Arun Rajkumar

I've spent UK FinTech Week reading dev threads on open banking. Same misconceptions every time. PSD2 is "OAuth for banks." Payment Initiation is "just a bank transfer." Open banking is "Stripe but cheaper." None of that is right. Quick thread on what we got wrong (and learned). 🧵

Friday afternoon. Half the eng teams I know are running sprint retros right now. Mine isn't. We stopped doing sprints months ago. Building what comes next. More soon. #BuildInPublic #AI #StartupLife

@JakeATech cloudflare pages if it is static , you can get it for free

Where do you like to host your website for your work?

@Jhoncls4 Will do thank you

@mickyarun Hi! Would you like to list your project on a Product Hunt alternative for free? They’re looking for unique projects, and yours would be a great fit.

What are you working on this week?

@CiprianiRanieri Signed up

@mickyarun lets go Arun!! ps are you on builders map? builders-map.com

Founders only. Drop one number you're proud of. Followers. Users. MRR. Whatever. I'll go first. 1,150+ builders. ↓

@dgwbirch Tough discussion, also tough to balance cost vs adaptation. Let’s see what’s turning in over the years.

When it comes to open finance, banks have a point when they want a level playing field (with big tech). #Banking #OpenFinance #BigTech #OpenBanking #JPMorgan

@FriMikAnik @GoogleStartups 🤣

@GoogleStartups Starting a project on Google Cloud and all the setting up of roles

What’s the most manual part of your dev cycle?

@AravSrinivas Subagents inside an agent is where the actual product lives — single-model demos undersell this. What broke first when you scaled the orchestration?

A Google Earth + Flight Simulator, fully cooked by Perplexity Computer with Codex/CC as subagents inside it. GTA vibes.

@sytaylor Onchain BaaS for agents is the bit — agents will hold balances long before humans trust them with cards. What stops a regulated bank from launching the same surface, just slower?

🚨 JUST IN: Former PayPal CEO David Marcus just unveiled a stablecoin banking product for businesses and AI agents. Stablecoin balances. Yield. Payments. Cards. All chain-native, all behind an API. This is Banking-as-a-Service but onchain. --- Banking-as-a-Service is getting rebuilt on stablecoin rails. The old stack - Middleware (e.g. Unit / Synctera) - Galileo - FBO accounts at a sponsor bank There's now a chain-native version. - Squads Grid does it on Solana. - Bridge built it for fintechs, payroll and non banks - BVNK ships it embedded. Lightspark now joins them, with distribution into 65 countries and a Bitcoin L2 underneath. --- I keep thinking about how the "account" itself is being unbundled. What used to be a sub-ledger entry at a partner bank becomes a programmable smart account that holds dollars, settles 24/7, keeps its own yield, issues cards, and accepts agent-scoped permissions. The bank charter turns into a feature you plug in for accessing other rails. --- The agent piece is marketing, but its also more than that. Lightspark is already inside Google's AP2 protocol. As agents want to become platforms in their own right, re-sell financial services to their customers, they'd want a BaaS like thing. Why not go for something that uses stablecoins? --- Marcus has THE most fascinating back story - Former CEO of PayPal, has moved money traditionally - Behind Libra at Meta a global bank account and "stablecoin" that regulators pushed back on. Now this is a global stablecoin bank account distributed through an API, post-GENIUS Act, sold to businesses and machines. Sometimes timing is everthing. Does this compliment or commoditize BaaS over time? I expect the answer becomes obvious within 18 months.

@InnFin @JanineJoyHirt @neilshahuk @LSEGplc PISCES is the most underwatched UK structural reform of 2026 — pre-IPO liquidity is half the listing problem. Will it actually shift founder behaviour, or just ease the late-stage cap table?

@sytaylor @mercury The teams that ship CLIs first usually ship better APIs second — the constraint forces clean grammar. Who's done it best so far in payments?

Oooo @mercury just launched their CLI The day after they got their conditional OCC Charter Having a CLI is becoming tablestakes for finance companies github.com/MercuryTechnol…

@AlexH_Johnson CLI-first is also where agent-readability lives. Your stack is already agent-ready or it isn't — the bot just exposes the gap. What's the cleanest CLI you've seen out of fintech?

If you’re still talking about agentic commerce and not command line commerce you’re NGMI.

@harshilmathur That phrase is a tell. The last 6 months changed what one engineer can ship in a day, not the model. What's the call you wish you'd made 6 months earlier?

If a leader starts with “AI isn’t new to us, we’ve been doing it for 4 years..." There’s a good chance they’ve missed what actually changed in last 6 months.

Confession: most monitoring stacks I've inherited at startups were over-engineered for the stage of the company. Tried Beszel this week as a counter-experiment. 23 MB hub. 6 MB per agent. SSH-based pull. Docker container stats automatic. Zero YAML. Zero PromQL. It gets you about 80% of what you actually open a dashboard to look at — in an afternoon. Not built for 1,000-server fleets. Perfect for the staging box, the side project, the small team that just wants to know if a container died. The AI tooling cycle has been loud for weeks. Nice reminder that not every productivity win needs a model behind it. github.com/henrygd/beszel #OpenSource #DevOps #SelfHosted

A consultant told me last week she finishes the work in two days. Then spends two hours every Friday building invoices. PDF templates. Manual customer entry. Email it. Hope it doesn't land in spam. Wait three weeks. Chase. Repeat. We rebuilt invoices at @PayWithAtoa. Branded. Auto-filled from the last customer. Partial payments allowed. Paid straight from the customer's bank app. Half the cost of cards. FCA-authorised. Money in the account the same day. Stop building invoices. Send them. paywithatoa.co.uk #OpenBanking #UKFintech #Payments

Anthropic just published a postmortem. Three back-to-back regressions in Claude Code in six weeks. Reasoning got dumbed down. A cache bug made it forgetful. A system prompt change tanked coding quality. The line every "fire your developers, AI does it now" founder should print and frame: "This change made it past multiple human and automated code reviews, as well as unit tests, end-to-end tests, automated verification, and dogfooding." Six layers of automated checking. Caught by humans reading feedback. Their own older model didn't find the bug. The newer one did — only after an engineer fed it the right repo context. I lead engineering at a payments platform. We use AI everywhere — code review, migration, scaffolding, evals. It's a force multiplier. Every guardrail it runs inside — the lints, the eval suites, the alert thresholds, the rollback plan — was designed by an engineer who understood the failure modes. AI is a force multiplier on a competent team. It is not a substitute for one. Tools don't ship software. Engineers do. anthropic.com/engineering/ap… #AICoding @claudeai #Engineering #BuildInPublic

If you’re a vibe coder, let’s connect

@audiencon dev.to/mickyarun/i-as… did a experiment this weekend

Which model are you using as your daily driver right now? > Codex > Claude > GPT-5.5 > Other

@claudeai @OpenAI @GeminiApp @sama @bcherny

Here's what the single-shot benchmark missed: Codex won my engineering eval. Claude won my heart. Two more prompts + browser automation, and the site went live at brca.in — running Claude's design. Best instincts ≠ best collaborator. Different questions. 🔗 brca.in for more detail post dev.to/mickyarun/i-as…

My son's cricket coach asked me for a website. Same prompt to 3 coding agents: Codex GPT-5.5 Claude Opus 4.7 Gemini 3.1 Pro Five total runs at different effort levels. The winner wasn't decided by the model. It was decided by taste. 🧵