All ns-3 releases are archived: the short links below provide quick access to the source code, releases notes, and documentation of every past release:

Release	Date
ns-3.43	October 2024
ns-3.42	May 2024
ns-3.41	February 2024
ns-3.40	September 2023
ns-3.39	July 2023
ns-3.38	March 2023
ns-3.37	November 2022
ns-3.36	April 2022
ns-3.35	October 2021
ns-3.34	July 2021
ns-3.33	January 2021
ns-3.32	October 2020
ns-3.31	June 2020
ns-3.30	August 2019
ns-3.29	September 2018
ns-3.28	March 2018
ns-3.27	October 2017
ns-3.26	October 2016
ns-3.25	March 2016
ns-3.24	September 2015
ns-3.23	May 2015
ns-3.22	February 2015
ns-3.21	September 2014
ns-3.20	June 2014
ns-3.19	December 2013
ns-3.18	August 2013
ns-3.17	May 2013
ns-3.16	December 2012
ns-3.15	August 2012
ns-3.14	June 2012
ns-3.13	December 2011
ns-3.12	August 2011
ns-3.11	May 2011
ns-3.10	January 2011
ns-3.9	August 2010
ns-3.8	May 2010
ns-3.7	January 2010
ns-3.6	October 2009
ns-3.5	July 2009
ns-3.4	April 2009
ns-3.3	December 2008
ns-3.2	September 2008
ns-3.1	July 2008

The full directory of releases is available here.