Melty Gym

Melty Gym is the product formally named on 13 November 2026 (UTC) by Melty, a Y Combinator Fall 2026 company, for turning games into environments for robotics and multi-agent training and evaluation. Founder David Miller (@davidmilr) posted at 19:11:56Z (03:11:56 on 14 November, Asia/Shanghai): “Train robots in any game at massive scale. Introducing Melty Gym!”, with a 33-second launch video. The same public write-up appeared on Launch YC as Melty Gym: Programmable games for RL and evals. The company site is https://www.melty.gg.

The Launch YC page summarizes Melty Gym as “Turn games into environments for robotics and multi-agent collaboration.” It says the team is building Melty Gym so researchers can drop their own models and robots into custom games, then adjust the mechanics, objectives and team dynamics to fit their needs. Games already require planning many steps ahead, mastering complex mechanics and coordinating a team; Melty says it builds on that to quickly create custom training tasks for spatial reasoning and multi-agent collaboration. The demo described on the page has humanoid robots gather and drive in GTA V, then work at server racks in a custom data center.

The same page also lists other Melty products: Melty Net (add 256-player multiplayer to games, mods, and mashups), Melty MCP (create custom games with a single prompt to a coding agent), Melty Chat (create and customize games by chatting with Melty), and the existing Melty Mashups (combine games you already own). The company homepage still mainly describes mashups and mods: it says Melty and its mashups are free, and that mashups run on games the user already owns. The new name recorded on this page is Melty Gym; do not treat those other product lines as first appearances in this announcement.

On availability, the Launch YC page says “We’re building Melty Gym,” that “We’re already building custom training tasks with teams,” and that people who need custom environments for RL or evals can reach [email protected]. Do not describe Melty Gym as a generally available self-serve product for all users, and do not describe Melty’s earlier Mashups product as Melty Gym.

Key points:

• Founder post: https://x.com/davidmilr/status/2121320174452121635 (2026-11-13T19:11:56Z / 03:11:56 on 14 November, Asia/Shanghai); Launch YC: https://www.ycombinator.com/launches/XT3-melty-gym-programmable-games-for-rl-and-evals ; site: https://www.melty.gg ;
• This is a concrete product name confirmed by the founder’s public post and the Launch YC page on 13 November 2026. The public materials describe custom training work with teams; do not describe it as generally self-serve or already open to everyone.

Why it matters

This is a new product formally named on 13 November 2026 by Melty’s founder post and Launch YC page, not an unnamed feature update to the company’s existing Mashups product. The founder post at 19:11:56Z (03:11:56 on 14 November, Asia/Shanghai) falls inside the earlier 04:32 scan window (00:32–04:32 Asia/Shanghai), but the 04:32 and 08:32 scans did not write it to the database; this 12:32 scan is a catch-up.

This page only restates the founder post, the Launch YC page, and the public homepage at melty.gg. Claims about using games as training environments, the demo setting, and current custom work with teams come from those sources. This page does not independently evaluate the product.

Limits

The public record does not give pricing, a self-serve availability timetable, a list of supported games or robots, or a standalone technical report or benchmark. Do not describe Melty Gym as a generally available self-serve product, and do not describe it as the same product as the earlier Melty Mashups.

1. Read the Launch YC page at https://www.ycombinator.com/launches/XT3-melty-gym-programmable-games-for-rl-and-evals , and cross-check the founder post at https://x.com/davidmilr/status/2121320174452121635 and the site at https://www.melty.gg ;
2. Per the official description, the public materials describe custom training work with teams; people who need environments for RL or evals can reach [email protected] — do not describe it as already open to all users as a self-serve product;
3. When citing the GTA V demo, spatial-reasoning and multi-agent training, or “drop their own models and robots into custom games,” attribute them to the 13 November 2026 Launch YC page or founder post, and recheck the upstream source;
4. Do not describe Melty Gym as Melty Mashups, and do not describe it as generally self-serve; this page only restates public materials — recheck the upstream sources before citing them externally.