We covered the SB 253 reporting deadline extension to November 10, 2026, in our last update. That extension was about Scope 1 and Scope 2. The CARB SB 253 workshop picks up where that story left off, and turns to the harder question: how Scope 3 reporting will actually work starting in 2027.
Nothing from the July session is finalized. But the concepts CARB is testing now are the same ones that will define your Scope 3 data architecture next year, so it’s worth tracking closely rather than waiting for the final rule.
Before getting into Scope 3, here’s the short version of what’s already settled, in case you’re catching up:
For the full breakdown of the deadline change, see our earlier post on the SB 253 reporting deadline extension. Everything below is new ground: what CARB is proposing for the reporting cycle that follows.
The July 21 session was CARB’s fourth public workshop on the California Corporate Greenhouse Gas Reporting Program, run virtually over Zoom. The agenda had two parts: an update on Scope 1 and Scope 2 mechanics for 2027 and beyond, including data assurance, and a closer look at Scope 3 reporting options for 2027.
Both build directly on the March 23, 2026 workshop, where CARB first laid out its Scope 3 thinking. The CARB SB 253 workshop in July functions as a status check on those same concepts rather than a break from them, since the agency is still in pre-rulemaking mode and has not committed to a final approach.
This is the part worth building your data roadmap around now. CARB has floated three regulatory frameworks for how Scope 3 reporting phases in starting 2027, and each one changes the order in which your categories or business units would need to be reporting-ready.
| Option | How it works | Who reports first | The trade-off |
|---|---|---|---|
| 1. Broad applicability | All reporting entities disclose all 15 Scope 3 categories in 2027, with flexibility to exclude categories shown to be de minimis | Everyone, simultaneously | Heaviest lift up front, but no ambiguity about your filing year |
| 2. Sectoral phase-in | Scope 3 reporting starts in 2027 only for the highest-emitting sectors (transportation and industrial first) | Companies in flagged sectors | Faster runway if you’re outside the priority sectors, less if you’re inside one |
| 3. Category phase-in | All entities report Scope 3 in 2027, starting with the categories companies most commonly already track | Everyone, but only on their best-tracked categories first | Eases the data-maturity curve, but still requires 2027 readiness |
CARB has not indicated which option it favors, and public comments on the March concepts closed April 13. Until a formal proposal lands, the safest move is mapping your Scope 3 categories against all three so you’re not caught flat-footed by whichever one CARB adopts.
For Scope 1 and 2 limited assurance, expected to phase in from 2027, CARB is leaning toward accepting existing standards rather than writing a new one from scratch.
| Standard | Governing body | Notes |
|---|---|---|
| AT-C Section 210 or 205 | AICPA | Common for U.S.-based assurance engagements |
| ISAE 3000 (Revised) / ISAE 3410 | IAASB | Accepted through December 2026 |
| ISSA 5000 | IAASB | Effective December 2026; adopted across the EU, UK, Australia, Japan, and more |
| ISO 14064-3:2019 | ISO | Requires provider qualification under ISO 14065/14066 |
ISSA 5000 is the one to flag internally. If your company already reports under CSRD or a similar international framework, aligning to ISSA 5000 likely means reusing an existing assurance relationship instead of building a separate one for California.
Here’s the timeline from our last post, extended with the July 21 workshop.
The Scope 1 and 2 extension bought you time. The Scope 3 groundwork shouldn’t wait for it.
Whichever option CARB adopts, all three require the same underlying capability: supplier-specific Scope 3 data your team can defend, not spend-based estimates. Sprih’s AI engine, SustainSense, pulls from over 400,000 sustainability reports across 150,000+ companies to build that data without sending suppliers another questionnaire. For a deeper look at the mechanics, see our guide to Scope 1, 2, and 3 reporting under SB 253 and our breakdown of the SB 253 assurance requirement.
