A planned 24-hour strike by Southern Railway workers next week in a dispute over ticket office closures has been suspended, but a guards walkout will still go ahead.
Members of the Rail, Maritime and Transport (RMT) union were due to take action on September 7 in protest at plans to close a number of ticket offices.
The union said "significant progress" was made in talks at the conciliation service Acas on Wednesday.
But the union confirmed that a 48-hour strike on September 7 and 8 in a separate dispute over the role of conductors will go ahead as planned, accusing the company of refusing to engage in talks without preconditions.
The RMT said new ticket office arrangements will now be trialled at eight locations, with no extension without union agreement.
The trials will prevent workers being left alone carrying cash, and there is a guarantee that no jobs will be lost and there will be no changes to terms and conditions. Staff volunteering for the trials will be paid an additional £1,000, said the union.
RMT general secretary Mick Cash said: "It is a testament to the solidarity and determination of our station staff members on Govia Thameslink that we have been able to achieve significant progress in the talks at Acas that have enabled us to suspend next week's action.
"The leverage from the vote for strike action has been pivotal in securing the package of measures that will protect jobs, safety and the services we deliver to the travelling public.
"The separate dispute on Southern over guards and safety remains unresolved and the strike action involving our members next week goes ahead as planned.
"The union will be focusing all of its efforts on supporting this safety-critical group of members as they continue to fight for safe, secure and accessible services for all."