2007 book "Firstborn", the third and last book of "A Time Odyssey" trilogy by Stephen Baxter and Arthur C. Clarke - an "orthoquel" to "2001: A Space Odyssey" - ends with a cliffhanger which obviously implies continuation:
Myra said, “My God.Charlie? ”
Bisesa stared. “Who is ‘we’?”
“We call ourselves the Lastborn. We are at war. We are losing.” She held out her hands. “Please. Come with me now.”
Bisesa and Myra, still hugging each other, reached out their free hands. Their fingertips touched Charlie’s.
A clash of cymbals.
However, sadly, Sir Arthur died in 2008, with no further books forthcoming.
Did Stephen Baxter or Arthur C. Clarke's estate ever comment on continuing "A Time Odyssey" after 2008?
Wikipedia has no info:
The 2008 Gollancz edition of the most recent book describes itself on the cover as the "Conclusion" of the series, but the plot is not concluded in the book. The immediate threat is averted but the enemy is not defeated, suggesting that further novels in the series were intended. With the death of Clarke, one of the two authors, it is not clear whether these will be written.