The Australian Bureau of Statistics released some analysis of data collected in 2022 for their Survey of Disability Ageing and Carers (SDAC) - see https://www.abs.gov.au/statistics/health/disability/disability-ageing-and-carers-australia-summary-findings/2022 

There is a brief section on autistic Australians. It says simply: 

Autism and disability

A4 considers the 1.1% autistic Australians is not a helpful figure: we warn that it does not reflect the diagnosis rate in any part of the population. Diagnosis rates vary enormously with age, as we have previously indicated.

A4 understand that the ABS will provide a more substantial analysis of the data that it obtained about Autistic Australians in Oct 2024. 

A4 is puzzled that 8.6% (100%-91.4%) of Autistic Australians are not people with disability: the DSM-5 and DSM-5-TR diagnosis criteria for autism spectrum disorder (ASD) requires that a person "need support" in both Part A and Part B of those diagnosis criteria to meet the diagnostic requirement. It is unclear how a person needing support in those two areas does not have a disability: though this may reflect people with a diagnosis self-reporting that they don't need support. 

These results are significant. They show

• estimated growth in the autism diagnosis rate at around 9% per year from 2018 to 2022 - which is quite alarming. It is a higher rate than the growth limit on the NDIS. Previously, the increase was around 7% per year. The reported severity increased slightly while most people expect that the increase in diagnoses is from more milder cases being diagnosed. 
• 63% of autistic Australians are NDIS participants - 10% fewer than the estimated number of autistic Australians with severe or profound disability.
• 10% fewer autistic NDIS participants than the the number of autistic Australians with severe or profound disability - not all severely autistic Australians are on the NDIS (and there are very few autistic Australians (who have been diagnosed) who are aged over 65 years so not eligible for the NDIS).
• higher growth than the 8% p.a. rate that NDIS is meant to grow at. This means any CPI increases above -1% results in funding for individual autistic NDIS participants going backwards.
• Overall, autism presentation got slightly more severe from 2018 to 2022. 

Note that the data collection was one year later than the usual 3 year cycle. And the ABS took a year longer than usual to publish the results. A4 is disappointed that the ABS gave disability data a lower priority in their work schedule.