Scaling an LLM Email Assistant from 10K to 100K Users
How we helped Europe's first LLM-powered email assistant scale 10x while reducing infrastructure costs by 40-50%
Project Overview
Flowrite revolutionized professional email communication as Europe's first LLM-powered email assistant. Our team was brought in to architect and build the AI backend systems that would power their rapid growth from 10,000 to 100,000 users.
The engagement culminated in Flowrite's successful acquisition in 2024, with the robust technical foundation we built being a key factor in the deal.
The Challenge
The Challenge
In mid-2022, Flowrite was among a handful of companies globally shipping production LLM products. There was no established playbook for cost management, latency optimization, or observability.
- Rapid User Growth - Scaling from 10,000 to 100,000 users in record time
- Unpredictable Costs - LLM inference costs could spike 10x overnight with viral mentions
- Latency Requirements - Users expected instant email suggestions, but GPT-3 took 2-5 seconds
- Single Provider Risk - Dependency on OpenAI during frequent API outages
- No Standard Tools - No established tools for monitoring LLM output quality
Our Solution
Our Solution: Multi-Provider LLM Architecture
We built a resilient, cost-optimized AI backend that could handle 10x growth while actually reducing per-user costs.
Multi-LLM Provider Strategy
Integrated OpenAI and Cohere with an intelligent router that classified requests by complexity. Simple completions went to cheaper, faster models; nuanced emails used GPT-3.5/4.
Streaming Response Delivery
Implemented Server-Sent Events (SSE) to stream responses character-by-character, dramatically improving perceived latency.
Aggressive Prompt Caching
Built a semantic caching layer that recognized similar email contexts. Cache hit rates of 40%+ meant significant cost and latency savings.
AI-Specific Observability
Integrated monitoring tools for LLM quality tracking, detecting prompt injection, and measuring model drift over time.
Results & Impact
Results & Impact
- 10x User Growth - Scaled from 10,000 to 100,000 users seamlessly
- 40-50% Cost Reduction - Through intelligent routing and caching
- Sub-Second Perceived Latency - Via streaming responses
- 99.9% Uptime - Multi-provider fallback eliminated single points of failure
- Successful Acquisition - Technical foundation was key factor in 2024 acquisition
The robust AI infrastructure we built enabled Flowrite to focus on growth and user experience, ultimately leading to their successful exit.
Technologies Used
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