------------------------------ |
| Best for   | External contract interactions, stablecoin transfers, recurring payments |
| Constraint | Requires one upfront user approval                                       |
| Gas        | User or app can pay                                                      |

***

## Combining session types

Most payment products use both session types together:

1. **Implicit session** for in-app UI interactions: status checks, balance reads, small in-app transfers within your own contracts.
2. **Explicit session** for external transfers or protocol interactions that require user-scoped approval.

When an Implicit Session goes out of scope, Sequence SDKs automatically fall back to a single-transaction approval. For repeated out-of-scope actions, request an Explicit Session to restore uninterrupted execution.

## Onchain enforcement

Smart Session rules are part of the wallet's [Merkleized configuration](/wallets/wallet-configuration). They are cryptographically verifiable without trusting any off-chain service. Transactions that exceed the defined scope are rejected at the contract level; your app cannot exceed what the user approved, even accidentally.