Senior Applied ML Engineer — Model Router (Remote • Equity)

Cast AI; Spain; Remote; EUR 110,000 - 170,000; Full time

Benefits offered by this job

Competitive salary

Remote-first global environment

Equity options

Rapid feature delivery (1–4 weeks)

Learning budget & hackathons

Equipment budget

Job summary

Cast AI is building an applied ML role focused on real-time routing decisions for model selection and cost-efficient inference. You will own the routing model lifecycle, run production-parity evaluations, and transform fleet data into actionable training signals.

The role blends ML research rigor with practical engineering to ship reliable, fast routing across models. We offer remote-first, global collaboration across teams, equity options, and a fast-paced environment where feature projects

Qualifications

• 5+ years in applied ML or ML research with real-time decision models.
• Strong Python and SQL at scale to process millions of request-level records.
• Experience with model routing or LLM routing.
• Understanding of serving realities (TTFT, decode speed, batching, concurrency).
• Ability to instrument before optimizing, with error bars.
• A broad mandate and fast-paced delivery excite you.

Responsibilities

• Own the routing model end to end: features, objective, training, calibration, and release cadence.
• Build production-parity evaluation gates: benchmarks, router-vs-router comparisons, holdouts by task family, error bars on pass rates.
• Turn fleet data into training signals with proper failure categorization to avoid poisoned labels.
• Model the user-visible objective: task success × token cost × wall-clock speed under concurrency.
• Run the online loop: shadow, A/B, full rollout, drift monitoring, retrain.
• Push frontier with calibrated decisions and speed-aware routing.
• Collaborate with platform engineers on instrumentation and data pathways.

Skills

Applied ML experience

Python

SQL at scale

Model routing

Benchmarking

Online experimentation

Tools

Python

PyTorch

SQL (ClickHouse)

LLM APIs

RouterBench

GitLab CI

Job description

Cast AI is building an applied ML role focused on real-time routing decisions for model selection and cost-efficient inference. You will own the routing model lifecycle, run production-parity evaluations, and transform fleet data into actionable training signals.

The role blends ML research rigor with practical engineering to ship reliable, fast routing across models. We offer remote-first, global collaboration across teams, equity options, and a fast-paced environment where feature projects