Source: C's trade Anthony to Pistons

The Boston Celtics are working to finalize a trade that will send center Joel Anthony to the Detroit Pistons for Will Bynum, according to a league source.

The Celtics appear to be making the move with roster flexibility in mind. The Celtics have 16 fully guaranteed contracts on their books and must trim that down to 15 before the start of the regular season. Swapping Anthony, who is set to make $3.8 million this season, for Bynum, who will earn $2.9 million, will save the team $900,000.

It's not clear if Bynum will stick with the Celtics. It could hinge on whether the team makes any additional moves before the season tips later this month.

Anthony, 32, had played sparingly, including this preseason, since being acquired from the Miami Heat in January.

If the Celtics ultimately elect to waive Bynum, the $900,000 savings from the trade would give them additional flexibility with the goal of staying under the tax line this season.

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Update (1:02 p.m.): The Celtics formally announced the Anthony-for-Bynum swap.

And here's ESPN Insider's Kevin Pelton grading the trade for Boston:

Boston Celtics: B

The players involved don't really matter from the Celtics' perspective. Both have expiring contracts, and neither would have made an impact on the court, so from Boston's standpoint this move was strictly financial. With 16 guaranteed contracts, they had no choice but to eat a salary, and waiving Bynum's $2.9 million contract saves them nearly $900,000 compared to Anthony's salary.

Besides the actual cash, the savings are important because the Celtics had been just more than a million dollars below the NBA's luxury-tax threshold. Now, Boston has a little additional flexibility to take on salary in a future trade without paying the tax for a likely lottery team.

The Pistons emerge with a C grade.

(Read full Insider grade)