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Both are selective-application expert networks overlapping in law, medicine, and finance work, but HFC is Scale AI's fellowship-style network with roles concentrated in the US, UK, and Canada, while Mercor Experts is open globally, spans a broader set of domains including coding and consulting/ops, and currently lists far more active roles.

HFC and Meridial share law, finance, and science/STEM work, but Meridial (an Invisible Technologies-powered contractor network) covers a wider domain spread including coding, linguistics, and safety, and lists a much larger volume of open roles than HFC's smaller, region-limited fellowship network.

HFC and Vetto Opportunities both hire selectively for medicine and finance domain work, but sit under different parent companies (Scale AI vs. Vetto) with different secondary focuses - HFC also covers law and science/STEM, while Vetto also covers consulting/ops - and both currently have a comparatively small number of open roles.

Mercor Experts and Meridial are two of the largest expert networks by open-role volume, overlapping in law, finance, and coding work, which makes the choice between Mercor's profile/role application model and Meridial's Invisible-powered contractor network one of the more common comparisons for workers weighing where to apply first.

Mercor Experts and Vetto Opportunities both hire for medicine, finance, and consulting/ops work, but Mercor currently lists a much larger volume of open roles across a broader domain set, while Vetto's opportunities are narrower and more limited in number at any given time.

Prolific offers two routes in, which is the detail that matters most here: an open research-participant marketplace you register for, and an expert network hiring for AI training and evaluation work - the latter is where the role listings on this page come from. Mercor Experts is expert-network-only, selectively vetted through a profile and a per-role application. Both operate globally and overlap in medicine, finance, coding, and consulting/ops work, so the real differentiators are pay transparency and volume: Mercor publishes structured rates directly on each listing and its top hourly figures run well above Prolific's, whereas Prolific's rates are inferred from listing text. Read Prolific's posting count carefully too - one real requisition fans out across many city and language variants, so it represents far fewer distinct openings than the raw number suggests.

Both operate globally and overlap in coding, finance, and linguistics work, but they package it differently. Prolific has two routes in - an open research-participant marketplace you register for, plus an expert network hiring for AI training and evaluation - and lists effectively all of it as remote. Meridial (an Invisible Technologies-powered contractor network) posts country-specific freelance AI trainer projects across the US, India, the Philippines, Canada, the UK, and Singapore, so most of its listings are tied to a particular region even though the network itself is worldwide. Both carry an hourly figure on nearly every listing, but Meridial's skew markedly lower - the majority of its roles fall under $20/hr - while Prolific's cluster in the higher bands. Prolific's raw posting count is also inflated by one requisition fanning out across many city and language variants.

Both are globally open and route workers into fully remote AI training and evaluation work overlapping in coding and linguistics, but they differ in how you get in and in how the pay figures should be read. Prolific has two routes - an open research-participant marketplace you register for, and an expert network hiring for AI training and evaluation work - while Mindrift (the brand Toloka migrated its contributor work to) is a single specialist freelance track covering reasoning, coding, and multilingual evaluation. The important caveat is on Mindrift's rates: every one of its listings quotes only an upper ceiling ("up to $X/hr") with no floor, so its position in the higher pay bands reflects a best case rather than a typical rate, and the figure you are actually offered on a given project can be well below it.