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Stable is the first StableChain designed for seamless financial transactions, powered by USDT as the native gas token.
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x402 embeds payments directly into API requests, eliminating the need for accounts, subscriptions, or external billing workflows.
Stable serves as the execution layer for the agentic economy, offering fast finality, a unified gas token, and predictable fees.
Payments are authorized via signatures and executed by facilitators, removing the need for user-side transaction handling
Client-side complexity is minimized: no gas management or manual transaction construction is required.
EIP-3009 enables native signature-based payments for USDT, with Permit2 extending support to any ERC-20 token
Together, x402 and Stable enable a practical foundation for pay-per-use APIs and autonomous payment flows
As automation systems and AI-driven applications increasingly interact with digital services through APIs, data pipelines, and compute infrastructure, the payment rails supporting these interactions remain fundamentally designed for humans. Traditional online payments assume workflows such as:
account creation
login and credential management
payment method registration
subscription billing cycles
This model introduces friction when services must charge per interaction rather than through periodic subscriptions. It also creates barriers for automated systems that need to execute transactions programmatically.
The x402 protocol introduces a new primitive for the web:
x402 embeds payments directly into API requests, eliminating the need for accounts, subscriptions, or external billing workflows.
Stable serves as the execution layer for the agentic economy, offering fast finality, a unified gas token, and predictable fees.
Payments are authorized via signatures and executed by facilitators, removing the need for user-side transaction handling
Client-side complexity is minimized: no gas management or manual transaction construction is required.
EIP-3009 enables native signature-based payments for USDT, with Permit2 extending support to any ERC-20 token
Together, x402 and Stable enable a practical foundation for pay-per-use APIs and autonomous payment flows
As automation systems and AI-driven applications increasingly interact with digital services through APIs, data pipelines, and compute infrastructure, the payment rails supporting these interactions remain fundamentally designed for humans. Traditional online payments assume workflows such as:
account creation
login and credential management
payment method registration
subscription billing cycles
This model introduces friction when services must charge per interaction rather than through periodic subscriptions. It also creates barriers for automated systems that need to execute transactions programmatically.
The x402 protocol introduces a new primitive for the web:
Subscribe to Stable
Stable is the first StableChain designed for seamless financial transactions, powered by USDT as the native gas token.
Share Dialog
While x402 defines the payment interaction pattern, the efficiency of this model depends heavily on the underlying settlement infrastructure. This is where Stable’s architecture becomes important.
The x402 protocol introduces a simple way to integrate payments directly into web requests using the 402 Payment Required status code.
Instead of relying on accounts, API keys, or subscriptions, a service can return a 402 response when a client accesses a paid endpoint, including the required payment details.
In practice, integrating x402 can be as simple as adding a payment middleware to a route, enabling per-request pricing with minimal changes.
The client signs a payment authorization and sends the request again with the payment proof in the header. A facilitator verifies the authorization, submits the transaction on-chain, and once confirmed, the server returns the requested resource.
At a high level, the payment flow with x402 looks like:
Client requests a resource
Server responds with 402 Payment Required
Client signs payment
Request is sent again with signed payment (to Server)
Server forwards signed payment proof to Facilitator
Facilitator verifies and settles on-chain
Resource is returned
This allows services to charge per interaction rather than through subscriptions, and naturally enables agent-to-agent (A2A) and machine-to-machine (M2M) payments.
While x402 enables payments to be embedded directly into web requests, the effectiveness of this model depends on the settlement layer processing those payments.
Running x402 on general-purpose blockchains can introduce additional friction for automated payment flows. Clients often need to manage a separate gas token, construct and broadcast transactions, and deal with fee volatility caused by network congestion. These constraints add complexity to what is intended to be a lightweight request-level payment model.
Stable addresses these constraints by providing a settlement layer optimized specifically for stablecoin transfers and micropayments.
Stable is an EVM-compatible Layer 1 designed around USDT as its native gas and settlement asset, enabling payments to be priced directly in a stable unit of account.
Key architectural properties include:
Stablecoin-native settlement Payments are denominated in USDT, allowing services to price interactions predictably without relying on volatile tokens.
Sub-second finality Stable achieves block finality of approximately 700 milliseconds, enabling near real-time payment verification before a request is fulfilled.
Micropayment economics Stable is optimized for high-throughput stablecoin transfers with transaction costs of ~$0.0001 per transaction, making it viable to charge for individual requests such as API calls or compute usage.
x402 defines the interaction model for agentic payments. Stable defines the settlement layer.
x402 enables payments to be embedded directly into the request flow, removing accounts, subscriptions, and pre-configured billing
Stable enables those payments to be executed efficiently, with low fees, fast finality, and no gas token overhead
Together, these properties make Stable a natural settlement layer for x402-based payments, enabling services to support pay-per-request interactions without the overhead typically associated with blockchain transactions.
