# Portal Agent – Astra reaches Portal endgame

> Source: <https://github.com/cozyblaze/portal-agent/tree/main>
> Published: 2026-09-07 17:47:31+00:00

This is the setup I used for my **GPT-6 Astra Portal run**, which reached the end credits on September 5, 2026 (San Francisco time, PDT / UTC−7).

**Portal pauses while the agent thinks.** The agent sees screenshots, player position, and camera angles, chooses its next inputs, then lets the game advance and checks the result.

``` php
flowchart LR
    A[Codex / GPT-6 Astra] -->|JavaScript plan| B[Local MCP server]
    B -->|TCP on 127.0.0.1:27182| C[Custom SourcePauseTool]
    C -->|Play N ticks, then pause| D[Portal]
    D -->|Screenshot + position + facing| C
    C --> B
    B --> A
```

The run used `gpt-6-astra` with `max` reasoning effort and took about **23 hours 43 minutes**, including capacity interruptions and waiting. I resumed it after capacity errors and switched to Fast mode. The agent handled gameplay throughout; after the initial goal, my only additional instruction was to leave the credits rolling.

- **[How it works](/cozyblaze/portal-agent/blob/main/docs/how-it-works.md)** — what the agent saw and controlled.
- **[Run it yourself](/cozyblaze/portal-agent/blob/main/docs/setup.md)** — the tested Windows setup.
- **[Read the session log](/cozyblaze/portal-agent/blob/main/evidence/README.md)** — the agent's messages, actions, and results.

The controller and SourcePauseTool changes here are the versions used during the run. Game files are not included; you'll need your own copy of Portal.

## Source files and technical reference

| Folder | Contents | 
|---|---|
| `controller/` | Game controller, [API reference](/cozyblaze/portal-agent/blob/main/controller/mcp/portal-documentation.md) , and tests | 
| `run/` | Agent instructions and configuration template | 
| `game-config/` | Game settings and the SPT loader file | 
| `spt/` | SourcePauseTool changes and [version details](/cozyblaze/portal-agent/blob/main/spt/UPSTREAM.json) | 
| `evidence/` | Sanitized session log and summary | 
| `tools/` | Setup and export helpers | 

Controller code uses [MIT](/cozyblaze/portal-agent/blob/main/controller/LICENSE); SourcePauseTool retains its [upstream license](/cozyblaze/portal-agent/blob/main/spt/LICENSE) and [credits](/cozyblaze/portal-agent/blob/main/spt/NOTICE). Portal belongs to Valve. Documentation and session evidence have no additional license grant.

Personal information and embedded screenshots were removed from the shared log. See [privacy notes](/cozyblaze/portal-agent/blob/main/docs/publication.md).