APEX: Agent Payment Execution with Policy for Autonomous Agent API Access
Hey there, little explorer! Imagine you have a super-smart toy robot. This robot can ask other toy robots for help, like asking a drawing robot to draw a cat!
Sometimes, asking for help costs a tiny bit of play money. Before, robots used special "crypto coins" to pay. But that was tricky!
Now, a new idea called APEX is like a special piggy bank for your robot. It lets your robot use regular play money, like the coins you use for candy!
This piggy bank also has rules, like "only spend 5 coins today." So your robot doesn't spend all its money at once. It's a clever way for robots to pay for help, safely and easily! Yay robots!
arXiv:2604.02023v1 Announce Type: new Abstract: Autonomous agents are moving beyond simple retrieval tasks to become economic actors that invoke APIs, sequence workflows, and make real-time decisions. As this shift accelerates, API providers need request-level monetization with programmatic spend governance. The HTTP 402 protocol addresses this by treating payment as a first-class protocol event, but most implementations rely on cryptocurrency rails. In many deployment contexts, especially countries with strong real-time fiat systems like UPI, this assumption is misaligned with regulatory and infrastructure realities. We present APEX, an implementation-complete research system that adapts HTTP 402-style payment gating to UPI-like fiat workflows while preserving policy-governed spend contro
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Abstract:Autonomous agents are moving beyond simple retrieval tasks to become economic actors that invoke APIs, sequence workflows, and make real-time decisions. As this shift accelerates, API providers need request-level monetization with programmatic spend governance. The HTTP 402 protocol addresses this by treating payment as a first-class protocol event, but most implementations rely on cryptocurrency rails. In many deployment contexts, especially countries with strong real-time fiat systems like UPI, this assumption is misaligned with regulatory and infrastructure realities. We present APEX, an implementation-complete research system that adapts HTTP 402-style payment gating to UPI-like fiat workflows while preserving policy-governed spend control, tokenized access verification, and replay resistance. We implement a challenge-settle-consume lifecycle with HMAC-signed short-lived tokens, idempotent settlement handling, and policy-aware payment approval. The system uses FastAPI, SQLite, and Python standard libraries, making it transparent, inspectable, and reproducible. We evaluate APEX across three baselines and six scenarios using sample sizes 2-4x larger than initial experiments (N=20-40 per scenario). Results show that policy enforcement reduces total spending by 27.3% while maintaining 52.8% success rate for legitimate requests. Security mechanisms achieve 100% block rate for both replay attacks and invalid tokens with low latency overhead (19.6ms average). Multiple trial runs show low variance across scenarios, demonstrating high reproducibility with 95% confidence intervals. The primary contribution is a controlled agent-payment infrastructure and reference architecture that demonstrates how agentic access monetization can be adapted to fiat systems without discarding security and policy guarantees.
Comments: 13 pages, 4 figures, 8 tables. Includes implementation details, experimental evaluation with statistical analysis, and reproducible results. Code and data available upon request
Subjects:
Cryptography and Security (cs.CR); Artificial Intelligence (cs.AI)
Cite as: arXiv:2604.02023 [cs.CR]
(or arXiv:2604.02023v1 [cs.CR] for this version)
https://doi.org/10.48550/arXiv.2604.02023
arXiv-issued DOI via DataCite (pending registration)
Submission history
From: Mohd Safwan Uddin Mr [view email] [v1] Thu, 2 Apr 2026 13:32:01 UTC (342 KB)
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