A key requirement for request-level payments is minimizing the complexity of executing transactions. If a client must manage gas tokens, estimate fees, or construct transactions manually, the payment flow becomes difficult to integrate directly into application requests.
Stable addresses this through two mechanisms: Gas Waiver infrastructure and signature-based token transfers using EIP-3009.
Gas Waiver Infrastructure
Stable allows governance-approved infrastructure providers, known as waivers, to submit transactions with a gas price of zero.
Waivers are governance-approved addresses that can broadcast transactions with gasPrice = 0.
The client signs an InnerTx with zero gas price.
A waiver service wraps this transaction into a WrapperTx and broadcasts it to a designated marker address on the network.
This architecture removes the need for clients to manage gas tokens or estimate transaction fees. For automated systems interacting with services through x402, the client only needs to hold USDT.
Signature-Based Payments with EIP-3009 and Permit2
Stable’s USDT0 contract natively implements EIP-3009 (transferWithAuthorization), enabling token transfers through signed authorizations.
Instead of constructing and broadcasting a transaction, the client simply signs a transfer authorization off-chain.
x402 on Stable supports two signature-based payment paths:
EIP-3009 (default): Native to Stable's USDT contract. The client signs a transfer authorization off-chain, the facilitator verifies and settles on-chain. No gas token required.
Permit2: For ERC-20 tokens that do not support native signature-based transfers. The facilitator sponsors the gas and handles approval and settlement atomically via the ERC-20 Approval Gas Sponsoring extension.
EIP-3009 flow:
the client signs a transfer authorization specifying the payment amount and recipient
the signed authorization is included with the request
a payment facilitator verifies the signed authorization and submits the settlement transaction on-chain
Permit2 flow:
The server advertises erc20ApprovalGasSponsoring in the PaymentRequired response
The client checks if Permit2 allowance is sufficient; if not, signs a raw approve(Permit2, MaxUint256)transaction off-chain without broadcasting it
The signed approval is included with the request
The facilitator executes an atomic batch, broadcasting the approval and settling the payment together, with no window for front-running
Both flows remove the need for users to manage gas or submit transactions directly.
EIP-3009 is the preferred path for USDT on Stable.
Permit2 is the universal fallback for any ERC-20.
By combining signature-based transfers with gas sponsorship, Stable enables seamless, low-friction payments with minimal client-side logic.
Supporting Infrastructure
Several infrastructure components support x402-based payments on Stable, enabling developers and automated clients to integrate request-level payments without directly managing blockchain interactions.
Semantic Pay
Semantic Pay operates an x402-compatible payment facilitator for the Stable network.
Its role includes:
verifying signed payment authorizations
submitting settlement transactions to the Stable chain
preventing replay or spam attacks during payment verification.
Because the facilitator handles on-chain submission and monitoring, services integrating x402 do not need to run their own blockchain infrastructure or track transaction confirmations themselves.
Heurist
Heurist operates as an x402-compatible payment facilitator within the Stable ecosystem.
Its role includes:
verifying signed payment authorizations
submitting settlement transactions to the Stable chain
preventing replay or invalid transactions during payment verification
ensuring reliable execution of request-level payments across services
Heurist contributes to expanding the facilitator layer on Stable, improving reliability, redundancy, and scalability for agentic payment flows.
Wallet Development Kit (WDK)
Tether’s Wallet Development Kit (WDK) enables applications to create and manage self-custodial wallets that can interact programmatically with payment systems.
WDK allows clients to:
generate and store private keys locally
sign payment authorizations programmatically
integrate directly with x402-compatible payment flows.
Because WDK wallets satisfy the signer interface required by the x402 SDK, clients can automatically detect 402 Payment Required responses, sign the required authorization, and complete the request.
Supporting Protocols
In automated service environments, payments often operate alongside other protocols that enable coordination between clients and services.
Examples include:
XMTP, which provides encrypted communication between wallet identities.
ERC-8004, which introduces registries for agent identity, reputation, and validation.
Together with x402, these components allow systems to discover services, coordinate interactions, and execute payments within a programmable infrastructure.
Execution Properties of Stable
Stablecoin-native settlement: Payments are denominated in USDT, allowing services to price interactions in a stable unit of account.
No gas token dependency: Through Gas Waiver infrastructure, transactions can be submitted without requiring clients to hold or manage a separate gas token.
Signature-based payments: USDT0 implements EIP-3009 (transferWithAuthorization), allowing payments to be executed through signed authorizations rather than manually constructed transactions.
Fast settlement: Stable achieves ~700ms block finality, enabling quick payment verification.
