The central caveat, up front: the Colorado model is a proposal — not yet on the ballot, let alone enacted or operating. Every other body compared here is real, running, and has a track record. A fair comparison has to keep those two things — designed power vs. demonstrated power — separate throughout.

The core question: what happens when the legislature says no?

This is the single factor that determines whether a citizen assembly has real power or just a strong suggestion. Across the world's leading examples, there are three tiers:

BodyStatusPopulationBudget in scopeIf the legislature/government rejects it…
Colorado proposal Proposed, not enacted ~6.0 million $46.8B state budget (FY26-27); ~5% of the legislative budget funds the assembly itself Automatic binding ballot — no legislative override possible, no signatures needed
Ostbelgien (Belgium) Operating since 2019 ~79,500 ~€405M regional budget (2020) Must respond & report — Parliament must keep the Citizens' Council informed in writing on implementation, but is not bound to adopt anything, and there is no referendum trigger
Paris Citizens' Assembly Operating since 2021 ~2.1 million City of Paris budget (~€10B) Must respond to every recommendation; can draft "Citizen Bills" the Council votes on directly (one passed 2023-24) — but the Council's vote is still the final word
Porto Alegre participatory budgeting Operating since 1989 ~1.5 million Directly, bindingly allocates 9-21% of the actual city budget Binding on that slice of spending by design — but this is spending-allocation power only, not general policymaking power
Ireland Citizens' Assembly (2016-18) One-time, concluded ~5 million N/A — advisory on a single constitutional question No binding mechanism — parliament chose to hold the 2018 abortion referendum after deliberating on the Assembly's report. It worked, but nothing structural required it to
France Citizens' Convention for Climate One-time, concluded 2021 ~68 million N/A — advisory on climate policy Promise broken — Macron pledged "sans filtre" transmission to referendum, then unilaterally exempted proposals he disliked. ~20% survived into law unmodified

Sources: Ostbelgien figures from the Deliberative Democracy Digest, Bürgerdialog.be, and BRF/CSP-DG budget reporting; Paris from DemocracyNext and the Sortition Foundation; Porto Alegre from Boston Review and the World Bank participatory-budgeting case studies; Ireland from the Citizens' Assembly's own published record and Electoral Reform Society; France from Verfassungsblog and the Deliberative Democracy Digest. Colorado figures from the Colorado Sun and Colorado Newsline (FY26-27 budget) and Colorado state demography estimates.

On mechanism strength: yes, this is the "hardest" design yet

Every operating example above tops out at an obligation to seriously consider and respond — Ostbelgien and Paris both require the elected body to engage and answer, but neither requires it to act, and neither has any fallback if it doesn't. France shows exactly how that plays out when even a presidential promise of "no filter" turns out to be unenforceable: the moment the executive changed his mind, there was no mechanism to hold him to it. Ireland shows the pattern can still work — a citizens' assembly's report can lead to a real, binding referendum — but only when the political will lines up at each step; nothing in the law required it.

Colorado's design is different in kind, not just degree: rejection or inaction by the legislature doesn't end the process, it triggers the next one — an automatic, no-signature statewide ballot vote. On this axis specifically — what happens when elected officials say no — nothing in current practice matches it. That part of your claim holds up.

On scale: Colorado is enormous by comparison, but that's Colorado, not the mechanism

Colorado's population (~76×) and state budget (roughly 100×) dwarf Ostbelgien's — the only directly comparable "permanent institutionalized deliberation" precedent. But that's almost entirely because Colorado is a large U.S. state and Ostbelgien is a small linguistic community of ~80,000 people, not because the Colorado design is more powerful per person or per dollar. It's worth keeping scale and mechanism as two separate claims: Colorado's mechanism is more binding; Colorado's reach is larger because Colorado itself is larger. Both are true and both matter, but they're different arguments.

On scope: the federalism ceiling applies on both sides

Colorado cannot touch immigration, foreign policy, currency, or other federally-reserved matters — those sit with the U.S. federal government under the Constitution. Ostbelgien faces the same structural ceiling one level down: as a "community" within Belgium's federal system, it holds real legislative power over education, culture, health and social policy, environment, and some spatial planning — but not federal matters like defense or foreign affairs, which sit with Belgium's national government. In both cases the assembly's power is real but bounded by a higher layer of government; Colorado's bounded layer (U.S. federalism) happens to leave state governments more fiscally and substantively powerful in absolute terms than Belgium's leaves its language communities, but the shape of the limitation is structurally similar.

The one place a different kind of "muscular" already exists today

Porto Alegre's participatory budgeting is worth naming separately because it's the one example on this list with real, tested, binding power operating right now — not a promise, not a proposal, an actual mechanism that has allocated a fifth of a real city's budget for over three decades. It's a narrower domain (spending allocation, not general policymaking), but on its own terms it's arguably the most proven "muscular" citizen body in the world today.

Verdict: As designed, the Colorado proposal's automatic-ballot-bypass mechanism would be the most legally binding response-to-rejection guarantee of any citizen assembly yet devised — more so than Ostbelgien, Paris, or the ad hoc Ireland and France examples, all of which stop at "the government must engage with this" rather than "the government's inaction has an automatic consequence." Calling it, once enacted, potentially the most muscular constitutionally-guaranteed citizen assembly mechanism in history is a defensible, fact-grounded claim on that specific axis.

But three qualifiers keep this honest: (1) it doesn't exist yet — every comparator here is a real, operating institution with a track record, and Colorado is not; (2) its sheer scale advantage over Ostbelgien is a function of Colorado's size, not the mechanism's design; and (3) on a different axis — real, tested, binding power in continuous operation today — Porto Alegre's participatory budgeting already has a thirty-plus-year track record that Colorado's proposal has yet to earn.