HUD is an RL-environment platform: an open-source SDK for building and running environments, hosted infrastructure, and a marketplace where independent builders sell environments to labs. Sandworld builds the environments themselves — deterministic app twins with published verifier QA. The overlap is smaller than it looks: HUD is infrastructure and distribution, Sandworld is a builder, and for some teams the two are complementary rather than alternatives.
How do Sandworld and HUD compare at a glance?
| HUD | Sandworld | |
|---|---|---|
| What it is | Environment SDK, hosted infrastructure and a marketplace | A builder of deterministic app twins and expert data |
| Catalog | 13,764 environments built on the platform | Six app twins |
| Agent surfaces | SSH, MCP, CDP and VNC | Typed tools in Claude, OpenAI and MCP formats |
| Grading | Partial-credit graders; QA agents audit for reward hacking | Per-check state and process verifiers; five seeded QA probes per task |
| Formats | Imports and exports Harbor tasks | HTTP API (reset, step, submit), MCP, Harbor task export (beta), ATIF trajectories |
| Mobile | None found on its public pages | Mobile-style twins, browser-based today |
| Stage | $16M Series A; customers include UiPath and Sharpe | Early-stage; no customers yet |
What does HUD offer?
- An open-source SDK (v6) whose environments expose SSH, MCP, CDP (Chrome DevTools Protocol) and VNC, with partial-credit graders, Harbor task import and export, and QA agents that audit for reward hacking (HUD docs, SDK repository).
- A DataVendor marketplace where independent builders sell environments to labs, moving “millions of dollars… each month”, announced with its $16M Series A in June 2026 (HUD).
- Scale of use: 13,764 environments built, with named customers UiPath and Sharpe (HUD). Its cloud is reportedly priced at $0.10 per environment-hour (RL List).
Where is HUD stronger?
- Infrastructure. Hosted, parallel environments with shell, browser-protocol and remote-desktop surfaces — the right fit for pixel-level computer-use agents, which Sandworld’s tool-driven twins don’t test.
- Standards. Harbor import and export makes HUD environments portable across harnesses.
- Breadth and distribution. Thousands of environments and a marketplace that already reaches labs.
- Customers and funding, which Sandworld doesn’t have yet.
How is Sandworld different?
- We build environments rather than a platform. Each Sandworld twin models one app category in depth — stock levels, coupon eligibility, refund windows, send limits, scams — with tasks designed around those rules.
- Deterministic, rerunnable QA. Every task runs five seeded probes (reference, do-nothing, random, truncated and noisy) and publishes an A–C grade, plus a collateral-damage check on every episode.
- Mobile-style consumer twins. We didn’t find mobile environments on HUD’s public pages; Sandworld’s Quickbasket and Coinpurse are phone-app twins, though they run in the browser today rather than on Android or iOS.
- Expert data in the same twins. Demonstrations are recorded through the same tools agents use and checked by the task’s verifier.
Which should you choose?
- Choose HUD if you need infrastructure to build and run many environments, desktop or browser surfaces for computer-use agents, Harbor portability, or access to a marketplace of third-party environments.
- Consider Sandworld if you want deep, policy-heavy app twins with published verifier QA and expert demonstrations inside them — and you’re comfortable working with an early-stage team.
For the surface trade-offs, see computer-use and mobile agent environments.