Twitter fired Zatko in January.
The company declined to comment about the reported settlement.
Twitter has disputed Zatko’s claims and says his complaint is inaccurate, inconsistent and lacks context.
The revelation of a settlement adds another twist to Twitter’s chaotic year.
Twitter and Musk are scheduled to go to trial on Oct. 17.
On Friday, Musk again tried to use the settlement to end his deal with Twitter.
Twitter didn’t immediately respond to a request for comment about the letter.
Zatko is scheduled to testify before the US Senate Judiciary Committee on Tuesday about Twitter’s security issues.
