Hacktoberfest Hack Day Barcelona

Hacktoberfest Hack Day Barcelona

On October 24, we’re getting together at Plata’s Barcelona office for a one-day, in-person hackathon as part of Hacktoberfest 2026, a global technology festival organized by Major League Hacking (MLH) and DEV.

This year’s theme is open-source AI and open-weight models. You’ll have 5 hours to turn an idea into a working prototype. Using AI tools while you build isn’t just allowed, it’s encouraged.

CHALLENGES

Your project needs to fit at least one challenge, and you can compete in several at once. Full details are in the Prize Categories section.

1. Best Open-Source AI Project — the festival’s main challenge
   Build a project where open-source or open-weight AI is an important part of how it works. It could be an agent skill, a product built on an open-weight LLM or SLM, or your own or an improved open-source model harness. The project must be published in a public GitHub repository under an open-source license.

2. Best Use of Gemma 4 — by Google DeepMind
   Gemma 4 is a lightweight, multimodal open-weight model you can access through the Gemini API. Use it to build an assistant that understands both text and images, a focused AI tool for learning, creativity, or productivity, or simply to move fast from idea to prototype. Getting-started resources are in the Links & Resources section.

3. A Judge That Learns from an Expert — Plata Bank Challenge
   Evaluating AI products is increasingly handed off to LLM-as-a-judge models. The problem: their idea of a good answer often doesn’t match that of a domain expert who knows the product, the rules of the field, and what users actually need. Today, the judge prompt is usually tuned by hand, a couple of cases at a time. Your challenge is to automate that process. You’ll get an expert-labeled dataset and the same metric script used for final scoring; solutions are judged on hidden-test quality, cost, and speed.

4. Best Use of ElevenLabs
   Give your AI a voice. Build a voice agent, a creative audio experience, or a practical tool powered by speech recognition or text-to-speech. ElevenLabs should be a meaningful part of the project, not decoration.

PRIZES

For all participants:
— 1 free month of ElevenLabs Creator (131k credits)
— 25% off a General Attendee ticket to Web Summit 2026 (valid for one week after the hackathon)

For every member of the winning teams in all challenges:
— access to the online stream of Matemarketing and recordings from previous years

Plus, by challenge:

1. Best Open-Source AI Project
   — passe to Web Summit 2026 in Lisbon (Nov 9–12)
   — 3 months of ElevenLabs Pro for each team member (600k credits/month)
   — YubiKey 5 NFC or 5C NFC from Yubico
   — MLH swag bag
   — DEV Badges
2. Best Use of Gemma 4
   — a YubiKey 5 NFC or 5C NFC from Yubico
   — Belt bag from MLH
3. A Judge That Learns from an Expert:
   — The winning team receives an exclusive consultation with Plata’s Head of AI Engineering, available online or in person, online career consultation with a Plata Talent Acquisition Specialist.
   — The prize-winning team receives an online consultation with Plata’s Head of AI Engineering
4. Best Use of ElevenLabs
   — 3 months of ElevenLabs Scale for each team member (1.8M credits/month)

PARTNERS

MLH & DEV, Plata, Google DeepMind, DigitalOcean, ElevenLabs, Web Summit, Yubico, Matemarketing.

HOW IT WORKS

1. Team up — up to 3 people. Come with your own team, find teammates in advance in our Telegram chat, or team up on the day. Solo is fine too.
2. Pick an idea — no need to bring a ready-made project: per the official Hacktoberfest rules, work on your submission has to start at the event.
3. Build — 5 hours to design, build, and polish a working prototype.
4. Demo & judging — show what you built, get feedback from the judges, and the best projects take home prizes.

WHO IS THIS FOR?

AI and ML engineers, developers, and anyone who can and wants to build products on AI models. If your notes are full of ideas you never get around to, these are your 5 hours.

📍 Plata office, Edifici Colom, Av. de les Drassanes, 6, Floor 15, Barcelona
📅 Saturday, October 24, 2026
⏱ 11:00–18:00, check-in from 10:30
💬 Telegram chat: t.me/hacktoberfest_bcn