The language of the 2023 MPFS final rule states that the policy for observation billing has not changed, in that the provider who orders the observation care will still be the only one who can bill the observation care codes (now coded as IP/OBS) and other providers (consultants) who see the patient during the observation stay will continue to bill the outpatient/office codes:
We are also not changing policies affecting billing, at this time, when multiple practitioners furnish E/M services to the same patient on the same day (such as the policy in Chapter 12 of the Medicare Claims Processing Manual (IOM 100-04), section 30.6.8.A, which specifies that while the practitioner who orders the observation care for a patient may bill for observation care, other practitioners providing additional evaluations for the patient bill their services as O/O E/M codes.) We are also not currently making any changes to current policy on the use of the AI modifier.
Here's a link to the complete final rule:
https://public-inspection.federalregister.gov/2022-23873.pdf. The language above can be found on page 528 of the pdf document, but the section on E/M coding and the new changes begins on page 498 and is worth reading in its entirety as it addresses many of the questions that have come up due to this year's CPT changes.