Overview

Fast Skill is complete payment infrastructure designed for AI agents. Its payment stack consists of three integrated layers shown below:

These docs are intentionally high-level. The implementation source of truth lives in the Fast SDK monorepo on GitHub, which contains the SDKs, shared packages, and CLI used across the Fast developer stack.

The monorepo currently includes seven core packages:

Package	Role	GitHub
@fastxyz/sdk	Core Fast network SDK for signing, submission, and queries	packages/fast-sdk
@fastxyz/allset-sdk	Cross-network settlement and bridging through AllSet	packages/allset-sdk
@fastxyz/x402-client	Client-side support for x402-paid HTTP requests	packages/x402-client
@fastxyz/x402-server	Server-side middleware for x402-protected routes	packages/x402-server
@fastxyz/x402-facilitator	Verification and settlement service for x402 flows	packages/x402-facilitator
@fastxyz/fast-schema	Shared schemas and codecs for Fast APIs and payloads	packages/fast-schema
@fastxyz/x402-types	Shared protocol types and helpers for x402	packages/x402-types

The same monorepo also includes the Fast CLI, which exposes account, funding, transfer, and x402 payment workflows from the terminal.

                        FAST SKILL PAYMENT STACK

 +-----------------------------------+  +-------------------------------+
 |    Payment Protocol Adapters      |  |     Funding Abstraction       |
 |    Entity <-> Entity Agreement    |  |   Fiat <-> Crypto Agreement   |
 |                                   |  |                               |
 |  +-------+  +-------+  +-------+  |  |  +--------+ +-------+ +-----+ |
 |  | x402  |  |  ACP  |  |Stripe |  |  |  | Credit | |Stable-| |Bank | |
 |  +-------+  +-------+  +-------+  |  |  |  Card  | | coins | |Xfer | |
 |                                   |  |  +--------+ +-------+ +-----+ |
 +-----------------+-----------------+  +---------------+---------------+
                   |                                    |
                  API                            On/Off ramping
                   |                                    |
                   v                                    v
 +---------------------------------------------------------------------+
 |                                                                     |
 |                       Core SDK Execution                            |
 |                  Account <-> Account Agreement                      |
 |                                                                     |
 |   +---------------------+     +---------------------------+         |
 |   |      Fast SDK       |     |        AllSet SDK         |         |
 |   |   Fast <-> Fast     |     | Fast/Chain <-> Fast/Chain |         |
 |   +----------+----------+     +-------------+-------------+         |
 |              |                              |                       |
 |              v                              v                       |
 |   +-----------------------------------------------------+           |
 |   |                   FAST network                      |           |
 |   +-----------------------------------------------------+           |
 |                                                                     |
 +---------------------------------------------------------------------+

Core SDK Execution

The foundation layer handles account-to-account operations on the Fast network: • Fast SDK — Native Fast-to-Fast transfers with sub-second settlement • AllSet SDK — Seamless movement between Fast and external networks (Base, Arbitrum, Ethereum, etc.) without bridging complexity

Payment Protocol Adapters

Entity-to-entity payment protocols that standardize how agents request and send payments: • x402 — HTTP-native payment protocol (pay-per-API-call) • ACP — Agent Communication Protocol for agent-to-agent commerce • Stripe — Traditional payment rails integration

Funding Abstraction

Simplifies how money enters and exits the system: • Credit card on-ramps • Stablecoin deposits • Bank transfers

The SDK exposes these layers through three composable primitives — FastProvider, Signer, and TransactionBuilder — that handle serialization, signing, and network communication automatically. For installation details, runnable examples, and package-level APIs, see the Fast SDK monorepo on GitHub.