The Department of Energy on June 12, 2026 released an updated version of the 45ZCF-GREET model, the carbon-intensity calculator that producers must use to determine their per-gallon 45Z Clean Fuel Production Credit value. The model is presented in two calculation tracks — one for fuels produced during the 2025 calendar year and a separate one for fuels produced after December 31, 2025 — reflecting the statutory changes introduced by the One Big Beautiful Bill Act (P.L. 119-21), signed July 4, 2025. Industry groups including Growth Energy and the Clean Fuels Alliance have welcomed the release as a long-awaited piece of regulatory certainty for current-tax-year production economics.
The substantive changes are narrower than the trade-press reaction suggests. The headline change is the formal removal of indirect land-use change penalties on US biofuels from the model’s carbon-intensity calculations, reflecting the statutory direction OBBBA gave to Section 45Z. The second is that the model now operationalises OBBBA’s statutory restriction of qualifying feedstocks to those originating in the United States, Mexico and Canada for fuels produced after December 31, 2025 — eligibility itself is a Code matter administered by Treasury, but the GREET calculation is now aligned to it. The third tranche is a set of technical refinements: species-specific RNG pathways replacing generic animal-manure pathways, a new carbon-capture-and-sequestration parameter, moisture content as a user input for corn stover Fischer-Tropsch SAF pathways, and new pretreatment options (diluted acid; deacetylation and mechanical refining) for corn stover fermentation.
This update to the 45Z CF-GREET model builds on the progress made by Congress and President Trump in the One Big Beautiful Bill Act (OBBBA) by reaffirming the removal of flawed indirect land-use change penalties on American biofuels and supporting the eligibility of undenatured fuel ethanol for American exports.
That framing, from Growth Energy CEO Emily Skor, identifies the headline lever. Kurt Kovarik, Vice President of Federal Affairs at Clean Fuels Alliance America, described the release as the moment biodiesel, renewable diesel and SAF producers gain certainty those changes can be claimed for the current tax year. The SAF-specific implication is that producers running HEFA, ATJ and PtL pathways now have a single sanctioned model to determine the carbon-intensity floor that drives their credit value, and the OBBBA feedstock restriction — as operationalised by the model and administered through the Code — tightens the working definition of what counts as a 45Z-qualifying barrel.
The piece that is not in this release is worth holding onto. Three pieces are required for full 45Z implementation: the DOE GREET model (now in place), the USDA farming-practices calculator (still in interagency review at last public update) and Treasury final guidance explaining how producers claim the credit. Treasury issued the proposed regulations under REG-121244-23 in February 2026 (published in the Federal Register on February 4), and a three-day telephonic hearing was held May 27-29. The final regulations have not yet issued. Producers can now run CI calculations under the sanctioned model, but the proposed regulations’ applicability-date rules mean today’s outputs are not fully locked until the final rule confirms the model-use terms.
The forward read is on cash-flow timing rather than producer economics. Most US SAF producers had been waiting on this model to size their first-half-2026 45Z accruals. The WSU 2030 US SAF supply forecast SAFpath covered last month assumed the 45Z framework would settle in a form that did not undermine the incentive stack. The remaining variables are Treasury’s final rule and the USDA practices calculator. Once both are in place, the first wave of accrued 45Z claims can be converted into actual returns and the financing picture for the next set of US SAF FIDs becomes materially clearer.
