2027 assurance timeline and planning guide
| Date | What happens | Source |
|---|---|---|
| Nov 18, 2025 | Ninth Circuit enjoins enforcement of SB 261 pending appeal; injunction denied for SB 253. | Court order · CARB advisory |
| Feb 26, 2026 | CARB approves the Initial Regulation. | CARB |
| Oct 12, 2026 | Initial Regulation approved by OAL and effective (17 CCR §§ 96070–96077). | CARB notice |
| Nov 10, 2026 | First SB 253 report due: Scope 1 and 2. CARB will accept it with or without assurance (first-year enforcement discretion). | CARB guidance |
| 2027 | Scope 3 disclosures begin. Assurance requirements, standards and deadlines for 2027+ are being set in a separate CARB rulemaking. | CARB · guidance |
Statutory schedule: SB 253 (Health & Safety Code § 38532) calls for limited assurance on Scope 1 and 2 at first and reasonable assurance later. The exact years that will apply in practice depend on CARB's pending rulemaking, so check CARB before relying on any date after 2026.
Planning steps
- Now to Nov 10, 2026: file your first report; capture lessons on data gaps.
- Q4 2026: run a readiness review; shortlist and contact assurers early.
- When CARB finalizes 2027 rules: confirm the accepted assurance standards and level, and sign the engagement.
- 2027: provide evidence, controls and methodology to your assurer; begin Scope 3 reporting.
Commonly used assurance standards
Providers commonly work under ISO 14064-3, AICPA attestation standards (e.g., AT-C 205/210), ISAE 3000/3410, ISSA 5000 and AA1000AS. CARB has not yet finalized which it will accept for 2027 onward.