Postmortem of a Hindi-English voice agent for fintech: number readback and real concurrency were the real problems

admrys · reddit · 2026-08-25

The author built a Hindi-English (Hinglish) voice agent for an Indian fintech handling payment reminders, KYC follow-ups and account queries, and shares a candid postmortem of six months of work.

The assumed hard part—LLM understanding Hinglish—wasn't; making the agent speak correctly was:

Number readback: amounts, dates and reference numbers must be read digit by digit; early on full-English number chunks inside Hindi sentences felt scammy—fatal for trust in fintech.
Code-switch stutter: many TTS engines pause or shift accent at the Hindi↔English boundary; people hang up.
Latency under load: single-call demos looked fine, but at real outbound-call concurrency one provider spiked past 800ms. Measure at YOUR real concurrency—the demo number is a lie.
Compliance: RBI-adjacent scrutiny, data residency and SOC 2 disqualified several otherwise-good options.

The fix: a TTS treating Indian code-mixing and number normalization as first-class, plus testing through the actual telephony pipe at real concurrency. Once readback was clean, pilot trust and completion rates jumped. Meta-lesson: stop evaluating on "which voice sounds nicest" and start evaluating on correctly saying an amount, a date and a reference number in a Hinglish sentence, over a phone line, at scale.

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Postmortem of a Hindi-English voice agent for fintech: number readback and real concurrency were the real problems

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