I’m looking to build and ship LLM end-to-end, production-grade backends.
Looking for a job
Daniel del Castillo
@danieldelcastillo
Senior ML engineer focused on low-latency LLM systems, Agentic AI Voice Pipeline, and MLOps.
SpainWhat I'm looking for
I’m a Senior Machine Learning Engineer building production-grade, cloud-native AI systems with a strong focus on reliability, performance, and deployment. I help translate research into working products, defining MLOps best practices and architecting scalable ML systems for efficient inference, fine-tuning, and retraining.
In my freelance work (remote), I’ve led end-to-end implementations across data preprocessing, model fine-tuning, and scalable deployment. Highlights include a real-time LLM commentary system for online gaming using context engineering, a grounded healthcare conversational agent that generates summaries and discharge notes with verifiable citations, and a claim-matching fact-checking system powered by a fine-tuned cross-encoder reranker.
I also build voice-first, adaptive experiences—developing multi-agent voice tutor systems with an STT → LLM → TTS pipeline and optimizing latency for natural spoken interactions. Across these projects, I’ve designed modular, dockerized and streaming architectures that integrate event ingestion, TTS, and scalable microservice deployment.
Previously, I strengthened my foundation in ML safety and evaluation by red-teaming LLMs (jailbreaking, prompt injection) and implementing guardrails against adversarial attacks. I’ve also supported software and data engineering in roles spanning MLOps (AWS/GCP/Azure, Kubeflow, MLflow, Airflow), large-scale pipelines (SQL, Spark, Dataflow), and even HPC and test engineering—so I approach problems end-to-end, from experimentation to production.
Experience
Work history, roles, and key accomplishments
FR
Current
Freelance Senior ML Engineer
Freelance
Jun 2024 - Present (2 years)
Led end-to-end ML implementations for real-time LLM voice and commentary systems, including Dockerized, streaming architectures and TTS integration. Built grounded conversational and fact-checking agents using hybrid retrieval (BM25/FAISS/Pinecone) plus reranking and citation-focused answer generation.
FR
Senior Machine Learning Engineer
Freelance
Oct 2023 - May 2024 (7 months)
Translated ML research into production by coordinating across ML, software engineering, and product teams. Defined and enforced MLOps best practices while architecting scalable ML systems for efficient fine-tuning, retraining, and low-latency LLM inference.
FR
Machine Learning Engineer
Freelance
Oct 2021 - Sep 2023 (1 year 11 months)
Performed LLM red-teaming (jailbreaking, prompt injection) and designed guardrails to protect SOTA LLMs from adversarial attacks. Built LLM benchmarking/evaluation tooling and deployed training, evaluation, and testing pipelines in production.
FR
Freelance Software Engineer
Freelance
May 2021 - May 2023 (2 years)
Developed an AI-based TTS Python module (The Nonlinear Library) to increase the reach of EA-related content. Supported multiple AI safety initiatives including tools for knowledge bases and organizing competitions to amplify top researchers' impact.
SA
Machine Learning Engineer
Soundtrack Your Brand AB
Jan 2019 - Dec 2020 (1 year 11 months)
Designed AI solutions using literature reviews, processing large datasets with SQL and distributed data tools. Deployed large-scale training and evaluation pipelines and collaborated with product teams on new app features.
PK
HPC Engineer
PDC Center for High Performance Computing at KTH
Nov 2018 - Sep 2019 (10 months)
Supported high-performance computing cluster usage by troubleshooting technical issues and testing supercomputer applications. Collaborated on research projects and contributed to software tool development.
IN
Test Engineer
Indra
Aug 2016 - May 2017 (9 months)
Developed scalable, flexible software architectures for RF test benches across hardware definition and validation of devices under test. Built and iterated on bench development workflows end-to-end to support reliable testing.
NI
Applications Engineer
National Instruments
Feb 2015 - Mar 2016 (1 year 1 month)
Provided software and hardware technical support for software-connected automated test and measurement systems. Assisted with integration and troubleshooting for test and measurement workflows.
Education
Degrees, certifications, and relevant coursework
KTH Royal Institute of Technology
Master of Science, Machine Learning
2017 - 2019
MSc in Machine Learning with specialization in sequential models, deep learning, NLP, and music information retrieval (MIR).
Universidad Politécnica de Madrid
Bachelor of Science, Industrial Technologies
2011 - 2017
BSc in Industrial Technologies with a track in Automation, Electronics, and Computer Science.
CT
Colegio Los Sauces Torrelodones
Baccalaureate of Science and Technology, Science and Technology
2009 - 2011
Grade: Ranked 1st; Graduated with Distinction
Baccalaureate of Science and Technology, graduating with distinction.
Tech stack
Software and tools used professionally
Availability
Looking for a job
Location
SpainAuthorized to work in
Salary expectations
75k-125k USD
Social media
Job categories
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