The final unresolved detail in the negotiations between the two leaders involves the amount of post-cloture time for nominees, the sources said, describing it as a minor hurdle.
The emerging accord is a major step away from the Merkley-Udall "talking filibuster" plan which would have required a filibustering minority to occupy the floor and speak ceaselessly until one side gives in. It's also more modest than Reid's middle-path proposal to McConnell, which would have shifted the burden from a majority seeking to advance legislation and nominations to a minority seeking to block them.
The major proponents of reform believe the Reid-McConnell deal under discussion would not make it easier to pass legislation, and believe the only meaningful upside is that it may speed up the confirmation of some judicial nominations.
The agreement would avoid the need for Reid to utilize the constitutional option and change Senate rules with 51 votes, a move that Reid said Wednesday morning he had the votes for but which many Republicans and Levin warned against using.
The negotiations may yet fall apart. But save for a last-minute collapse, the reforms would entail a two-year change to the filibuster that can be passed with 60 votes under a "standing order." If finalized tonight, the deal could be announced as soon as Thursday morning.