Simon Willison adds four-player battles to his browser game with Claude Opus 5.5

What you could do with it

• A strategy game fan could invite up to three friends to play a four-player battle on the new Compass Rose map by sharing invite links or QR codes, with AI commanders taking any vacant seats ².
• A player could watch a recorded four-way AI match using the provided replay link to see the Goliath Armada mutator in action ¹.
• A developer could study how the model added the map and multiplayer code as an example of using AI to improve open-source software ¹.

From the announcement: A top-down view of a snowy browser-based strategy game map with game pieces and UI elements

Picture: simonwillison.net

A new map for four-way fights

Willison wrote in a blog post on October 24, 2026 that he wanted to expand the game beyond two-player matches ¹. He gave the request to Claude Opus 5.5, and the model produced a new map called Compass Rose along with the network code needed to support four simultaneous players .

The map is a 72-by-72 arctic grid with each team starting in one corner — blue in the bottom left, green in the top left, red in the top right and purple in the bottom right ². The map is painted once in blue's quarter and then rotated onto the other three sides, so every corner is identical . Frozen streams split the map like a pinwheel, each with a bridge and a ford, meaning every side has a neighbour across a stream on each flank and the far corner across the open centre . Five Uplinks are placed on the map — one in the centre and one near each bridge — and supply drops land four crates at a time .

How four-player mode works

A side is eliminated when its headquarters and every Goliath mech unit are destroyed, or when it resigns ². All remaining units and buildings destroy themselves, the Uplinks turn neutral, and the player who has been eliminated can watch the rest of the game with the fog of war removed . AI commanders pick a rival to focus on and attack whoever raids their base . Robot Love is banned on this map because it needs exactly two sides, and there is no Last Stand mode either . Two-player matches behave identically to how they did previously, meaning saved records and replays made in earlier versions remain compatible .

To play online, users pick Compass Rose and tap "Battle friends online" ². The lobby gives an invite link and QR code for each seat, and any empty seat goes to an AI commander . The game runs over the same relay used for online duels without changes to the relay itself . If a friend drops out, an AI stand-in plays their side until they return, and someone who reloads can rejoin from their invite link . The pause menu does not stop the battle since other players are still active, and the host must keep their page open and in front .

Other changes

Player @elialbert contributed a Shift+drag feature that lets you add multiple units to your selection at once ². New robot colours purple and green join the existing blue and red designs, with updated portraits and minimap colours ¹. The report now shows finishing order, a four-line chart and four stat columns . A replay link can be used to watch a four-way AI match that has the Goliath Armada mutator enabled, with each side beginning the game equipped with four large Goliath mech units .

The update is free and available to play in a browser ².

Key facts

• Version 14 of battledrones adds a four-player map called Compass Rose
• Claude Opus 5.5 created the new map and updated the multiplayer network code
• Up to four human players can battle online via invite links or QR codes
• The map is a 72x72 arctic grid with four identical corners and five Uplinks
• Shift+drag to add units to selection was contributed by @elialbert

Sources

1. Release: battledrones v14: Compass Rose, a four player map
2. Release v14: Compass Rose, a four player map · simonw/battledrones