Backend Engineer - AI Inference Systems · Crypto Infrastructure · Traditional Payments
LLM inference & serving (vLLM) · ML systems · Liquid staking · Card & settlement rails · Cross-border payments
Backend engineer specializing in the intersection of crypto infrastructure and traditional payments - systems where on-chain state must reconcile with real-world money movement to the cent.
My work spans both sides of that seam: founding-team engineer at a liquid-staking protocol that scaled past $500M+ in staked assets, four years on cross-border payments and the stablecoin initiative at Visa, and now card and vault products at ether.fi - a non-custodial Visa crypto card built on liquid-restaking infrastructure.
- Currently: Senior Backend Engineer at ether.fi - Cash (card) & Vault products
- Core stack: Go, Rust, Solidity, TypeScript, Java/Spring, Ethereum/EVM, EigenLayer, Kafka, PostgreSQL, Redis
- Education: B.Tech, Computer Science - Delhi College of Engineering (now Delhi Technological University)
- Focus areas: AI inference & serving infrastructure (vLLM), ML systems, decentralized / distributed ML training (DiLoCo), liquid staking & restaking, card settlement, cross-border payments, stablecoins
- Open source: active contributor to AI inference & blockchain infrastructure - merged into vLLM, SGLang, AIBrix, llguidance, Optimism and mcp-go, with further merged fixes in Meilisearch, revm, celestia-node and ethrex
2026 – Present
Building ether.fi Cash, a non-custodial Visa crypto card on liquid-restaking infrastructure where users spend ETH/USDC while their assets continue earning restaking yield.
- Own real-time settlement bridging Visa rails and on-chain vaults (authorization, capture, reconciliation).
- Built the Borrow Mode backend - USDC borrowing against eETH collateral via lending-pool integration.
- Designed an event-driven cashback pipeline (wETH rewards) on Kafka.
- Hardened KYC/AML and risk monitoring with chain-analytics providers; extended multi-chain support across Ethereum L1 and L2s.
Go · Solidity · Ethereum · EigenLayer · Kafka · PostgreSQL · Redis
2022 – 2026
Worked across traditional cross-border payments and Visa's stablecoin / crypto initiative - the bridge between card networks and digital assets.
- Led an 8-engineer team on a real-time payments platform (monolith plus eight microservices) sustaining 2,000+ TPS at 99.98% uptime.
- Delivered Treasury as a Service for the APAC hub - 15 currencies, clients in 60+ countries, powering roughly 80% of APAC liquidity flows through Visa Direct A2A.
- Built the Network Validations Framework - configurable payer/beneficiary identity checks across 100+ SWIFT message types.
- Prototyped on-chain payment settlement in Solidity and Solana as part of the crypto/stablecoin track.
Java · Spring Boot · Solidity · Rust · RabbitMQ · Hazelcast · Docker · Kubernetes
2021 – 2022
Joined as an intern during the final years of my degree at Delhi College of Engineering and grew into a founding member of a ~7-person team building a multi-chain liquid-staking protocol.
- Built Rust / CosmWasm smart contracts powering liquidity pools that scaled past $500M+ in staked assets across multiple chains.
- Led gas-fee analysis and optimization - benchmarking storage and swap costs on Terra/CosmWasm to keep contract execution economical at scale.
- Built a validator analytics platform monitoring 1M+ nodes (React, MongoDB, Ethereum APIs) and APR dashboards.
- Designed cross-chain architecture and on-chain/off-chain synchronization pipelines.