Micropayment economics: Transaction costs around $0.0001 make request-level pricing economically viable.
Together, these properties allow x402 payments on Stable to function as lightweight, request-level transactions without the overhead typically associated with blockchain payments.
Conclusion
The x402 protocol introduces a simple mechanism for embedding payments directly into the request layer of the web, enabling services to charge for individual interactions without relying on accounts or subscription billing.
For this model to function efficiently, the underlying settlement layer must support fast confirmation, predictable costs, and minimal client-side complexity.
Stable provides these capabilities through its stablecoin-native architecture, gasless transaction infrastructure, signature-based payment flows, and sub-second settlement. Together, these properties allow x402 payments to operate as lightweight, request-level transactions that can be integrated directly into application workflows.
As payment models move toward pay-per-use digital services, infrastructure optimized for high-frequency, low-cost transactions becomes increasingly important. Stable provides a settlement layer designed to support these interactions.
Build on Stable
Documentation: https://docs.stable.xyz
Mainnet Hub: https://hub.stable.xyz
Blog: https://blog.stable.xyz
X: @Stable
Community: https://discord.gg/stablexyz
While x402 defines the payment interaction pattern, the efficiency of this model depends heavily on the underlying settlement infrastructure. This is where Stable’s architecture becomes important.
The x402 protocol introduces a simple way to integrate payments directly into web requests using the 402 Payment Required status code.
Instead of relying on accounts, API keys, or subscriptions, a service can return a 402 response when a client accesses a paid endpoint, including the required payment details.
In practice, integrating x402 can be as simple as adding a payment middleware to a route, enabling per-request pricing with minimal changes.
The client signs a payment authorization and sends the request again with the payment proof in the header. A facilitator verifies the authorization, submits the transaction on-chain, and once confirmed, the server returns the requested resource.
At a high level, the payment flow with x402 looks like:
Client requests a resource
Server responds with 402 Payment Required
Client signs payment
Request is sent again with signed payment (to Server)
Server forwards signed payment proof to Facilitator
Facilitator verifies and settles on-chain
Resource is returned
This allows services to charge per interaction rather than through subscriptions, and naturally enables agent-to-agent (A2A) and machine-to-machine (M2M) payments.
While x402 enables payments to be embedded directly into web requests, the effectiveness of this model depends on the settlement layer processing those payments.
Running x402 on general-purpose blockchains can introduce additional friction for automated payment flows. Clients often need to manage a separate gas token, construct and broadcast transactions, and deal with fee volatility caused by network congestion. These constraints add complexity to what is intended to be a lightweight request-level payment model.
Stable addresses these constraints by providing a settlement layer optimized specifically for stablecoin transfers and micropayments.
Stable is an EVM-compatible Layer 1 designed around USDT as its native gas and settlement asset, enabling payments to be priced directly in a stable unit of account.
Key architectural properties include:
Stablecoin-native settlement Payments are denominated in USDT, allowing services to price interactions predictably without relying on volatile tokens.
Sub-second finality Stable achieves block finality of approximately 700 milliseconds, enabling near real-time payment verification before a request is fulfilled.
Micropayment economics Stable is optimized for high-throughput stablecoin transfers with transaction costs of ~$0.0001 per transaction, making it viable to charge for individual requests such as API calls or compute usage.
x402 defines the interaction model for agentic payments. Stable defines the settlement layer.
x402 enables payments to be embedded directly into the request flow, removing accounts, subscriptions, and pre-configured billing
Stable enables those payments to be executed efficiently, with low fees, fast finality, and no gas token overhead
Together, these properties make Stable a natural settlement layer for x402-based payments, enabling services to support pay-per-request interactions without the overhead typically associated with blockchain transactions.
A key requirement for request-level payments is minimizing the complexity of executing transactions. If a client must manage gas tokens, estimate fees, or construct transactions manually, the payment flow becomes difficult to integrate directly into application requests.
Stable addresses this through two mechanisms: Gas Waiver infrastructure and signature-based token transfers using EIP-3009.
Gas Waiver Infrastructure
Stable allows governance-approved infrastructure providers, known as waivers, to submit transactions with a gas price of zero.
Waivers are governance-approved addresses that can broadcast transactions with gasPrice = 0.
The client signs an InnerTx with zero gas price.
A waiver service wraps this transaction into a WrapperTx and broadcasts it to a designated marker address on the network.
This architecture removes the need for clients to manage gas tokens or estimate transaction fees. For automated systems interacting with services through x402, the client only needs to hold USDT.
Signature-Based Payments with EIP-3009 and Permit2
Stable’s USDT0 contract natively implements EIP-3009 (transferWithAuthorization), enabling token transfers through signed authorizations.
