JobyBots defaults to Gemini Flash but supports Groq (Llama 3.3) as a fallback and we've been A/B testing GPT-4o and Claude 3.5 Sonnet on the side. After 1,000 cover letters across the three frontier models, here's what we found.

Test setup

Same 1,000 job descriptions (UAE / Saudi / India / UK PM roles)
Same résumé context (7 years, data products, retail)
Same prompt template: 4-6 sentences, JD-aware, sign-off 'Best regards'
Blinded human review by 3 ex-recruiters scoring each on (a) personalisation, (b) tone, (c) ATS-friendliness

Headline results

Gemini Flash: avg score 7.4/10, cost $0.00002 per email, latency 800ms
GPT-4o mini: avg score 8.1/10, cost $0.0006 per email, latency 1,200ms
Claude 3.5 Sonnet: avg score 8.0/10, cost $0.003 per email, latency 1,500ms

At 200 emails a day, the lifetime cost difference at JobyBots' lifetime price (₹2,999) becomes meaningful: Gemini Flash costs you about ₹0.06/day; Claude costs ₹0.18/day. Both are negligible compared to LinkedIn Premium (₹2,400/month), but the engineering simplicity of Gemini's free tier (1,500 calls/day) won.

What each model does best

Gemini Flash — the volume engine

Gemini's strength is consistency at scale. The 4-6 sentence structure holds 99% of the time. The tone is professional-warm by default. The free tier (1,500 calls/day) covers two days of JobyBots at full 200-cap throughput, which means most users will never pay a cent.

GPT-4o mini — the creativity engine

GPT-4o produces the most natural opening lines and the most varied sign-offs. If you're applying to creative / consumer roles, this is the model that gets remembered. The cost — 30× higher than Gemini — is real but not crippling.

Claude 3.5 Sonnet — the accuracy engine

Claude was best at quoting the JD verbatim without paraphrasing it incorrectly. For senior roles where every word of the JD is calibrated, Claude's literal fidelity is a meaningful edge. Worth the 150× cost premium for late-stage applications.

Recommendation

Use Gemini Flash by default. Switch to GPT-4o on roles where you want to stand out emotionally. Switch to Claude on top-10 dream roles where every JD detail matters. JobyBots lets you swap the model via a single .env variable.