Rust · CosmWasm · TypeScript · Python · React · MongoDB
Research
StragglerPolicy: Straggler-Aware Elastic Membership for Decentralized Training (Zenodo, 2026) - a zero-GPU discrete-event simulator of DiLoCo-style decentralized ML training plus a straggler-aware membership policy for slow-but-alive nodes that existing decentralized-training stacks don't handle. 4.59× faster than the baseline on a persistent-straggler scenario, validated against a torch.distributed/gloo DiLoCo loop. Paper · Code - pjdurden/churn
Upstream contributions - merged fixes in widely-used open-source infrastructure:
| Project | Contribution |
|---|---|
| Optimism | The OP Stack monorepo powering Ethereum L2s (Base, OP Mainnet) - fixed an op-wheel metrics bug that wrote block gas twice and left the base-fee gauge unset (#21127). |
| mcp-go | The leading Go implementation of the Model Context Protocol (MCP) - fixed getServerMetadata returning (nil, nil) instead of an error, closing a silent-failure path in OAuth discovery (#904). |
| vLLM | The standard high-throughput LLM inference & serving engine - build-correctness fix in the precompiled-flag test suite (#44942). |
| SGLang | High-throughput LLM/VLM serving engine - fixed the prefill/decode router's cache-aware routing keying chat requests on the first message only; routing on the full conversation lifted KV-cache hits from ~69% to ~96% and output throughput from ~678 to ~1078 TPS (#27430). |
| AIBrix | The vLLM project's Kubernetes-native LLM-serving control plane - fixed the ZMQ KV-event decoder dropping group_idx/medium/lora_name from vLLM's BlockStored event, which caused false prefix-cache matches on hybrid-attention models (#2384). |
| llguidance | The constrained-decoding engine behind structured / JSON-Schema output in vLLM, SGLang and llama.cpp - fixed multipleOf rejecting negative multiples (#357) and made max_tokens=0 rules compile to the empty string (#356). |
| Meilisearch | Rust search engine (58K★) - fixed a ranking-rules ordering bug that silently dropped matching hits (#6437). |
| revm | The Rust EVM behind Foundry & reth - removed a const-eval panic path in the stack interpreter (#3735). |
| celestia-node | The Go node for the Celestia data-availability layer - unified the header TestSuite constructors behind functional options (#5041). |
| ethrex | The Rust Ethereum L1/L2 execution client by LambdaClass - replaced a too-broad datadir non-empty startup check with an actual-DB probe, so unrelated files (e.g. an EthDocker JWT secret) no longer block a fresh node from booting (#6786). |
Personal projects
| Project | Description |
|---|---|
| kv-canary | A canary for silent KV-cache-compression failures - functional accuracy (code execution / tool-calls) vs perplexity under quantization & token eviction, scored by a Silent Degradation Score. |
| churn - StragglerPolicy | Deterministic discrete-event simulator of elastic-membership decentralized ML training, plus the straggler-aware membership policy behind the paper above. |
| CoinSwap (CosmWasm + Terraswap) | DEX swap contract for LUNA/UST/CW20 tokens, with a gas-fee analysis tool for the Terra blockchain. |
| Gas-Fee Benchmark (cw-storage-plus / Terraswap) | Benchmarking contract measuring gas costs of storage patterns on Terra/CosmWasm. |
| friendly-neighbourhood-6502 | Bare-metal systems - cycle-accurate 6502 CPU emulator down to bus/processor pins, addressing modes, and internal functions, with an OpenGL / Pixel Game Engine graphics frontend. |
| Solana Payment System | Rust payment-settlement program deployed on Solana. |
| Stader APR Dashboard | React dashboard surfacing staking APR and validator analytics. |
| Veri5 | Real-time identity and account verification API for cross-border payments. |
Languages
Blockchain & Web3
AI / ML Systems
Backend & Infrastructure
Achieved Codeforces Expert during university (pre-2022, before AI coding assistants) - a credential earned through unassisted algorithmic problem-solving under contest conditions.
- Codeforces - Expert · pjdurden
- CodeChef - peak rating 1890 · pjdurden
- LeetCode - peak rating 1679 · Pjdope
- Code-A-Thon - Rank 5 (College Rank 1)
- Cleared the Facebook Hacker Cup Qualification Round (2020); Google Kick Start Round B (2021).
- Mentored 300+ students in algorithms and software engineering through GirlScript.