Instead of constructing and broadcasting a transaction, the client simply signs a transfer authorization off-chain.
x402 on Stable supports two signature-based payment paths:
EIP-3009 (default): Native to Stable's USDT contract. The client signs a transfer authorization off-chain, the facilitator verifies and settles on-chain. No gas token required.
Permit2: For ERC-20 tokens that do not support native signature-based transfers. The facilitator sponsors the gas and handles approval and settlement atomically via the ERC-20 Approval Gas Sponsoring extension.
EIP-3009 flow:
the client signs a transfer authorization specifying the payment amount and recipient
the signed authorization is included with the request
a payment facilitator verifies the signed authorization and submits the settlement transaction on-chain
Permit2 flow:
The server advertises erc20ApprovalGasSponsoring in the PaymentRequired response
The client checks if Permit2 allowance is sufficient; if not, signs a raw approve(Permit2, MaxUint256)transaction off-chain without broadcasting it
The signed approval is included with the request
The facilitator executes an atomic batch, broadcasting the approval and settling the payment together, with no window for front-running
Both flows remove the need for users to manage gas or submit transactions directly.
EIP-3009 is the preferred path for USDT on Stable.
Permit2 is the universal fallback for any ERC-20.
By combining signature-based transfers with gas sponsorship, Stable enables seamless, low-friction payments with minimal client-side logic.
Supporting Infrastructure
Several infrastructure components support x402-based payments on Stable, enabling developers and automated clients to integrate request-level payments without directly managing blockchain interactions.
Semantic Pay
Semantic Pay operates an x402-compatible payment facilitator for the Stable network.
Its role includes:
verifying signed payment authorizations
submitting settlement transactions to the Stable chain
preventing replay or spam attacks during payment verification.
Because the facilitator handles on-chain submission and monitoring, services integrating x402 do not need to run their own blockchain infrastructure or track transaction confirmations themselves.
Heurist
Heurist operates as an x402-compatible payment facilitator within the Stable ecosystem.
Its role includes:
verifying signed payment authorizations
submitting settlement transactions to the Stable chain
preventing replay or invalid transactions during payment verification
ensuring reliable execution of request-level payments across services
Heurist contributes to expanding the facilitator layer on Stable, improving reliability, redundancy, and scalability for agentic payment flows.
Wallet Development Kit (WDK)
Tether’s Wallet Development Kit (WDK) enables applications to create and manage self-custodial wallets that can interact programmatically with payment systems.
WDK allows clients to:
generate and store private keys locally
sign payment authorizations programmatically
integrate directly with x402-compatible payment flows.
Because WDK wallets satisfy the signer interface required by the x402 SDK, clients can automatically detect 402 Payment Required responses, sign the required authorization, and complete the request.
Supporting Protocols
In automated service environments, payments often operate alongside other protocols that enable coordination between clients and services.
Examples include:
XMTP, which provides encrypted communication between wallet identities.
ERC-8004, which introduces registries for agent identity, reputation, and validation.
Together with x402, these components allow systems to discover services, coordinate interactions, and execute payments within a programmable infrastructure.
Execution Properties of Stable
Stablecoin-native settlement: Payments are denominated in USDT, allowing services to price interactions in a stable unit of account.
No gas token dependency: Through Gas Waiver infrastructure, transactions can be submitted without requiring clients to hold or manage a separate gas token.
Signature-based payments: USDT0 implements EIP-3009 (transferWithAuthorization), allowing payments to be executed through signed authorizations rather than manually constructed transactions.
Fast settlement: Stable achieves ~700ms block finality, enabling quick payment verification.
Micropayment economics: Transaction costs around $0.0001 make request-level pricing economically viable.
Together, these properties allow x402 payments on Stable to function as lightweight, request-level transactions without the overhead typically associated with blockchain payments.
Conclusion
The x402 protocol introduces a simple mechanism for embedding payments directly into the request layer of the web, enabling services to charge for individual interactions without relying on accounts or subscription billing.
For this model to function efficiently, the underlying settlement layer must support fast confirmation, predictable costs, and minimal client-side complexity.
Stable provides these capabilities through its stablecoin-native architecture, gasless transaction infrastructure, signature-based payment flows, and sub-second settlement. Together, these properties allow x402 payments to operate as lightweight, request-level transactions that can be integrated directly into application workflows.
As payment models move toward pay-per-use digital services, infrastructure optimized for high-frequency, low-cost transactions becomes increasingly important. Stable provides a settlement layer designed to support these interactions.
Build on Stable
Documentation: https://docs.stable.xyz
Mainnet Hub: https://hub.stable.xyz
Blog: https://blog.stable.xyz
X: @Stable
Community: https://discord.gg/stablexyz
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