What the HydroCouple ecosystem is now — 45 repositories, interface spec 2.0.0-alpha.1, Open-Source SWMM 6.0.0-alpha.3, a Qt6 GUI, an MCP server and a 1,396-model benchmark platform — set against EPA SWMM 5.2.4. Updated 31 Aug 2026 from the live GitHub org and hydrocouple.org source.
Start hereThe April 2026 version of this app described a 36-repo org whose activity sat in a 2019 thread-safe SWMM fork. Four months later the org has a different centre of gravity. This tab is the delta; the other tabs are the detail.
What changed since April 2026
THEN → NOW
Repositioning. hydrocouple.org now leads with “Digital public water infrastructure, built in the open and ready for AI.” HydroCouple describes itself as the enabling architecture — open interface definitions, data standards, computational engines — and names Open-Source SWMM 6.0 (SWMM2D) as its flagship engine. The framing has moved from “a coupling framework that wraps SWMM” to “a SWMM initiative with a coupling standard under it.”
What this means for a SWMM5 modeller. The engine you would couple today is not the 2019 SWMMComponent wrapper around a thread-safe C fork. It is openswmm.engine: a C++20 rewrite with a reentrant handle API, a PyPI package, a Qt6 GUI, an MCP server for agents and Gymnasium environments for control. The EPA C tree is still there — preserved in src/legacy as a separate build target for side-by-side comparison.
The openswmm.* and openepanet.* family (none of it existed in April)
ArchitectureClick any block to expand it. Left is the EPA engine as it ships; right is the HydroCouple stack as of August 2026. Numbers marked measured came from reading or running the code, not from a README.
EPA SWMM 5.2.4 — Monolithic
HydroCouple / OpenSWMM 6 — Component-based
ComparisonThe April table had 16 rows. This one has 24, and every row whose right-hand cell moved since April carries a changed mark. The HydroCouple column names OpenSWMM 6.0.0-alpha.3 unless stated.
Feature-by-feature
Dimension
EPA SWMM 5.2.4
HydroCouple / OpenSWMM 6 (Aug 2026)
RepositoriesAll 45 repos under github.com/HydroCouple, read from the GitHub API on 31 Aug 2026 (name, last push, language, stars, fork flag, licence, description). Filter by family, search, sort. Cards with a teal edge were pushed in 2026.
45 repositories ·
TimelineTen years of HydroCouple in one column, with 2026 at full resolution. Teal dots are HydroCouple events; orange are EPA/legacy anchors. Dates are commit, release or article dates as published.
Chronology
Coupling flowTwo ways to run SWMM inside a composition in 2026: the classic HydroCouple component path through the Composer, and the engine-native handle API that everything new (GUI, Python, MCP, Gymnasium, wasm) is built on.
How a composition runs
The handle API, as measured on v6.0.0-alpha.2
Every call takes the handle; SimulationContext holds per-engine state. Two live engines in one process is documented in openswmm_hotstart.h and was verified in the browser build — two handles at distinct non-zero addresses. This is the property the 2019 Project* refactor was reaching for, now native to the engine rather than bolted on.
FindingsThings the documentation, the changelog and the source do not all agree on, plus results measured while building the companion apps in July–August 2026. Each entry names where the evidence sits. A finding is not a criticism — most were caught by the project’s own tests or fixed within days.
Verified findings, Aug 2026
Your roadmapThe six April items, each with what happened to it, followed by what the August state opens up. Status colours: green done, grey superseded by the project, amber still open.
April 2026 items — status
August 2026 — new openings
How to use this explorer
Brief — read the delta since April 2026 first; the hero numbers and the then→now strip are the whole story in thirty seconds.
Architecture — click blocks to expand. Left EPA, right HydroCouple/OpenSWMM 6.
Comparison — 24 rows; filter to only the rows that changed. Export CSV.
Repositories — all 45, filterable by family, searchable, sortable. Export CSV.
Timeline — 2016 → 31 Aug 2026, with the seven engineering-note articles and three alpha releases.
Coupling and Findings — how a run works, and where docs and source disagree.
Roadmap — the April items with status, and what August opens up.
Dark is the default; the toggle in the header gives Light and Auto (follows your OS). ? reopens this; Take the tour walks the tabs; Record walkthrough captures a captioned WebM of the app.