The choice of stablecoin determines the cost, performance, custody model, and long-term viability of an x402 deployment. This page compares the two options available today and explains why Semantic builds on USD₮.
Market position
USD₮ holds roughly 60% of the stablecoin market ($186B market cap) with daily trading volume 5× that of USDC ($40–200B vs $5–40B). It’s the default unit of account across global exchanges, P2P markets, and cross-border corridors. For x402, this means building on USD₮ gives agents access to the deepest liquidity and broadest acceptance available.
| Metric | USD₮ | USDC |
|---|
| Market cap (Q3 2025) | ≈$186B | ≈$75B |
| Market share | ≈60% | ≈25% |
| Daily trading volume | $40–200B | $5–40B |
| Active users | 350M+ | Not disclosed |
| Blockchain presence | 20+ chains | 15+ chains |
| Primary corridors | Global, EM-heavy | US/EU |
Settlement infrastructure
x402 payments settle on-chain. The choice of network directly affects finality speed, transaction cost, and fee predictability.
CDP facilitator (USDC on Base and Solana)
Coinbase’s CDP facilitator currently offers a free tier of 1,000 transactions per month, after which each transaction costs $0.001. The facilitator absorbs gas fees on the buyer’s behalf.
This works for prototyping, but raises questions at scale. Coinbase subsidizes gas today, but subsidies have a known trajectory: attract usage, then reprice once lock-in occurs. Base and Solana are general-purpose chains where fees fluctuate with network demand, and gas must be paid in volatile tokens (ETH, SOL), adding operational complexity for agents that otherwise only need to manage stablecoins.
Semantic facilitator (USD₮ on Plasma and Stable)
Semantic settles on Plasma and Stable: Layer 1 chains purpose-built for USD₮ transactions.
Both chains share a design principle. Stablecoin transfers are the primary workload, not an afterthought. This means:
- Near-zero-fee USD₮ transfers. are a protocol-level feature, not a temporary subsidy. The chains are economically designed around this use case.
- No gas token friction. Agents hold USD₮ and pay in USD₮ (or pay nothing at all for simple transfers).
- Sub-second finality. Enables real-time settlement for high-frequency agent interactions.
- Predictable costs. Because these chains are optimized for stablecoin throughput rather than general computation, fee behavior is more stable and less susceptible to congestion spikes from unrelated workloads.
Wallet custody
x402 requires wallets on both sides of every payment. How those wallets manage private keys determines who actually controls the funds.
CDP Server Wallets
Coinbase’s CDP Server Wallets store private keys inside Trusted Execution Environments (TEEs) on Coinbase infrastructure. All wallet operations, creation, signing, management, happen through Coinbase’s API.
This means:
- Keys live on Coinbase infrastructure. The keys depend on Coinbase’s infrastructure being available and uncompromised.
- API dependency. Every wallet operation requires a network call to Coinbase’s API.
- Platform coupling. Wallets created through CDP exist within the CDP ecosystem.
WDK (Wallet Development Kit) by Tether
Semantic integrates seamlessly with WDK, an open-source wallet toolkit for self-custodial wallets. WDK generates and stores private keys locally. Keys never leave the local environment.
This means:
- True self-custody. No third party can freeze, seize, or block an agent’s funds. The agent (or its operator) has sole control.
- No infrastructure dependency. WDK is an OS library, not a service. Wallets work offline for signing operations. No API calls to any third party.
- Runs anywhere. Desktop, server, mobile, embedded, same library, same keys, same behavior.
| CDP Server Wallets | WDK |
|---|
| Key storage | Coinbase TEE | Local (device/server/agent) |
| Key access | Via Coinbase API | Direct, local |
| Infrastructure dependency | Coinbase API must be available | None (library) |
| Open source | No | Yes |
| Vendor lock-in | CDP ecosystem | None (BIP standard derivation) |
| Freeze/seize risk | Subject to Coinbase policies | None |
The path to trustless infrastructure
Semantic’s choice of USD₮, purpose-built chains, and self-custodial wallets is part of a broader architectural direction.
Today, x402 facilitators, including Semantic’s, are centralized services. A server trusts the facilitator to verify and settle honestly. This works, and it’s the practical starting point for any payment infrastructure. But it’s not the end state.
Semantic will integrate with QVAC as an agent runtime and Hyperswarm as a transport layer, replacing HTTP servers with direct peer-to-peer transactions. Combined with self-custodial WDK wallets and on-chain settlement, this removes every centralized dependency from the payment flow: discovery, inference, signing, and settlement all happen without a third party.
The vision is a fully peer-to-peer, trustless, permissionless agentic economy. Last modified on February 20, 2026
