The US Department of Energy (DOE) released the June 2026 update to 45ZCF-GREET, the lifecycle emissions model governing carbon intensity scores for the §45Z clean fuel production tax credit. The update reflects amendments to §45Z under the One Big Beautiful Bill (OBBB) and delivers targeted improvements across modeling inputs.
The update is primarily beneficial for crop-based liquid fuel producers. Negative-carbon-intensity (CI) biogas producers must await further updates.
For fuel produced after December 31, 2025, induced land use change (ILUC) emissions are excluded from lifecycle CI calculations. For crop-based pathways, ILUC had been one of the largest single CI components — soy-based renewable diesel carried roughly 13–14 gCO2e/MJ in ILUC alone; canola-based pathways carried more than 16 gCO2e/MJ.
Removing those values improves credit eligibility across the board and, for marginal pathways, can mean the difference between qualifying and not under the 47.4 gCO2e/MJ §45Z threshold.
The OBBB eliminated negative CI values for all non-manure renewable natural gas (RNG) pathways starting in 2026. Landfill gas and wastewater sludge producers can no longer claim below-zero CI scores. Animal manure–derived RNG is explicitly exempted, preserving the outsized credit economics.
The update left one item open: the generic "animal manures" pathway is retired for post-2025 production; species-specific pathways are now required. The DOE flagged that update for a future model release, delaying certainty for RNG producers in new negative CI scores.
Other updates in the June 2026 release
Additionally, the 45ZCF-GREET changelog reflects several technical improvements:
The model also generates separate CI outputs for fuel produced in 2025 versus fuel produced after December 31, 2025, eliminating the ambiguity that had complicated year-end planning for producers straddling both periods.
The GREET update addresses the emissions-modeling side of §45Z. The other half of the picture — feedstock-level CI scoring for crops grown using conservation practices — remains with the US Department of Agriculture (USDA). Agriculture Secretary Brooke Rollins told the House Agriculture Committee the USDA feedstock guidance is coming "this summer" and that it's "imminent."
That rule, when finalized, will determine whether corn, soy, and sorghum producers using practices such as no-till and cover crops can unlock premium CI values — and, by extension, higher tax credit prices — for their feedstocks.
For crop-based producers, the ILUC exclusion is already in effect. The USDA rule is the next unlock.
Questions about how the updated model affects your project's CI score or credit value? Contact the Crux team.
Understand the changes to §45Z tax credits in the US Department of the Treasury’s February 2026 proposed guidance.
Dive deeper into what final 2026–2027 Renewable Fuel Standard volumes mean for RNG, renewable diesel, sustainable aviation fuel, and ethanol producers.
Explore the role of §45Z tax credits in the larger transferable tax credit market in The State of Clean Energy Finance: 2025 Market Intelligence Report.
